Building Cluster-Safe Once-Only Methods with Locks, Java and Postgres or DynamoDB

In distributed systems, ensuring that certain operations execute only once across multiple instances is a critical requirement. Whether you’re processing payments, sending notifications, or performing data migrations, you need guarantees that these operations don’t accidentally run multiple times. This article explores how to use PostgreSQL advisory locks through the lock-postgres utility to create cluster-safe once-only methods in Java.

See here for our OSS implementation of cluster locks using postgresql. We also have an implementation using DynamoDB here (same API).

The Challenge of Distributed Execution

Consider a common scenario: you have multiple instances of your application running in a cluster, and each instance processes scheduled tasks. Without proper coordination, you might end up with:

  • Duplicate payment processing
  • Multiple notification emails sent
  • Race conditions in data migrations
  • Resource contention issues

Traditional Java synchronization mechanisms like synchronized blocks or ReentrantLock only work within a single JVM. For cluster-wide coordination, you need a distributed locking mechanism.

Solution 1: Using PostgreSQL Advisory Locks

PostgreSQL provides advisory locks – lightweight, application-level locks that don’t interfere with table-level locks. These locks are perfect for coordinating application logic across multiple instances.

The lock-postgres utility leverages PostgreSQL’s advisory lock functions:

  • pg_try_advisory_xact_lock(key) – Non-blocking lock attempt
  • pg_advisory_xact_lock(key) – Blocking lock acquisition

These locks are automatically released when the database transaction commits or rolls back, making them ideal for transactional operations.

Solution 2: Using DynamoDB and the AWS AmazonDynamoDBLockClient

We also have a dynamo DB solution using the AWS AmazonDynamoDBLockClient as the implementation of the Lock API. This is an implementation of the same lock API in the examples in this article.

Setting Up the Dependencies

First, add the required dependencies to your project:

PostgreSQL implementation:

<dependency>   
  <groupId>com.limemojito.oss.standards.lock</groupId>  
  <artifactId>lock-postgres</artifactId>
  <version>15.3.2</version>
</dependency>

DynamoDB Implementation

<dependency>   
  <groupId>com.limemojito.oss.standards.lock</groupId>  
  <artifactId>lock-dynamodb</artifactId>
  <version>15.3.2</version>
</dependency>

Basic Usage Pattern

The PostgresLockService implements the LockService interface and provides two primary methods for lock acquisition:

@Service
@RequiredArgsConstructor
public class OnceOnlyService {   
     private final LockService lockService;   
     private final PaymentProcessor paymentProcessor;        
     @Transactional    public void processPaymentOnceOnly(String paymentId) {
        String lockName = "payment-processing-" + paymentId;
        // Try to acquire the lock - non-blocking
        Optional<DistributedLock> lock = lockService.tryAcquire(lockName);
        if (lock.isPresent()) {           
          try (DistributedLock distributedLock = lock.get()) {                
                // Only one instance will execute this block
                paymentProcessor.process(paymentId);
                log.info("Payment {} processed successfully", paymentId);
           }
        } else {
            log.info("Payment {} is already being processed by another instance", paymentId);
        }
    }
}

Blocking vs Non-Blocking Lock Acquisition

The lock service provides two approaches:

1. Non-Blocking (tryAcquire)

@Transactional
public void tryProcessOnceOnly(String taskId) {
    Optional<DistributedLock> lock = lockService.tryAcquire("task-" + taskId);
        if (lock.isPresent()) {
        try (DistributedLock distributedLock = lock.get()) {
            // Process the task
            performCriticalOperation(taskId);
        }
    } else {
        // Task is being processed elsewhere, skip or handle accordingly
        log.info("Task {} is already being processed", taskId);
    }
}

2. Blocking (acquire)

@Transactional
public void waitAndProcessOnceOnly(String taskId) {
    // This will wait until the lock becomes available
    try (DistributedLock lock = lockService.acquire("task-" + taskId)) {
        // Guaranteed to execute once the lock is acquired
        performCriticalOperation(taskId);
    }
    // Lock is automatically released when the transaction commits
}

Real-World Example: Daily Report Generation

Let’s implement a practical example where multiple application instances need to coordinate daily report generation:

@Component
@RequiredArgsConstructor
@Slf4j
public class DailyReportService {
    private final LockService lockService;
    private final ReportRepository reportRepository;
    private final NotificationService notificationService;

    @Scheduled(cron = "0 0 2 * * *") // Run at 2 AM daily
    @Transactional
    public void generateDailyReport() {
        String today = LocalDate.now().toString();
        String lockName = "daily-report-" + today;
        Optional<DistributedLock> lock = lockService.tryAcquire(lockName);
        if (lock.isPresent()) {
            try (DistributedLock distributedLock = lock.get()) {
                log.info("Starting daily report generation for {}", today);

                // Check if report already exists (additional safety)
                if (reportRepository.existsByDate(today)) {
                    log.info("Report for {} already exists, skipping", today);
                    return;
                }
 
                // Generate the report
                Report report = generateReport(today);
                reportRepository.save(report);
 
                // Send notifications
                notificationService.sendReportGeneratedNotification(report);
                log.info("Daily report for {} generated successfully", today);
            }
        } else {
            log.info("Daily report for {} is being generated by another instance", today);
        }
    }

    private Report generateReport(String date) {
        // Implementation of report generation logic
        return new Report(date, collectDailyMetrics());
    }
}

Advanced Patterns

1. Lock with Timeout Handling

For blocking locks, you can implement timeout handling using Spring’s @Transactional timeout:

@Transactional(timeout = 30) // 30-second timeout
public void processWithTimeout(String taskId) {
    try (DistributedLock lock = lockService.acquire("timeout-task-" + taskId)) {
        performLongRunningOperation(taskId);
    } catch (DataAccessException e) {
        log.error("Failed to acquire lock within timeout period", e);
        throw new LockTimeoutException("Could not acquire lock for task: " + taskId);
    }
}

2. Hierarchical Locking

Create hierarchical locks for complex operations:

@Transactional
public void processOrderWithHierarchy(String customerId, String orderId) {
    // First acquire customer-level lock
    try (DistributedLock customerLock = lockService.acquire("customer-" + customerId)) {
        // Then acquire order-level lock
        try (DistributedLock orderLock = lockService.acquire("order-" + orderId)) {
            processOrderSafely(customerId, orderId);
        }
    }
}

