Swift AWS Lambda Template

An opinionated template for deploying serverless functions to AWS Lambda using Swift AWS Lambda Runtime.

Goals:

• streamline deployment
• promote best practices
• improve performance

Features

• build and deploy with single make deploy
• provision all resources using AWS Cloud​Formation (with help from AWS SAM CLI)
• tracing using AWS X-Ray SDK for Swift TODO: restore
• CI workflows using GitHub Actions
• code formatting using swiftformat
• generate documentation using swift-doc

Requirements

• Swift compiler and Package Manager - both included in XCode
• Docker
• Amazon Web Services (AWS) Account
• AWS Serverless Application Model (SAM) CLI
• GNU Make
• swiftformat

Overview

The template contains code with two AWS Lambda functions:

• HelloWorldAPI handling Amazon API Gateway events

as well as a AWS SAM template used to deploy them using AWS SAM CLI.

Since SAM CLI does not support Swift, a Docker image is created and used to cross compile and package Swift code to run in AWS Lambda environment.

Configuration

• Package.swift - Swift Package Manager manifest file defining the package’s name, its contents and dependencies

• template.yaml - AWS SAM Template defining the application's AWS resources

• samconfig.toml - AWS SAM CLI project-level configuration file

• Swift AWS Lambda Runtime Configuration can be fine tuned using environment variables

Deploying to AWS Lambda

Build and deploy:

$ make deploy

This will:

• build Docker image used to cross compile the code (if it does not exist)
• cross compile and package Lambda functions and Swift Linux Runtime Lambda Layer
• prompt to configure AWS SAM project (if samconfig.toml does not exist)
• deploy (create or update) AWS resources defined in template.yaml including Lambda functions and layers

The HelloWorldAPI endpoint is printed after successful deployment, example: https://xxx.execute-api.us-east-1.amazonaws.com/Prod/hello/

Troubleshooting

When prompted, confirm that it is okay to deploy an endpoint without authorization, see:

HelloWorldAPIFunction may not have authorization defined, Is this okay? [y/N]: y

Testing

Unit testing

Build and run tests:

$ swift test

Invoking events (locally)

Set the LOCAL_LAMBDA_SERVER_ENABLED environment variable to true .

HelloWorldAPI

Build and run Lambda:

$ swift run HelloWorldAPI

Invoke the Lambda with curl:

$ curl --header "Content-Type: application/json" \
  --request POST --data @events/api2.json \
  http://localhost:7000/invoke

or with HTTPie:

$ http POST http://localhost:7000/invoke @events/api2.json

Developing

Code Formatting

Format code using swiftformat:

swiftformat .

Consider creating Git pre-commit hook

echo 'swiftformat --lint .' > .git/hooks/pre-commit
chmod +x .git/hooks/pre-commit

GitHub Actions

• Test - Run tests
• Package - Tests creating of packages with lambda functions
• Lint - validates code formatting using swiftformat
• Documentation generates documentation using swift-doc

Note github-wiki-publish-action used by Documentation workflow requires that your repository has the following:

• A wiki with at least one page in it
• A secret named GH_PERSONAL_ACCESS_TOKEN with a Github personal access token with "repo" authorization