Go functions on AWS Lambda in Docker

Uses the following technologies:

• Go programming language
• Docker as container
• AWS Lambda to host the function
• AWS ECR (Elastic Container Registry) to host the Docker image
• AWS API Gateway to expose the Lambda function as a REST API
• AWS CLI tool (aws) to configure AWS

The current setup in this project is: 1 REST endpoint → 1 Lambda function → inside 1 Docker image.

Based on Docker Hub: aws-lambda-go and this example Gist. See also:

• AWS:
  • AWS Deploy Go Lambda functions with Docker
  • AWS Go guide
  • AWS Docker image on ECR (Elastic Container Registry)
  • AWS Lambda on Docker
  • Example of AWS Lambda function written in Go
  • AWS API Gateway tutorial: turn Lambda function into REST API
• Docker:
  • Building Go Docker images
• Other:
  • AWS Lambda in GoLang — The Ultimate Guide

Write your Lambda function in Go

Edit my-lambda-function/main.go

Building both Go binary and Docker image

make

(Optional: Manual build steps for Go binary and Docker image)

Build Go binary

Create the working directory

mkdir my-lambda-function

Change to the directory

cd my-lambda-function

(Create the files: main.go and Dockerfile)

Initialize the module in Go

go mod init example.com/my-lambda-function

Build the go app for Linux

GOOS=linux go build

Build Docker image

To build your Docker image:

docker build -t my-lambda-function .

Running the Lambda function locally

To run your image locally:

docker run -p 9000:8080 my-lambda-function

In a separate terminal, you can then locally invoke the function using cURL:

curl -XPOST "http://localhost:9000/2015-03-31/functions/function/invocations" -d '{"name":"Tom"}'

✅ You should get a response like {"message":"Hello! Dear Tom!"}

Deploy to AWS Lambda

Parameters used below:

• [my-lambda-function]: substitute with your app/repository/image name
• [AWS Account Number]: e.g. 123456789012
• [Region]: e.g. eu-west-1, us-east-1

Create an IAM Policy (e.g. ECRDockerImageCreation) with the following permissions:

ecr:*

You also need an IAM Role (e.g. lambda-ex) for executing the Lambda function.

Build your local Docker image:

make

Create a new Lambda function

Authenticate the Docker CLI to your Amazon ECR registry:

aws ecr get-login-password --region [Region] | docker login --username AWS --password-stdin [AWS Account Number].dkr.ecr.[Region].amazonaws.com

✅ You should get a response like Login Succeeded

Tag your new Docker image to match your repository name:

docker tag [my-lambda-function]:latest [AWS Account Number].dkr.ecr.[Region].amazonaws.com/[my-lambda-function]:latest

(You won’t get any response)

Create an ECR repository:

aws ecr create-repository --repository-name [my-lambda-function] --region [Region]

Deploy the Docker image to Amazon ECR:

docker push [AWS Account Number].dkr.ecr.[Region].amazonaws.com/[my-lambda-function]:latest

You should now see your image repository on https://console.aws.amazon.com/ecr/repositories?region=[Region]

aws lambda create-function --region [Region] --function-name [my-lambda-function] \
  --package-type Image \
  --code ImageUri=[AWS Account Number].dkr.ecr.[Region].amazonaws.com/[my-lambda-function]:latest \
  --role arn:aws:iam::[AWS Account Number]:role/lambda-ex

✅ You can now test your Lambda function in the AWS Console, “Test” tab.

Turn the Lambda function into a REST API using AWS API Gateway

• Go to https://console.aws.amazon.com/apigateway
• REST API → Build
• Select 🔘 “New API”
• Actions → Create Resource, enter resource name e.g. my-lambda-function
• Select your created resource, then Actions → Create Method
• Select method (e.g. POST, or ANY)
• Select Integration type: 🔘 “Lambda Function”, then check the ☑️ “Use Lambda Proxy integration” and enter the name of your function under “Lambda Function”
• Actions → Deploy API
• Enter a “Stage” name e.g. “test”

You will get an endpoint back, e.g. https://12345xw4tf.execute-api.eu-west-1.amazonaws.com/test (note: excludes the function name, see the full curl example below)

✅ You can now test the API with:

curl -XPOST "https://12345xw4tf.execute-api.eu-west-1.amazonaws.com/test/my-lambda-function" -d '{"name":"Tom"}'

Update an existing Lambda function

Tag your new Docker image to match your repository name:

docker tag [my-lambda-function]:latest [AWS Account Number].dkr.ecr.[Region].amazonaws.com/[my-lambda-function]:latest

Deploy the Docker image to Amazon ECR:

docker push [AWS Account Number].dkr.ecr.[Region].amazonaws.com/[my-lambda-function]:latest

Update the Lambda function:

aws lambda update-function-code --region [Region] --function-name [my-lambda-function] \
  --image-uri=[AWS Account Number].dkr.ecr.[Region].amazonaws.com/[my-lambda-function]:latest

Note: There’s no need to update API Gateway after updating the Lambda function.

Troubleshooting

• Note that your Lambda function and API Gateway will have separate Log Groups in CloudWatch.
• If you get API Gateway "Internal server error", "malformed Lambda proxy response" errors or 502 status codes, it means your Lambda function’s response is not formatted correctly for API Gateway.