3. Conditional Processing with Fallback

@Transactional
public ProcessingResult processWithFallback(String taskId) {
    Optional<DistributedLock> lock = lockService.tryAcquire("primary-task-" + taskId);
    if (lock.isPresent()) {
        try (DistributedLock distributedLock = lock.get()) {
            return performPrimaryProcessing(taskId);
        }
    } else {
        // Primary processing is happening elsewhere, perform alternative action
        return performAlternativeProcessing(taskId);
    }
}

Configuration and Best Practices

1. Database Configuration

Ensure your PostgreSQL database is properly configured for advisory locks:

-- Check current lock status
SELECT * FROM pg_locks WHERE locktype = 'advisory';
-- Set appropriate connection and statement timeouts
SET statement_timeout = '30s';
SET lock_timeout = '10s';

2. Spring Configuration

Configure your PostgresLockService bean:

@Configuration
public class LockConfiguration {
    @Bean
    public LockService lockService(JdbcTemplate jdbcTemplate) {
        return new PostgresLockService(jdbcTemplate);
    }
}

Key Benefits and Considerations

Benefits:

  • Cluster-safe: Works across multiple JVM instances
  • Transactional: Automatically releases locks on transaction completion
  • Lightweight: No additional infrastructure required
  • Reliable: Leverages PostgreSQL’s proven lock mechanisms
  • Flexible: Supports both blocking and non-blocking approaches

Considerations:

  • Database dependency: Requires PostgreSQL database connection
  • Transaction requirement: Locks must be used within database transactions
  • Lock key collision: Different lock names with same hash could collide
  • Connection pooling: Consider impact on database connection pools

Conclusion

PostgreSQL advisory locks provide a robust foundation for implementing cluster-safe once-only methods in Java applications. The lock-postgres utility simplifies this implementation by providing a clean API that integrates seamlessly with Spring’s transaction management.

By using these distributed locks, you can ensure that critical operations execute exactly once across your entire cluster, preventing data inconsistencies and duplicate processing. The transaction-based approach ensures that locks are automatically cleaned up, even in failure scenarios, making your distributed system more reliable and maintainable.

Whether you’re processing financial transactions, generating reports, or coordinating data migrations, PostgreSQL advisory locks offer a battle-tested solution for distributed coordination without the complexity of additional infrastructure components.

Using AWS Cognito, API Gateway and Spring Cloud Function Lambda for security authorisation.

This article explains using our OSS lambda-utilities to configure a spring cloud function java lambda to allow method level authorisation using API Gateway and Cognito.

See our OSS repository here.

Architecture Overview

The security setup integrates three key AWS services:

  1. AWS Cognito – Identity provider and JWT issuer
  2. AWS API Gateway – HTTP API with JWT authorizer
  3. AWS Lambda – Function execution environment

Key Components

1. ApiGatewayResponseDecoratorFactory

This is the central factory that creates decorated Spring Cloud Functions with security and error handling:

@Service
public class ApiGatewayResponseDecoratorFactory {
// Creates decorated functions that handle security, errors, and responses
public <Input, Output> Function<Input, APIGatewayV2HTTPResponse> create(Function<Input, Output> function)
}

Purpose:

  • Wraps your business logic functions
  • Automatically handles authentication extraction from API Gateway events
  • Converts exceptions to proper HTTP responses
  • Manages Spring Security context

2. Security Configuration Setup

The security is configured through : AwsCloudFunctionSpringSecurityConfiguration

@EnableMethodSecurity
@Configuration
@Import({LimeJacksonJsonConfiguration.class, ApiGatewayResponseDecoratorFactory.class})
@ComponentScan(basePackageClasses = ApiGatewayAuthenticationMapper.class)
public class AwsCloudFunctionSpringSecurityConfiguration

This enables:

  • Method-level security (@PreAuthorize@Secured, etc.)
  • Automatic authentication mapping
  • Exception handling for security violations

3. Authentication Flow

The authentication process works as follows:

  1. API Gateway receives request with JWT token in Authorization header
  2. JWT Authorizer validates the token against Cognito
  3. API Gateway forwards the validated JWT claims in the request context
  4. extracts authentication from the event: 
    • Reads JWT claims from request context
    • Creates object ApiGatewayAuthentication
    • Maps Cognito groups to Spring Security authorities
    ApiGatewayAuthenticationMapper
  5. Spring Security context is populated for method-level security

AWS Infrastructure Setup

API Gateway Configuration

# Example CDK/CloudFormation for HTTP API with JWT Authorizer
HttpApi:
Type: AWS::ApiGatewayV2::Api
Properties:
Name: MySecureApi
ProtocolType: HTTP

JwtAuthorizer:
Type: AWS::ApiGatewayV2::Authorizer
Properties:
ApiId: !Ref HttpApi
AuthorizerType: JWT
IdentitySource:
- $request.header.Authorization
JwtConfiguration:
Audience:
- your-cognito-client-id
Issuer: https://cognito-idp.{region}.amazonaws.com/{user-pool-id}

Route:
Type: AWS::ApiGatewayV2::Route
Properties:
ApiId: !Ref HttpApi
RouteKey: POST /secure-endpoint
Target: !Sub integrations/${LambdaIntegration}
AuthorizerId: !Ref JwtAuthorizer
AuthorizationType: JWT

Cognito Configuration

UserPool:
Type: AWS::Cognito::UserPool
Properties:
UserPoolName: MyAppUsers
Schema:
- Name: email
AttributeDataType: String
Required: true
Policies:
PasswordPolicy:
MinimumLength: 8

UserPoolClient:
Type: AWS::Cognito::UserPoolClient
Properties:
UserPoolId: !Ref UserPool
ClientName: MyAppClient
GenerateSecret: false
ExplicitAuthFlows:
- ADMIN_NO_SRP_AUTH
- USER_PASSWORD_AUTH

Implementation Example

1. Create Your Business Function

@Component
public class SecureBusinessLogic {

public String processSecureData(MyRequest request) {
// Your business logic here
return "Processed: " + request.getData();
}
}

2. Create the Lambda Handler

@Configuration
@Import(LimeAwsLambdaConfiguration.class)
public class LambdaConfiguration {

@Autowired
private ApiGatewayResponseDecoratorFactory decoratorFactory;

@Autowired
private SecureBusinessLogic businessLogic;

@Bean
public Function<APIGatewayV2HTTPEvent, APIGatewayV2HTTPResponse> secureFunction() {
return decoratorFactory.create(event -> {
// Extract request body
MyRequest request = parseRequest(event.getBody());

