Welcome to swift-lambda’s documentation!

swift-lambda brings the power and ease-of-use of the Swift programming language to the scalability and buzzword-compliance of AWS Lambda. Use the tools you already know and love to power the backend of your mobile application.

Check out the Quickstart to get up and running in a few minutes.

Quickstart

swift-lambda brings the power and ease-of-use of the Swift programming language to the scalability and buzzword-compliance of AWS Lambda. Use the tools you already know and love to power the backend of your mobile application.

Installation

swift-lambda can be installed using Homebrew:

$ brew install --HEAD awswift/swift-lambda/swift-lambda

Pre-requisites

• A Swift programming environment. On macOS, this means installing Xcode. On Linux, it means downloading Swift from the official website.

• Docker. We use Docker to emulate a local version of the Linux-y AWS Lambda runtime environment. Because Swift compiles to native code, we need to compile the code on a computer that is as similar to Lambda as possible.

  Note that this is still needed even if you are running on Ubuntu, because Lambda is different enough from Ubuntu that compiling on your own machine won’t work.

• Interim: The AWS CLI. Porting the AWS APIs is still a work in progress in the awswift/Awswift repo. Until that is complete we have relied on shelling out to the CLI tool for the alpha release.

• Interim: The stackup Ruby gem. This is a great utility for dealing with CloudFormation and we are shelling out to it until such functionality has been replicated in a Swift library.

Usage

swift lambda setup

setup is a once-off command that will get an AWS account ready for Swift-powered AWS Lambda functions. Right now it creates an S3 bucket for storing your code and an IAM execution role to grant your Lambda functions permission to write logs.

swift lambda init <name>

init will initialise a brand-new Hello, World! Swift-powered AWS Lambda function. Everything you need to get up and running will be created for you. <name> is how you tell the init command what you want your function to be called!

swift lambda build

build will create the Zip archive that you upload to AWS Lambda in order to run your code. swift-lambda will compile your code in a Lambda-like Docker container, zip it up (alongside the Swift runtime) and stick in a few extra files that Lambda requires you to have.

swift lambda deploy [--new-version] [--skip-libs]

deploy is how you get the Zip file from the previous command onto Lambda itself. You could upload the zip using the AWS web console, but we provide this convenience helper so you can iterate on your code as quickly as you can type.

--skip-libs skips uploading the native libraries that the Swift function depends on. This makes for a much faster deployment process. Note that this flag is temporary and will be automatically calculated and hence removed soon.

~~--new-version lets you take advantage of AWS Lambda function versioning. It will increment your function’s version number with this latest upload.~~

swift lambda logs [--tail]

logs allows you to see everything you print() in your Lambda function from the comfort of your terminal. This can be invaluable while debugging to see what is going on.

--tail will output log lines to your terminal as they happen in real-time.

swift lambda destroy

destroy deletes all artifacts of your Lambda function on AWS. Maybe you’re done with a dev version of your code and ready to start a new project - stop paying for storage and cluttering up your Lambda web console.

swift lambda debug

debug allows you to step through your Lambda function from within Xcode, as if you were running it locally.

swift lambda invoke [--async] [--local]

invoke will execute your Lambda function and return its output to your terminal.

--async can be used for long-running Lambda functions where you don’t want to wait for it to finish. You can still monitor its progress using logs.

--local will run your Lambda function inside a Lambda-like Docker container on your own computer. This might be preferable if you have no Internet connectivity and can’t upload your function to AWS.

Function structure

Beyond the Swift code itself, swift-lambda also needs a swift-lambda.json file to know a bit about your intentions for this code. It is a JSON file that has some of the values required for publishing your code to Lambda. The structure is as follows:

{
    "Name": "Swifty McLambdaface",
    "Description": "My awesome new backend function written in Swift",
    "Memory": 128,
    "Timeout": 30
}

You will also have a Package.swift as per Swift Package Manager conventions. It can be as simple as:

import PackageDescription

let package = Package(
    name: "lambdaface",
    dependencies: [
        .Package(url: "https://github.com/awswift/swift-lambda-runtime", majorVersion: 0, minor: 1)
    ]
)

Finally, the last required piece is Sources/main.swift. This is the entrypoint to the Swift executable that swift-lambda will call. An example file would be:

import Foundation
import SwiftLambdaRuntime

SwiftLambdaRuntime().run { event, context, callback in
    let name = event["name"] ?? "World" 
    callback(["output": "Hello, \(name)"])
}

swift-lambda.json manifest

Projects utilising the swift-lambda project include a swift-lambda.json manifest file in their root directory alongside SwiftPM’s Package.swift. This file is mandatory and includes information that swift-lambda needs in order to successfully deploy your function to AWS Lambda.

