Add local testing infrastructure with AWS Lambda Runtime Interface Emulator (RIE)

[AntoniaSzecsi]

📬 Issue #, if available:

✍️ Description of changes:

Summary
This PR adds local testing capabilities using the official AWS Lambda Runtime Interface Emulator (RIE), enabling developers to test the Rust runtime libraries in a containerized environment that matches AWS Lambda's runtime.

Changes

• RIE testing infrastructure: New make test-rie command for automated local testing
• Docker setup: Dockerfile.rie with Rust toolchain and RIE pre-installed
• Test handler: Demonstrates runtime functionality using local lambda_runtime crate
• Documentation: Updated README with RIE testing section
• Build automation: Script handles Docker build, compilation, and RIE startup

Usage

make test-rie

🔏 By submitting this pull request

• I confirm that I've ran cargo +nightly fmt.
• I confirm that I've ran cargo clippy --fix.
• I confirm that I've made a best effort attempt to update all relevant documentation.
• I confirm that my contribution is made under the terms of the Apache 2.0 license.

[jlizen]

This seems like a great addition! Thanks for this!

I'd like to see a couple of changes:

• remove test-handler crate, use examples/ instead (ideally dynamically selected based on make, but i'd be happy with just a simple one being hardcoded with a RAEDME note on how to go and change it)
• dockerfile not relying on exclusions but rather inclusions for future maintainability

Non-blocking: Is there any possibility of also throwing this into a github actions workflow (.github folder) so that we can get end to end validation of one of our simpler examples on PR? Currently we wait until merge to run integration tests, which isn't ideal, since they are using real AWS calls. No worries if you don't have time for this, just would be pretty neat.

[AntoniaSzecsi]

Thank you for the feedback and for taking the time to review my changes! I hope this resolves the comments.

I apologise for the long commit, here is the summary of changes:

• Delete test-handler/ directory and .dockerignore file
• Replace 'COPY . /build' with explicit COPY statements
• Add dynamically handler selection based on MakeFile
• Add GitHub Actions workflow for RIE testing

[jlizen]

The refactor looks great. Just need a tweak to the dockerfile to fix the CI failure as mentioned in the comment.

[jlizen]

nice!

[jlizen]

This is a good middle ground for making it turnkey, thanks.

[jlizen]

This is causing CI failures since we don't currently have Cargo.lock checked in (perhaps we should start, that decision predates me maintaining):

#11 [ 6/15] COPY Cargo.toml Cargo.lock /build/
#11 ERROR: failed to calculate checksum of ref 1acf8ebc-766d-4eb7-bec2-c07f6b4097da::cdqmyuggq2sgi9amxlakl71dj: "/Cargo.lock": not found

https://github.com/awslabs/aws-lambda-rust-runtime/actions/runs/17301603573/job/49114895249?pr=1033

Maybe just do COPY Cargo.* to sidestep this issue and be agnostic about whether Cargo.lock is available?

Certainly you could update CI to use cargo-generate-lockfile but that seems kind of annoying.