README.md

Go functions on AWS Lambda

Uses the following technologies:

• Go programming language
• AWS Lambda to host the function
• 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 ZIP file.

Notes on AWS API Gateway

*NOTE: AWS API Gateway adds a bit of overhead on how you handle parameters (APIGatewayProxyRequest) and response (APIGatewayProxyResponse), which affects how you test it on localhost.

Inspiration and references

Based on AWS Lambda in GoLang — The Ultimate Guide and this example Gist. See also:

• AWS:
  • AWS Go guide
  • Example of AWS Lambda function written in Go
  • AWS API Gateway tutorial: turn Lambda function into REST API

Write your Lambda function in Go

Edit my-lambda-function/main.go

Building both Go binary and ZIP file

make

(Optional: Manual build steps for Go binary and ZIP file)

Build Go binary

Create the working directory

mkdir my-lambda-function && cd my-lambda-function

(Create the files: main.go)

Initialize the module in Go

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

Build the go app for Linux

GOOS=linux go build

Build ZIP file

To build your ZIP file:

cd my-lambda-function && zip -r ../my-lambda-function.zip * && cd ..

Running the Lambda function locally

TBD!

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 '{"body":{"name":"Tom"}}'

✅ You should get a response like {"statusCode":200,"headers":{"Content-Type":"application/json"},"multiValueHeaders":null,"body":"{\"message\":\"Hello! Dear Tom!\"}"}

Note the more complex JSON parameters/response used vs in the final results below, see Notes on AWS API Gateway above.

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

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

Build your local ZIP file:

make

Create a new Lambda function

aws lambda create-function --function-name [my-lambda-function] \
  --handler [my-lambda-function] \
  --zip-file fileb://tmp/[my-lambda-function].zip \
  --runtime go1.x \
  --region [Region] \
  --role arn:aws:iam::[AWS Account Number]:role/lambda-execute

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

aws lambda invoke --function-name [my-lambda-function] \
  --cli-binary-format raw-in-base64-out \
  --payload '{"body":"{\"name\":\"Tom\"}"}' \
  --invocation-type "RequestResponse" tmp/lambda_response.txt

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

Update the Lambda function:

aws lambda update-function-code --region [Region] --function-name [my-lambda-function] \
  --zip-file fileb://tmp/[my-lambda-function].zip

Note: There’s no need to update API Gateway after updating the Lambda function, but it can take a minute or so before the updated Lambda function starts working.

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.