Basic

In its basic form, this is a JSON file that looks like the following:

{
    "Name": "Swifty McLambdaface",
    "Description": "My awesome new backend function written in Swift",
    "Memory": 128,
    "Timeout": 30,
    "AptDependencies": [
        "openssl-dev"
    ]
}

• The Name field is how we refer to our function. AWS Lambda lets you define as many functions as you need, so being able to refer to them by name is helpful.
• The Description field is similarly useful for distinguishing between Lambda functions when you have many defined.
• The Memory field is mandatory and should be an integer between 128 and 1536. This is how much memory Lambda will make available to your Swift program while it runs. CPU performance is also allocated to your function proportionate to the amount of memory allocated.
• The Timeout field is a mandatory integer between 1 and 300. This is how many seconds that Lambda will wait before considering your function to have timed out and be forcibly terminated. You are billed per 100ms of actual runtime, not how much time you allocate.
• The AptDependencies field is optional. It is an array of native dependencies that your Swift program (or its packages) needs in order to compile.

Advanced

Eventually your needs may exceed that provided by the basic manifest file format. In this case, you can upgrade to using an AWS CloudFormation template to describe your function and infrastracture-as-code.

CloudFormation allows you to describe database tables, push notification topics, S3 file upload buckets and any other AWS resources you might need in addition to your Lambda function to support your mobile application.

Here is an example of a CloudFormation swift-lambda manifest file:

{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Metadata": {
        "Name": ""
    },
    "Resources": {

    },
}

CloudFormation rationale

Our rationale for exposing raw CloudFormation is that a) you shouldn’t have to learn a new standard when an existing one will do and b) we don’t want to reinvent the wheel.

Required IAM permissions

In order to operate correctly, swift-lambda needs permission to access certain AWS APIs on your behalf. If you’re a solo dev and you’ve set up the AWS CLI using aws configure, you will have unlimited access and running swift-lambda from the terminal should work just fine.

However, if swift-lambda is running on a CI machine or your AWS access has been granted by your company’s AWS gurus, your access may be restricted. In order to operate fully, swift-lambda requires the following permissions. They are described in an AWS IAM Policy document in JSON format below. This policy covers everything you need to run swift-lambda’s setup, deploy, invoke and destroy commands.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Stmt1482554544203",
            "Action": [
                "cloudformation:CreateStack",
                "cloudformation:DeleteStack",
                "cloudformation:DescribeStackEvents",
                "cloudformation:DescribeStacks",
                "cloudformation:ListExports",
                "cloudformation:UpdateStack",
                "iam:AttachRolePolicy",
                "iam:CreateRole",
                "iam:DeleteRole",
                "iam:DeleteRolePolicy",
                "iam:DetachRolePolicy",
                "iam:GetRole",
                "iam:PassRole",
                "iam:PutRolePolicy",
                "lambda:CreateFunction",
                "lambda:DeleteFunction",
                "lambda:GetFunction",
                "lambda:GetFunctionConfiguration",                
                "lambda:InvokeFunction",
                "lambda:UpdateFunctionCode",
                "lambda:UpdateFunctionConfiguration",
                "logs:DescribeLogStreams",
                "logs:GetLogEvents",
                "s3:CreateBucket",
                "s3:DeleteBucket",
                "s3:GetObject",
                "s3:GetObjectVersion",
                "s3:PutBucketVersioning",
                "s3:PutObject"
            ],
            "Effect": "Allow",
            "Resource": "*"
        }
    ]
}

Continuous Integration

swift-lambda uses a self-hosted Jenkins instance its continuous integration system. It is hosted at jenkins.awswift.ge.cx and is publicly accessible.

All pull requests to swift-lambda are built and have unit tests and a series of checks run against them. The results of these tests are posted to GitHub on their respective PR threads, but are also available directly on Jenkins.

The CI process that is run against each commit is defined in the swift-lambda repo itself in the Jenkinsfile in the root of the repo. Here you can also see the battery of checks that each PR is subjected to. Essentially if swiftlint reports any style issues, xcodebuild has any build warnings (or errors!) or swift test is unhappy the Awswift bot will let you know via the PR thread on GitHub.

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