// Business logic with automatic security context
return businessLogic.processSecureData(request);
});
}
}

3. Add Method-Level Security

@Component
public class SecureBusinessLogic {

@PreAuthorize("hasAuthority('ADMIN')")
public String processAdminData(MyRequest request) {
return "Admin processed: " + request.getData();
}

@PreAuthorize("hasAuthority('USER') or hasAuthority('ADMIN')")
public String processUserData(MyRequest request) {
return "User processed: " + request.getData();
}
}

4. Access Current User Context

@Bean
public Function<APIGatewayV2HTTPEvent, APIGatewayV2HTTPResponse> contextAwareFunction() {
return decoratorFactory.create(event -> {
// Access current authentication
ApiGatewayContext context = decoratorFactory.getCurrentApiGatewayContext();
ApiGatewayAuthentication auth = context.getAuthentication();

if (auth.isAuthenticated()) {
String username = auth.getPrincipal().getName();
Set<String> groups = auth.getAuthorities()
.stream()
.map(GrantedAuthority::getAuthority)
.collect(Collectors.toSet());

return new UserResponse(username, groups, "Success");
} else {
return new UserResponse("anonymous", Set.of("ANONYMOUS"), "Limited access");
}
});
}

Configuration Properties

The authentication mapper supports several configuration properties:

com:
limemojito:
aws:
lambda:
security:
claimsKey: "cognito:groups" # Cognito groups claim
anonymous:
sub: "ANONYMOUS"
userName: "anonymous"
authority: "ANONYMOUS"

Security Benefits

  1. Automatic JWT Validation: API Gateway validates tokens before reaching Lambda
  2. Claims Extraction: Automatic mapping of Cognito user groups to Spring authorities
  3. Method Security: Use standard Spring Security annotations
  4. Exception Handling: Automatic conversion of security exceptions to HTTP responses
  5. Context Access: Easy access to user information and claims
  6. Anonymous Support: Graceful handling of unauthenticated requests

Error Handling

The decorator automatically handles:

  • Authentication failures → 401 Unauthorized
  • Authorization failures → 403 Forbidden
  • Validation errors → 400 Bad Request
  • General exceptions → 500 Internal Server Error

This architecture provides a robust, scalable security solution that leverages AWS managed services while maintaining clean separation of concerns in your Spring Cloud Function implementation.

Debugging Maven Projects with Conflicting JAR Versions

Maven dependency conflicts are one of the most frustrating issues developers encounter when building Java applications. When multiple versions of the same library exist in your classpath, it can lead to runtime errors, unexpected behavior, and difficult-to-debug issues. This article provides a comprehensive guide to identifying, understanding, and resolving JAR version conflicts in Maven projects.

Understanding Dependency Conflicts

What Are Dependency Conflicts?

Dependency conflicts occur when your project’s dependency tree contains multiple versions of the same artifact (same groupId and artifactId but different versions). Maven’s dependency resolution mechanism will choose one version based on its rules, but this choice might not be compatible with all parts of your application.

Common Symptoms

  • ClassNotFoundException or NoClassDefFoundError at runtime
  • NoSuchMethodError or AbstractMethodError
  • IncompatibleClassChangeError
  • Unexpected behavior in libraries that worked in isolation
  • Different behavior between development and production environments

Identifying Conflicts

1. Using Maven Dependency Plugin

The most effective way to identify conflicts is using Maven’s built-in dependency plugin:

mvn dependency:tree

This command shows your complete dependency tree. Look for multiple versions of the same artifact:

[INFO] +- com.fasterxml.jackson.core:jackson-core:jar:2.13.0:compile
[INFO] +- com.fasterxml.jackson.core:jackson-databind:jar:2.13.0:compile
[INFO] |  \- com.fasterxml.jackson.core:jackson-core:jar:2.12.0:compile (omitted for conflict with 2.13.0)

2. Analyzing Conflicts with Verbose Output

For more detailed conflict analysis:

mvn dependency:tree -Dverbose

This shows which dependencies are omitted due to conflicts and why Maven chose specific versions.

3. Using the Dependency Analyze Goal

mvn dependency:analyze

This command identifies:

  • Used undeclared dependencies
  • Unused declared dependencies
  • Potential conflicts

4. IDE-Based Analysis

Most modern IDEs provide visual dependency analysis:

  • IntelliJ IDEA: Right-click on pom.xml → Analyze Dependencies
  • Eclipse: Project Properties → Java Build Path → Libraries → Maven Dependencies

Understanding Maven’s Resolution Strategy

Maven uses these rules to resolve conflicts:

  1. Nearest Definition: Dependencies closer to the root in the dependency tree win
  2. First Declaration: If dependencies are at the same depth, the first one declared wins
  3. Version Range: Explicit version ranges override transitive dependencies

Resolution Strategies

1. Explicit Dependency Declaration

The most straightforward approach is to explicitly declare the version you want:

<dependencies>    
  <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.13.0</version>
  </dependency>
</dependencies>

2. Dependency Management Section

Use the <dependencyManagement> section to centrally manage versions:

<dependencyManagement>    
  <dependencies>        
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId> 
      <version>2.13.0</version>   
    </dependency>
  </dependencies>
</dependencyManagement>

3. Excluding Transitive Dependencies

Exclude problematic transitive dependencies:

<dependency>    
  <groupId>org.springframework</groupId>  
  <artifactId>spring-web</artifactId>   
  <version>5.3.0</version>  
  <exclusions>
     <exclusion>     
        <groupId>com.fasterxml.jackson.core</groupId>       
        <artifactId>jackson-core</artifactId>  
        </exclusion>  
     </exclusions>
</dependency>

4. Using Maven Enforcer Plugin

Prevent conflicts by failing the build when they occur:

<plugin>    
  <groupId>org.apache.maven.plugins</groupId> 
  <artifactId>maven-enforcer-plugin</artifactId>
  <version>3.0.0</version> 
  <executions>       
    <execution>
       <id>enforce-no-duplicate-dependencies</id>        
       <goals>            
         <goal>enforce</goal>       
       </goals>  
       <configuration>       
          <rules>                
            <dependencyConvergence/>        
            <requireNoRepositories/>           
          </rules>  
       </configuration>   
     </execution>
   </executions>
</plugin>

Advanced Debugging Techniques

1. Creating a Dependency Report

Generate detailed dependency reports:

mvn project-info-reports:dependencies

This creates an HTML report showing all dependencies and their relationships.

