Example AWS Lambda function in Go

This repo was created exclusively to answer a specific stackoverflow question

It copies the question's Go code, and shows how to troubleshoot things locally, and how to deploy a function version of the same code in AWS.

Pre-requisites

To run the code in this repo make sure you set up the following dependencies on your machine:

• Go installed
• AWS CDK getting started requisites

Project genesis

For the sake of clarity, here is how this project was bootstrapped by setting up a go environment, and then an AWS CDK project to deploy things in AWS.

Go environment

# setup go code:
mkdir -p lambda && cd lambda
go mod init mklabs.io/golambda
# install dependencies
go get github.com/aws/aws-lambda-go/lambda
touch main.go

.. and copy-pasting the code from this stackoverflow post into main.go file.

Then download locally AWS lambda runtime environment as provided by AWS documentation

mkdir -p ~/.aws-lambda-rie && curl -Lo ~/.aws-lambda-rie/aws-lambda-rie \
  https://github.com/aws/aws-lambda-runtime-interface-emulator/releases/latest/download/aws-lambda-rie \
  && chmod +x ~/.aws-lambda-rie/aws-lambda-rie               

CDK environment

mkdir -p cdk && cd cdk
cdk init sample-app --language typescript

And adjusted the code to create a lambda function and an AWS API Gateway.

Running locally

To test the lambda function locally run:

cd lambda
~/.aws-lambda-rie/aws-lambda-rie go run main.go

This will start a server listening on port 8080. To actually trigger the lambda function, run on a new shell session:

curl -XPOST "http://localhost:8080/2015-03-31/functions/function/invocations" -d '{"Name": "World"}'

On this second shell session you should see the following output as a result:

{"statusCode":200,"headers":null,"multiValueHeaders":null,"body":"hello world"}%                     

Likewise, on the first shell session you should see an output similar to the following:

06 May 2023 18:38:31,456 [INFO] (rapid) exec 'go' (cwd=/home/johndoe/development/go-lambda/lambda, handler=main.go)
06 May 2023 18:38:38,086 [INFO] (rapid) extensionsDisabledByLayer(/opt/disable-extensions-jwigqn8j) -> stat /opt/disable-extensions-jwigqn8j: no such file or directory
START RequestId: 340cd023-ea7f-440d-b0f5-7ad36dd10ba2 Version: $LATEST
06 May 2023 18:38:38,086 [INFO] (rapid) Configuring and starting Operator Domain
06 May 2023 18:38:38,086 [INFO] (rapid) Starting runtime domain
06 May 2023 18:38:38,086 [WARNING] (rapid) Cannot list external agents error=open /opt/extensions: no such file or directory
06 May 2023 18:38:38,087 [INFO] (rapid) Starting runtime without AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_SESSION_TOKEN , Expected?: false
2023/05/06 18:38:38 hello world
END RequestId: bbe82927-68af-45f2-b83f-c14cd79f2eea
REPORT RequestId: bbe82927-68af-45f2-b83f-c14cd79f2eea	Init Duration: 0.08 ms	Duration: 356.12 ms	Billed Duration: 357 ms	Memory Size: 3008 MB	Max Memory Used: 3008 MB

Build a binary

If you need to build a binary:

GOOS=linux GOARCH=amd64 go build -o main .

To execute the binary:

~/.aws-lambda-rie/aws-lambda-rie ./main

Deploying on AWS

We will use AWS CDK for deploying the Lambda function and API Gateway.

If it is the first time running this repo's cdk code, make sure you install all dependencies:

npm install

Before deploying, you can view the generated CloudFormation code by running:

cdk synth

To deploy the assets:

# to view the generated CloudFormation code
cdk deploy

CDK will still provide a list of all resources and prompt for confirmation.

After confirming, you should see at the end of all outputs something similar to the following:

✅  LambdaApiCdkStack

✨  Deployment time: 75.99s

Outputs:
LambdaApiCdkStack.GoLambdaApiEndpoint5E710713 = https://xxxxxxxxxx.execute-api.us-east-1.amazonaws.com/prod/

✨  Total time: 81.1s

You can now curl this endpoint, and should see hello world as an output:

curl https://xxxxxxxxxx.execute-api.us-east-1.amazonaws.com/prod/

Tests

To run unit tests for CDK run:

npm test