nabeken/go-lambda-subcommands-example repository overview

⁠go-lambda-subcommands-example

This repository is to demonstrate how to build a container image that works with AWS Lambda Container Image Support, especially over a subcommand on the AWS environment and Lambda Runtime Interface Emulator (local).

This demo is build with Go but it may work with any other language.

⁠How it works

The Lambda runtime (/var/runtime/bootstrap) looks up a binary based on _HANDLER environment variable (handler in the configuration). This value is mapped to an executable file under /var/task/. If _HANDLER=main, then the runtime will invoke /var/task/main.

The problem is it cannot invoke a function under a subcommand (e.g. main helloworld). To reduce a size of a container image, especially built with Go, we ship a single binary that can run multiple commands.

For example, I really wanted to maintain a single binary main that can be invoked as Lambda function.

• ./main func1
• ./main func2

There are three parts to make it possible.

entrypoint.sh⁠: This will be invoked via the container runtime with command-line arguments. It will escape the original arguments into a file so that the _lambda_main command, which will be invoked via the Lambda runtime, can invoke a command with the original arguments as a Lambda function.

_lambda_main⁠: The Lambda runtime will invoke this command via _HANDLER. This is a shim for the Lambda runtime to restore an original command-line arguments.

Dockerfile⁠: A sample Dockerfile to build a workable contaienr image.

⁠Run locally

docker build -t local/go-lambda-subcommands-example:latest .
docker run -p 9000:8080 -it --rm local/go-lambda-subcommands-example:latest

# from another terminal
curl -XPOST "http://localhost:9000/2015-03-31/functions/function/invocations" -d '{}'