2. Using Maven’s Debug Output

Run Maven with debug output to see detailed resolution information:

mvn -X dependency:tree

3. Checking Effective POM

View the effective POM to see resolved dependencies:

mvn help:effective-pom

Best Practices

1. Use Bill of Materials (BOM)

Import BOMs for consistent dependency versions:

<dependencyManagement>  
  <dependencies>       
    <dependency>       
      <groupId>org.springframework.boot</groupId>    
      <artifactId>spring-boot-dependencies</artifactId>      
      <version>2.7.0</version>     
      <type>pom</type>      
      <scope>import</scope>      
    </dependency>    
  </dependencies>
</dependencyManagement>

2. Regular Dependency Updates

Keep dependencies up to date and use tools like:

  • mvn versions:display-dependency-updates
  • mvn versions:use-latest-releases

3. Minimize Direct Dependencies

Reduce the number of direct dependencies to minimize conflict opportunities.

4. Use Dependency Scopes Appropriately

  • compile: Default scope
  • provided: Available at compile time but not packaged
  • runtime: Not needed for compilation but required at runtime
  • test: Only available during testing

Preventing Future Conflicts

1. Establish Dependency Governance

  • Create a team-wide dependency management strategy
  • Use parent POMs for version consistency
  • Regular dependency audits

2. Automated Conflict Detection

Integrate conflict detection into your CI/CD pipeline:

<plugin>    <groupId>org.apache.maven.plugins</groupId>    <artifactId>maven-dependency-plugin</artifactId>    <executions>        <execution>            <goals>                <goal>analyze-only</goal>            </goals>            <configuration>                <failOnWarning>true</failOnWarning>            </configuration>        </execution>    </executions></plugin>

3. Version Range Strategy

Be cautious with version ranges. Prefer specific versions for stability:

<!-- Avoid --><version>[1.0,2.0)</version>
<!-- Prefer --><version>1.5.2</version>

Common Conflict Scenarios

Spring Framework Conflicts

Spring projects often have complex dependency trees. Use Spring Boot’s dependency management or Spring Framework BOM.

Logging Framework Conflicts

Multiple logging frameworks (Log4j, Logback, Commons Logging) often conflict. Use SLF4J as a facade and bridge other frameworks.

Jackson Library Conflicts

Jackson modules must use compatible versions. Manage them centrally in dependencyManagement.

Conclusion

Debugging Maven dependency conflicts requires a systematic approach:

  1. Identify conflicts using Maven tools
  2. Understand Maven’s resolution strategy
  3. Apply appropriate resolution techniques
  4. Prevent future conflicts with good practices

The key is to be proactive rather than reactive. Establish good dependency management practices early in your project lifecycle, and use automated tools to catch conflicts before they reach production.

Remember that dependency conflicts are often symptoms of deeper architectural issues. Sometimes the best solution is to refactor your application to reduce complex dependency chains rather than working around conflicts with exclusions and forced versions.

By following these practices and using the tools outlined in this article, you’ll be well-equipped to handle even the most complex dependency conflict scenarios in your Maven projects.

AWS unit testing with LocalStack, Docker and Java

Traditionally unit testing is performed with a class being injected with mocks for its dependencies, so testing is focused just on the behaviours of the class under consideration.

Figure 1: Unit Test class responsibilities

While this is effective for “simple” dependent APIs that may only have a few behaviours, for complex resources such as databases, web service APIs such as DynamoDB, etc it can make sense to unit test using a “fast” implementation of the real resource. By “fast” here we mean quick to setup and tear down so that we can concentrate our effort on the behaviours of the class being tested.

Modern development is tied closely to cloud native APIs such as AWS. We can use a “fast” stub of AWS service with LocalStack deployed on docker. This gives us in memory, localhost based AWS services for most of the available APIs.

Figure 2: LocalStack Unit Test for AWS resources

How to do this using Java and Maven

Using our oss-maven-standards build system we have enabled optional Docker style unit testing using Surefire under Maven. An example layout with docker compose configuration, etc can be seen in the java-lambda-poc module.

Use the any of our parent POMs as your maven archetype.

Set your pom.xml’s parent to one of our archetypes to get docker support. For example, when building a java lambda:

<parent>
    <groupId>com.limemojito.oss.standards</groupId>
    <artifactId>java-lambda-development</artifactId>
    <version>15.2.7</version>
    <relativePath/>
</parent>

Enable docker for unit test mode

This is done in the properties section of the pom.xml

<properties>
   ...
   <!-- Test docker unit test... -->
   <docker.unit.test>true</docker.unit.test>
   ...
</properties>

For Spring Boot testing, set active profile to “integration-test”

We are using our S3Support test utilities to build a set of S3 resources around our unit test. These automatically configure LocalStack when the configuration is imported as below.

@ActiveProfiles("integration-test")
@SpringBootTest(classes = S3SupportConfig.class)
public class S3DockerUnitTest {

    @Autowired
    private S3Support s3;

Write your unit test

Now we can write a unit test that is backed by LocalStack’s S3 implementation in docker when the test runs:

    @Test
    public void shouldDoThingsWithS3AsAUnitTest() {
        s3.putData(s3Uri, "text/plain", "hello world".getBytes(UTF_8));
        assertThat(s3.keyExists(s3Uri)).withFailMessage("Key %s is missing", s3Uri)
                                       .isTrue();
    }

Full Source Example

https://github.com/LimeMojito/oss-maven-standards/tree/master/development-test/jar-lambda-poc

Surprise: AWS SnapStart needs a new image

When using AWS SnapStart to optimise our Java Lambdas, we’ve noticed an interesting caveat:

If the lambda is not invoked for a long period of time (say a week) then the snapshot image is discarded. The next invocation will generate a new image.

While this is not an issue for a lambda endpoint with some volume, for low volume lambdas, such as site where New User Onboarding may be rare, this means that the user experience may be poor as there could be a two minute delay on the invocation! In our situation we had a five second timeout on the call so this breaks immediately.

How do we work around this?

  • Keep the lambda version hot with pre-provisioning of 1 (see Pre-provisioning concurrency). This has an AWS cost based on your lambda memory settings.
  • “Nudge” the lambda by invoking it once a day on a timer. This has an AWS cost but only one invocation.
  • “Tie” the lambda image to another behaviour with higher volume by using lambda based routing. As the higher volume invokes the image more often, snapshot staleness doesn’t occur.
  • Replace the Java lambda with Javascript / python etc that has a lower cold start time.

