Background

Endeavouring to scratch (pun intended) an itch, by running an AWS Lambda function, written in Go, in a scratch (so OS-less) container. This repo contains a couple of files

💡 This has been created by an idiot who should rarely be trusted with anything sharper than a butter knife, proceed with caution...

Files 💾

main.go

Rather trivial Go source code that renders some log messages when the Lambda function is invoked. To compile, the following might be reasonably assumed to behave as required:

go env -w GOOS=linux
go env -w GOARCH=amd64 
go mod download
go build -ldflags="-w -s" main.go

Dockerfile

The Dockerfile is deliberately as short and simple as possible. Nuff said?

buildspec.yml

The buildspec.yml file can be used in an AWS CodeBuild project to facilitate a devops approach.

Local Explorification 🧑‍💻

All this was done on macOS...

🛠 setup

export ACCOUNT={12 digit AWS account ID}
export REGION=eu-west-2
export ECR_REPO=go
export FUNCTION_NAME=demo
export FUNCTION_OUTPUT=/tmp/logs-command
export SLEEP=5
aws ecr get-login-password --region ${REGION} | docker login --username AWS --password-stdin ${ACCOUNT}.dkr.ecr.${REGION}.amazonaws.com

The SLEEP is used to force a delay into the process, on occasion the log stream isn't instantly available, so a rather hacky hack, but it works (at least most of the time) 🙃

🤞 build

Assumes docker and dive are installed. The -ldflags="-w -s" linker option removes the symbol table, debug information (-s) and the DWARF symbol table (-w) resulting in an approximate 30% reduction in file size for this binary, the image pushed to ECR is roughly half the size (hat tip).

GOOS=linux GOARCH=amd64 go build -ldflags="-w -s" -o main main.go && echo -n "Build success, provide an image tag version: " && read VERSION || echo "Build failed! 🧨"

docker build --tag ${ACCOUNT}.dkr.ecr.${REGION}.amazonaws.com/${ECR_REPO}:${VERSION} .
docker push ${ACCOUNT}.dkr.ecr.${REGION}.amazonaws.com/${ECR_REPO}:${VERSION}

dive ${ACCOUNT}.dkr.ecr.${REGION}.amazonaws.com/${ECR_REPO}:${VERSION}

aws lambda update-function-code --function-name ${FUNCTION_NAME} --image-uri ${ACCOUNT}.dkr.ecr.${REGION}.amazonaws.com/${ECR_REPO}:${VERSION} --no-cli-pager && aws lambda wait function-updated-v2 --function-name ${FUNCTION_NAME} && echo "Function ${FUNCTION_NAME} updated 👌" || echo "Failed to update ${FUNCTION_NAME} 😱"

A multi-stage Dockerfile can build the same binary, the CGO_ENABLED variable needs to be set with (i.e. go env -w CGO_ENABLED=0).

🏃 run

Assumes jq is installed.

aws lambda invoke --function-name ${FUNCTION_NAME} --payload '{"wibble":"wobble","plop":["plip"],"true":false,"emoji":"🤓"}' --cli-binary-format raw-in-base64-out --no-cli-pager ${FUNCTION_OUTPUT} && eval $(sleep ${SLEEP}; cat ${FUNCTION_OUTPUT} | cut -d\" -f2) | jq '.events[].message' -r | sed -e '/^$/d'; rm ${FUNCTION_OUTPUT}

Possibly Handy Links

• https://docs.aws.amazon.com/lambda/latest/dg/lambda-golang.html
• https://github.com/aws/aws-sdk-go
• https://github.com/aws/aws-lambda-go
• https://docs.aws.amazon.com/lambda/latest/dg/go-image.html
• https://go.dev/doc/install/source#environment
• https://go.dev/learn/
• https://docs.docker.com/develop/develop-images/multistage-build/#name-your-build-stages
• https://chemidy.medium.com/create-the-smallest-and-secured-golang-docker-image-based-on-scratch-4752223b7324