Lambda runtime interface emulator

The rule

The runtime image is built on the AWS Lambda .NET base image, which includes the runtime interface emulator. Running the image locally gives an endpoint that invokes the function exactly as Lambda would. docker-compose.yml maps it to port 7350 and turns sample data on. The image runs GetMovies unless you name another handler. Each function's handler string names the class Lambda Annotations generates for it, and src/Presentation/serverless.template lists them all.

Steps

1. Start it: docker compose up -d --build.

2. Invoke it by posting the request JSON to the emulator:

   curl -X POST http://localhost:7350/2015-03-31/functions/function/invocations \
     -d '{ "query": "global", "offset": 0, "limit": 5 }'

3. To try another function, run the image with its handler string as the command:

   docker build . --target run --tag cleanlambdafunction:local
   docker run --rm -p 7350:8080 -e Database__SeedSampleData=true cleanlambdafunction:local \
     "Presentation::CleanLambdaFunction.Presentation.LambdaFunction.Handler_GetAuthors_Generated::GetAuthors"

4. An HTTP API function (HttpGetMovies, HttpGetAuthors, HttpGetReviews) takes the API Gateway HTTP API payload 2.0 event, not the request record. Run it by its handler string as in step 3 and post the event API Gateway would send. The query string values are strings, as they are on the wire:

   curl -X POST http://localhost:7350/2015-03-31/functions/function/invocations \
     -d '{ "version": "2.0", "routeKey": "GET /movies", "rawPath": "/movies", "queryStringParameters": { "query": "global", "limit": "5" }, "requestContext": { "http": { "method": "GET", "path": "/movies" } } }'

   The answer has statusCode, headers and the JSON body as a string. Header names come back in lower case.

5. Send a request that fails validation, such as { "limit": 0 }, and check the error's errorType and errorMessage. An HTTP API function answers a 400 with content-type: application/problem+json instead, and "limit": "0" in the query string shows it.
6. Read the container's output with docker compose logs function. The runtime's start, invoke and error lines sit between our compact JSON events, one per line, at Debug because compose sets Serilog__MinimumLevel__Default (serilog). Each invocation's trace, metrics and logs also land in the Aspire dashboard at http://localhost:7352, through the collector compose starts beside the function (telemetry).
7. Stop it with docker compose down.

Don't

• Use the emulator in place of tests. Anything you check by hand gets a test (presentation-integration-tests).
• Expose port 7350 beyond your machine. The emulator has no authentication.
• Deploy to try a change. The emulator runs the same image Lambda would.

Check

docker compose up -d --build
curl -fsS -X POST http://localhost:7350/2015-03-31/functions/function/invocations -d '{}'
docker compose down