Keeping a lambda SnapStart image hot with pre-provisioning

Adjust your deployment to set pre-provisioned concurrency to at least 1. Be aware that you will be charged for the lambda execution as if the lambda was running for the provisioned time.

Consider an ARM (cheaper) 1GB lambda provisioned for one day in us-west-2 (Oregon)

$0.0000033334 for every GB-second x 60 x 60 x 24
= 0.0000033334 x 86400
= USD $0.288 per day
= USD $105.12 per year

Plus execution time costings for actual invocation.

Keeping a lambda SnapStart image hot with a timer

Adjust your deployment by creating a CloudWatch event to invoke your lambda once a day. This tutorial, while focusing on Javascript, is applicable for the CloudWatch setup to invoke the Java lambda.

Note the response can be ignored, we are simply invoking so that the image remains hot. An example AWS cost of for an ARM (cheaper) 1GB lambda provisioned in us-west-2 (Oregon) with a 250ms execution time:
$0.0000000133 for every GB ms x 250
= USD $0.0000033250 per day
= USD $0.00123 per year

This may also be within the “free tier” for lambda invocations depending on your site traffic.

For an example using Java CDK: See our OSS example here.

“Tying” Lambda images together

In our scenario, we have a User Group Calculation lambda that is called at the session start for all logged in users that has a similar library and construction to the New User Onboarding. Given the volume of the User Group Calculation the image never becomes stale.

We adjust our deployment configuration so that the entry points for the User Group Calculation and the New User Onboarding point to the same Lambda image. That lambda implementation switches between the two functions based on the request event structure.

At the cost of moving routing into the implementation, we have tied the high volume and low volume calls so that the share image never becomes stale.

Replacing Java SnapStart lambda implementation

Another option is to replace the low volume Java lambda with interpreted code that will not suffer from the SnapStart image staleness. A Javascript lambda would be lighter weight, and if the lambda code is not too complex it could be crafted without middle wares to speed lambda time.

However this introduces more of a polyglot language approach, which we wanted to avoid as we have a lot of in house libraries that speed our Java development.

Conclusion

For our start-up software we decided to use the day timer as the AWS cost was trivial and we could apply a standard approach into our CDK module for lambda deployment.

Beware low volume Java lambdas and SnapStart.

Optimising AWS SnapStart and Spring Boot Java Lambdas

This article looks at optimising a Java Spring Boot application (Cloud Function style) with AWS SnapStart, and covered advanced optimisation with lifecycle management of pre snapshots and post restore of the application image by AWS SnapStart. We cover optimising a lambda for persistent network connection style conversational resources, such as an RDBMS, SQL, legacy messaging framework, etc.

How Snap Start Works

To import start up times for a cold start, SnapStart snapshots a virtual machine and uses the restore of the snapshot rather than the whole JVM + library startup time. For Java applications built on frameworks such as Spring Boot, this provides order of magnitude time reductions on cold start time. For a comparison with raw, SnapStart and Graal Native performance see our article here.

What frameworks do we use with Spring Boot?

For our Java Lambdas we use Spring Cloud Function with the AWS Lambda Adaptor. For an example for how we set this up, and links to our development frameworks and code, see our article AWS SnapStart for Faster Java Lambdas

Default SnapStart: Simple Optimisation of the Lambda INIT phase

When the lambda version is published SnapStart will run up the Java application to the point that the lambda is initialised. For a spring cloud function application, this will complete the Spring Boot lifecycle to the Container Started phase. In short, all your beans will be constructed, injected and started from a Spring Container perspective.

AWS: Lambda Execution Lifecycle

SnapStart will then snapshot the virtual machine with all the loaded information. When the image is restored, the exact memory layout of all classes and data in the JVM is restored. Thus any data loaded in this phase as part of a Spring Bean Constructor, @PostCreate annotated methods and ContextRefresh event handlers will have been reloaded as part of the restore.

Issues with persistent network connections

Where this breaks down is if you wish to use a “persistent” network connection style resource, such as a RDBMS connection. In this example, usually in a Spring Boot application a Data Source is configured and the network connections initialised pre container start. This can cause significant slow downs when restoring an image, perhaps weeks after its creation, as all the network connections will be broken.

For a self healing data source, when a connection is requested the connection will check, timeout and have to reconnect the connection and potentially start a new transaction for the number of configured connections in the pool. Even if you smartly set the pool size to one, given the single threaded lambda execution model, that connection timeout and reconnect may take significant time depending on network and database settings.

Advanced Java SnapStart: CRaC Lifecycle Management

Project CRaC, Co-ordinated Restore at Checkpoint, is a JVM project that allows responses to the host operating system having a checkpoint pre a snapshot operation, and the signal that a operating system restore has occurred. The AWS Java Runtime supports integration with CRaC so that you can optimise your cold starts even under SnapStart.

At the time of our integration, we used the CRaC library to create a base class that could be used to create a support class that can handle “manual” tailoring of preSnapshot and postRestore events. Newer versions of boot are integrating CRaC support – see here for details.

We have created a base class, SnapStartOptimizer, that can be used to create a spring bean that can respond to preSnapshot and postRestore events. This gives us two hooks into the lifecycle:

  1. Load more data into memory before the snapshot occurs.
  2. Restore data and connections after we are running again.

Optimising pre snapshot

In this example we have a simple Spring Component that we use to exercise some functionality (http based) to load and lazy classes, data, etc. We also exercise the lookup of our spring cloud function definition bean.

@Component
@RequiredArgsConstructor
public class SnapStartOptimisation extends SnapStartOptimizer {

    private final UserManager userManager;
    private final TradingAccountManager accountManager;
    private final TransactionManager transactionManager;

    @Override
    protected void performBeforeCheckpoint() {
        swallowError(() -> userManager.fetchUser("thisisnotatoken"));
        swallowError(() -> accountManager.accountsFor(new TradingUser("bob", "sub")));
        final int previous = 30;
        final int pageSize = 10;
        swallowError(() -> transactionManager.query("435345345",
                                                    Instant.now().minusSeconds(previous),
                                                    Instant.now(),
                                                    PaginatedRequest.of(pageSize)));
        checkSpringCloudFunctionDefinitionBean();
    }
}

Optimising post restore – LambdaSqlConnection class.

