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AWS Lambdas in Java, in a TypeScript CDK app

I've always written my CDK stacks in TypeScript because (a) it's a nice, fluent language to use, and (b) I often write my application code in TypeScript, be that a Node.js server or a React / Angular / WebComponents UI, and it makes sense to write my infrastructure-as-code using the same language.

In the past, I've successfully integrated lambda functions written in C# with a TypeScript CDK app, making use of Code Assets to build and package my lambdas at synth time. Here I achieve the same for a Java lambda function.

Commands

Remember to npm ci before running your first command.

  • npm run synth Synthesizes the CloudFormation templates
  • npm run deploy Deploys all resources to your default AWS account/region
  • npm run destroy Destroys all deployed resources
  • npm run clean Deletes the cdk.out directory

Synth

Compilation and bundling of the lambda function (via maven) are performed during the synth step. By default, this is done in a Docker container, which is the most portable solution.

If that doesn't work for you, you can enable local build via context property buildlocal. This can be provided on command-line:

npm run synth -- --context buildlocal=true

Alternatively, you can add it to your cdk.context.json file:

{
  "buildlocal": true
}

Testing Locally

If you have the SAM CLI installed, you can use the following commands to test the stack without needing to deploy to an AWS account. Remember to npm run synth first!

Test the Lambda function

# Invoke the lambda with a test event
npm run sam:lambda run-length-encoder -- -e lambdas/run-length-encoder/events/apigw_1.json

# Expected output:
{"statusCode": 200, "headers": {"Content-Type": "text/plain"}, "body": "a3b5c", "isBase64Encoded": false}

Test the API Gateway endpoint

# Run the HTTP API Gateway locally ...
npm run sam:api

# ... Then hit the endpoint in a separate terminal
curl http://localhost:3000/run-length-encoder -d "aaabbbbbcddeeeeeee"

# Expected output:
a3b5cd2e7

Final Thoughts

It would be quite simple to write an L3 construct based on this stack, but I leave that exercise for another day.

Oh, and I stick by my choice of TypeScript for the CDK code, even when writing lambdas in Java. Have you seen how verbose Java CDK code is? Builder hell, no thank you...