You are absolutely right that you could recreate a similar environment to Lambda in Docker. But you would first need to reverse engineer Lambda's environment to discover how it is actually configured and the limits that are set.

Even if you did find a way, you would still need to keep it up to date in case AWS decides to update that environment.

Logged in to say that this has actually been done (not by me) and my team has been finding it very helpful for local “serverless” SDLC: https://github.com/lambci/docker-lambda . It‘s billed as “ A sandboxed local environment that replicates the live AWS Lambda environment almost identically – including installed software and libraries, file structure and permissions, environment variables, context objects and behaviors – even the user and running process are the same.” We test our functions mocked and against local deployments of that lambci container . There also lambda “layers” (container images for building custom runtimes for AWS Lambda) but we have not used that feature at this point. Interesting space with lots of room for improvement in this tool chain though for sure

Nice!

I saw that the SAM CLI uses an Alpine based image, does yours use Amazon Linux 2?

I'm jusz asking, because I compiled some libs on Cloud9 (which uses AL) and they worked on Lambda, so I assumed it's the same dist.

I’m not 100% sure as I didn’t create the image (though I’m evangelizing as someone who has found it truly helpful for daily dev.) . I believe the creators tarball’d the entire distro/execution environment from a running lambda so the file system layout and libs likely match Amazon Linux if that’s the default lambda execution distro image. If not I assume it matches the default

At least the Docker image used by AWS SAM CLI is created by AWS.

Also, you compile before packaging, so you dev/CI system already has to be able to compile for Lambda, independenly from testing/debugging with Docker.