In this example we highlight our LambdaSqlConnection class, which is already optimised for SnapStart. This class exercises a delegated java.sql.Connection instance preSnapshot to confirm connectivity, but replaces the connection on postRestore. This class is used to implement a bean of type java.sql.Connection, allowing you to write raw JDBC in lambdas using a single RDBMS connection for the lambda instance.

Note: Do not use default Spring Boot JDBC templates, JPA, Hibernate, etc in lambdas. The overhead of the default multi connection pools, etc is inappropriate for lambda use. For heavy batch processing a “Run Task” ECS image is more appropriate, and does not have 15 minute timeout constraints.

So how does it work?

Instances and interfaces managed by LambdaSqlConnection
  1. The LambdaSqlConnection class manages the Connection bean instance.
  2. When preSnapshot occurs, LambdaSqlConnection closes the Connection instance.
  3. When postRestore occurs, LambdaSqlConnection reconnects the Connection instance.

Because LambdaSqlConnection creating a dynamic proxy as the Connection instance, it can manage the delegated connection “behind” the proxy without your injected Connection instance changing.

Using Our SQL Connection replacement in Spring Boot

See the code at https://github.com/LimeMojito/oss-maven-standards/tree/master/utilities/aws-utilities/lambda-sql.

Maven dependency:

<dependency>
   <groupId>com.limemojito.oss.standards.aws</groupId>
   <artifactId>lambda-sql</artifactId>
   <version>15.0.2</version>
</dependency>

Importing our java.sql.Connection interceptor

@Import(LambdaSqlConnection.class)
@SpringBootApplication
public class MySpringBootApplication {

You can now remove any code that is creating a java.sql.Connection and simply use a standard java.sql.Connection instance injected as a dependency in your code. This configuration creates a java.sql.Connection compatible bean that is optimised with SnapStart and delegates to a real SQL connection.

Configuring your (real) DB connection

Example with Postgres driver.

lime:
  jdbc:
    driver:
      classname: org.postgresql.Driver
    url: 'jdbc:postgresql://localhost:5432/postgres'
    username: postgres
    password: postgres

Example spring bean using SQL

@Service
@RequiredArgsConstructor
public class MyService {
    private final Connection connection;

    @SneakyThrows
    public int fetchCount() {
      try(Statement statement = connection.createStatement()){
         try(ResultSet results = statement.executeQuery("count(1) from some_table")) {
             results.next();
             results.getInt(1);
         }
      }
    }
}

References

Deploying Java Lambda with Localstack

We deploy and debug our Java Lambda on development machines using Localstack to emulate and Amazon Web Services (AWS) account. This article walks through the architecture, deployment using our open source java framework to local stack and enabling a debug mode for remote debugging using any Java integrated development environment (IDE).

These capabilities live in our test-utilities module, LambdaSupport.java.

Localstack development architecture

Our build framework uses Docker to deploy a Localstack image, then we use AWS Api calls to deploy a zip of our lambda java classes to the Localstack lambda engine. Due to the size of the zip files, we need to deploy the lambda using a S3 url. We use Localstack’s S3 implementation to emulate the process.

When the lambda is deployed, the Localstack Lambda engine will pull the AWS Lambda Runtime image from public ECR and then perform the deployment steps. Using the Localstack endpoint for lambda we now have a full environment where we can perform a lambda.invoke to test the deployed function.

Figure 1: Development architecture using Localstack for lambda deployment

Viewing lambda logs

With the appropriate Localstack configuration we can view lambda logs for both startup and run of the lambda. Note these logs appear in the docker logs for the AWS Lambda Runtime Container. This container spins up when the lambda is deployed.

The easiest method we use to see the logs is to:

  1. Run the Junit test in debug, with a breakpoint after the lambda invoke.
  2. When the breakpoint is hit, use docker ps and docker logs to see the output of the Lambda Runtime.
  3. In IntelliJ Ultimate, you can see the containers deployed via the Services pane after connecting to your docker daemon.

Using the architecture in debug mode

We can use this architecture to remote debug the deployed lambda. Our LambdaSupport class includes configuration on deploy to enable debug mode as per the Localstack documentation https://docs.localstack.cloud/user-guide/lambda-tools/debugging/. With our support class you simply switch from java() to javaDebug() and the deploy will configure the runtime for debug mode (port 5050 by default).

In your docker-compose.yml, set the environment variable LAMBDA_DOCKER_FLAGS=-p 127.0.0.1:5050:5050 -e LS_LOG=debug.

This enables port passthrough for the java debugger from localhost to port 5050 of the container (assuming that is where the JVM debugging is configured for).

Do not commit this code as it will BLOCK test threads until a debugger is connected (port 5050 by default).

Figure 2: Localstack Java Lambda debug architecture

References:

Code examples

See https://github.com/LimeMojito/oss-maven-standards/blob/master/development-test/jar-lambda-poc/src/test/java/ApplicationIT.java for a full example.

Adding test-utilities to your maven project

These are included by default if you use our jar-lambda-development parent POM.

See our post about using our build system for maven.

Otherwise you can manually add the support as below (version omitted),

<dependency>
    <groupId>com.limemojito.oss.test</groupId>
    <artifactId>test-utilities</artifactId>
    <scope>test</scope>
</dependency>
<dependency>
    <!-- Access for LambdaSupport -->
    <groupId>software.amazon.awssdk</groupId>
    <artifactId>lambda</artifactId>
    <scope>test</scope>
</dependency>
<dependency>
    <!-- Access for LambdaSupport -->
    <groupId>software.amazon.awssdk</groupId>
    <artifactId>s3</artifactId>
    <scope>test</scope>
</dependency>

Loading the lambda as a static variable in a unit test.

We recommend a static initialised once a junit setup function due to the time to deploy the lambda.

The LambdaSupport.java method performs deployment of the supplied module zip to Localstack S3, then invokes the AWS Lambda API to confirm that the lambda has started cleanly (state == Active).

private static Lambda LAMBDA;
...
// environment variables for the lambda configuration
final Map<String, String> environment = Map.of(
                    "SPRING_PROFILES_ACTIVE", "integration-test"
                    "SPRING_CLOUD_FUNCTION_DEFINITION","get"
            );
// using the lambda zip that was built in module ../jar-lambda-poc
LAMBDA = lambdaSupport.java("../jar-lambda-poc",
                            LimeAwsLambdaConfiguration.LAMBDA_HANDLER,
                            environment);

Invoking the lambda for black box testing

This example is using a static variable for the Lambda, JUnit 5 and assert4J. An AWS API Gateway event JSON is loaded and invoked to the deployed lambda. The result is asserted.

Full example is in our oss-maven-standards repository as in integration test (IT, run by failsafe).

@Test
public void shouldCallTransactionPostOkApiGatewayEvent() {
    final APIGatewayV2HTTPEvent event = json.loadLambdaEvent("/events/postApiEvent.json",
                                                             APIGatewayV2HTTPEvent.class);

    final APIGatewayV2HTTPResponse response = lambdaSupport.invokeLambdaEvent(LAMBDA,
                                                                              event,
                                                                              APIGatewayV2HTTPResponse.class);

    assertThat(response.getStatusCode()).isEqualTo(200);
    String output = json.parse(response.getBody(), String.class);
    assertThat(output).isEqualTo("world");
}

Localstack lambda deployment debug example

We alter the setup to use the deprecated javaDebug function. Do not commit this code as it will BLOCK test threads until a debugger is connected (port 5050 by default).

For a clean setup in Intelij that waits for the lambda to start in debug mode, see the excellent article on Localstack https://docs.localstack.cloud/user-guide/lambda-tools/debugging/ “Configuring IntelliJ IDEA for remote JVM debugging”.

// using the lambda zip that was built in module ../jar-lambda-poc
LAMBDA = lambdaSupport.javaDebug("../jar-lambda-poc",
                                 LimeAwsLambdaConfiguration.LAMBDA_HANDLER,
                                 environment);

Maintainable builds – with Maven!

Maven is known to be a verbose, opinionated framework for building applications, primarily for a Java Stack. In this article we discuss Lime Mojito’s view on maven, and how we use it to produce maintainable, repeatable builds using modern features such as automated testing, AWS stubbing (LocalStack) and deployment. We have OSS standards you can use in your own maven builds at https://bitbucket.org/limemojito/oss-maven-standards/src/master/ and POM’s on maven central.

Before we look at our standards, we set the context of what drives our build design by looking at our technology choices. We’ll cover why our developer builds are setup this way, but not how our Agile Continuous Integration works in this post.

Lime Mojito’s Technology Choices

Lime Mojito uses a Java based technology stack with Spring, provisioned on AWS. We use AWS CDK (Java) for provisioning and our lone exception is for web based user interfaces (UI), where we use Typescript and React with Material UI and AWS Amplify.

Our build system is developer machine first focused, using Maven as the main build system for all components other than the UI.

Build Charter

  • The build enforces our development standards to reduce the code review load.
  • The build must have a simple developer interface – mvn clean install.
  • If the clean install passes – we can move to source Pull Request (PR).
    • PR is important, as when a PR is merged we may automatically deploy to production.
  • Creating a new project or module must not require a lot of configuration (“xml hell”).
  • A module must not depend on another running Lime Mojito module for testing.
  • Any stub resources for testing must be a docker image.
  • Stubs will be managed by the build process for integration test phase.
  • The build will handle style and code metric checks (CheckStyle, Maven Enforcer, etc) so that we do not waste time in PR reviews.
  • For open source, we will post to Maven Central on a Release Build.

Open Source Standards For Our Maven Builds

Our very “top” level of build standards is open source and available for others to use or be inspired by:

Bitbucket: https://bitbucket.org/limemojito/oss-maven-standards/src/master/

The base POM files are also available on the Maven Central Repository if you want to use our approach in your own builds.

https://repo.maven.apache.org/maven2/com/limemojito/oss/standards/

Maven Example pom.xml for building a JAR library

This example will do all the below with only 6 lines of extra XML in your maven pom.xml file:

  • enforce your dependencies are a single java version
  • resolve dependencies via the Bill of Materials Library that we use too smooth out our Spring + Spring Boot + Spring Cloud + Spring Function + AWS SDK(s) dependency web.
  • Enable Lombok for easier java development with less boilerplate
  • Configure code signing
  • Configure maven repository deployment locations (I suggest overriding these for your own deployments!)
  • Configure CheckStyle for code style checking against our standards at http://standards.limemojito.com/oss-checkstyle.xml
  • Configure optional support for docker images loading before integration-test phase
  • Configure Project Lombok for Java Development with less boilerplate at compile time.
  • Configure logging support with SLF4J
  • Build a jar with completed MANIFEST.MF information including version numbers.
  • Build javadoc and source jars on a release build
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>my.dns.reversed.project</groupId>
    <artifactId>my-library</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <parent>
        <groupId>com.limemojito.oss.standards</groupId>
        <artifactId>jar-development</artifactId>
        <version>13.0.4</version>
        <relativePath/>
    </parent>
</project>

When you add dependencies, common ones that are in or resolved via our library pom.xml do not need version numbers as they are managed by our modern Bill of Materials (BOM) style dependency setup.

Example using the AWS SNS sdk as part of the jar:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>my.dns.reversed.project</groupId>
    <artifactId>my-library</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <parent>
        <groupId>com.limemojito.oss.standards</groupId>
        <artifactId>jar-development</artifactId>
        <version>13.0.4</version>
        <relativePath/>
    </parent>

    <dependencies>
        <dependency>
            <groupId>software.amazon.awssdk</groupId>
            <artifactId>sns</artifactId>
        </dependency>
    </dependencies>
</project>

Our Open Source Standards library supports the following module types (archetypes) out of the box:

TypeDescription
java-developmentBase POM used to configure deployment locations, checkstyle, enforcer, docker, plugin versions, profiles, etc. Designed to be extended for different archetypes (JAR, WAR, etc.).
jar-developmentBuild a jar file with test and docker support
jar-lamda-developmentBuild a Spring Boot Cloud Function jar suitable for lambda use (java 17 Runtime) with AWS dependencies added by default. Jar is shaded for simple upload.
spring-boot-developmentSpring boot jar constructed with the base spring-boot-starter and lime mojito aws-utilities for local stack support.
Available Module Development Types

We hope that you might find these standards interesting to try out.

CPU Throttling – Scale by restricting work

We have a web service responding to web requests. The service has a thread pool where each web request uses one operating system thread. The requests are then managed by a multi-core CPU that time-slices between the various threads using the operating system scheduler.

This example is very similar to how Tomcat (Spring Boot MVC) works out of the box when servicing requests with servlets in the Java web server space. The Java VM (v17) matches a Java Thread to an operating system thread that is then scheduled for execution by a core.

So what happens when we have a lot of requests?

Many threads here are sliced between the 4 cores. This slicing of threads where a core works on one for a while, then context switches to another thread, can scale to any level. However, there is an expense in CPU time to switch between one thread to another. This context switch is expensive as it involves both memory and CPU manipulation.

Given enough threads, the CPU cores can quickly spend a significant amount of time context switching when compared to the actual amount of time processing the request.

How do we reduce context switching?

We can trade off context switching for latency by blocking a request thread until a vCPU is available to do the work. Provided the work is largely CPU bound this may reduce the overall throughput time if the context switching has become a major use of the available vCPU resources.

For our Java spring boot based application we introduce one of the standard Executors to provide a blocking task service. We use a WorkStealingPool which is an executor that defaults the worker threads to the number of CPUs available with an unlimited queue depth.

We now move the CPU heavy process into a task that can be scheduled onto the executor by a given thread. The thread will then block on the Future returned from submitting the task – this blocking occurs until a worker thread has completed the task’s job and returned a result.

On our application, this returned a 5X improvement to average throughput times for the same work being submitted to a single microservice performing the request processing. This goes to show that in our situation the majority of CPU was being spent on context switching between requests rather than servicing the CPU intensive task for each request.

In our case this translated to 5X less CPU required and a similar reduction in our AWS EC2 costs for this service as we needed less instances provisioned to support the same load.

AWS Snap Start for faster Java Lambda

After finding Native Java Lambda to be too fragile for runtimes we investigated AWS Snap Start to speed up our cold starts for Java Lambda. While not as fast as native, Snap Start is a supported AWS Runtime mode for Lambda and it is far easier to build and deploy compared to the requirements for native lambda.

How does Snap Start Work?

Snap Start runs up your Java lambda in the initialisation phase, then takes a VM snapshot. That snapshot becomes the starting point for a cold start when the lambda initialises, rather than the startup time of your java application.

With Spring Boot this shows a large decrease in cold start time as the JVM initialisation, reflection and general image setup is happening before the first request is sent.

Snap Start is configured by saving a Version of your lambda. This version phase takes the VM snapshot and loads that instead of the standard java runtime initialisation phase. The runtime required is the offical Amazon Lambda Runtime and no custom images are required.

What are the trade offs for Snap Start?

Version Publishing needs to be added to the lambda deployment. The deployment time is longer as that image needs to be taken when the version is published.

VM shared resources may behave differently to development as they are re-hydrated before use in the cold start case. For example DB connection pools will need to fail and reconnect as they be begin at request time in a disconnected state. However see AWS RDS Proxy for this serverless use case.

As at 26th August 2023 SnapStart is limited to the x86 Architecture for Lambda runtimes.

What are the speed differences?

After warm up there was no difference between a hot JVM and the native compiled hello world program. Cold start however showed a marked difference from memory settings of 512MB and higher due to the proportional allocation of more vCPU.

Times below are in milliseconds.

Architecture2565121024
Java506640543514
SnapStart4689.222345.21713.82
Native1002773670
Comparison of Architecture v Lambda Memory Configuration
Graph of Lambda Cold Start timings

At 1GB with have approximately 1 vCPU for the lambda runtime which makes a significant difference to the cold start times. Memory settings higher than 1vCPU had little effect.

While native is over twice as fast as SnapStart the fragility of deployment for lambda and the massive increase in build times and agent CPU requirements due to compilation was un productive for our use cases.

Snap start adds around 3 minutes to deployments to take the version snapshot (on AWS resources) which we consider acceptable compared to the build agent increase that we needed to do for native (6vCPU and 8GB). As we are back to Java and scripting our agents are back down to 2vCPU and 2GB with build times less than 10 minutes.

How do you integrate Snap Start with AWS CDK?

This is a little tricky as there are not specific CDK Function props to enable SnapStart (as at 26th August 2023). With CDK we have to fall back to a cloud formation primitive to enable snap start and then take a version

Code example from out Open Source Spring Boot framework below.

final IFunction function = new Function(this,
                                       LAMBDA_FUNCTION_ID,
                                       FunctionProps.builder()
                                                    .functionName(LAMBDA_FUNCTION_ID)
                                                    .description("Lambda example with Java 17")
                                                    .role(role)
                                                    .timeout(Duration.seconds(timeoutSeconds))
                                                    .memorySize(memorySize)
                                                    .environment(Map.of())
                                                    .code(assetCode)
                                                    .runtime(JAVA_17)
                                                    .handler(LAMBDA_HANDLER)
                                                    .logRetention(RetentionDays.ONE_DAY)
                                                    .architecture(X86_64)
                                                    .build());
CfnFunction cfnFunction = (CfnFunction) function.getNode().getDefaultChild();
cfnFunction.setSnapStart(CfnFunction.SnapStartProperty.builder()
                                                      .applyOn("PublishedVersions")
                                                      .build());
IFunction snapstartVersion = new Version(this,
                                         LAMBDA_FUNCTION_ID + "-snap",
                                         VersionProps.builder()
                                                     .lambda(function)
                                                     .description("Snapstart Version")
                                                     .build());

In CDK because Version and Function both implement IFunction, you can pass a Version to route constructs as below.

String apiId = LAMBDA_FUNCTION_ID + "-api";
HttpApi api = new HttpApi(this, apiId, HttpApiProps.builder()
                                                   .apiName(apiId)
                                                   .description("Public API for %s".formatted(LAMBDA_FUNCTION_ID))
                                                   .build());
HttpLambdaIntegration integration = new HttpLambdaIntegration(LAMBDA_FUNCTION_ID + "-integration",
                                                              snapstartVersion,
                                                              HttpLambdaIntegrationProps.builder()
                                                                                        .payloadFormatVersion(
                                                                                                VERSION_2_0)
                                                                                        .build());
HttpRoute build = HttpRoute.Builder.create(this, LAMBDA_FUNCTION_ID + "-route")
                                   .routeKey(HttpRouteKey.with("/" + LAMBDA_FUNCTION_ID, HttpMethod.GET))
                                   .httpApi(api)
                                   .integration(integration)
                                   .build();

Note in the HttpLambdaIntegration that we pass a Version rather than the Function object. This produces the Cloudformation that links the API Gateway integration to your published Snap Start version of the Java Lambda.

References