Amazon Lambda Golang Library

AWS CDK v1 has reached End-of-Support on 2023-06-01. This package is no longer being updated, and users should migrate to AWS CDK v2.

For more information on how to migrate, see the Migrating to AWS CDK v2 guide.

This library provides constructs for Golang Lambda functions.

To use this module you will either need to have Go installed (go1.11 or later) or Docker installed. See Local Bundling/Docker Bundling for more information.

This module also requires that your Golang application is using a Go version >= 1.11 and is using Go modules.

Go Function

Define a GoFunction:

lambda_.GoFunction(self, "handler",
    entry="app/cmd/api"
)

By default, if entry points to a directory, then the construct will assume there is a Go entry file (i.e. main.go). Let's look at an example Go project:

lamda-app
├── cmd
│   └── api
│       └── main.go
├── go.mod
├── go.sum
├── pkg
│   ├── auth
│   │   └── auth.go
│   └── middleware
│       └── middleware.go
└── vendor
    ├── github.com
    │   └── aws
    │       └── aws-lambda-go
    └── modules.txt

With the above layout I could either provide the entry as lambda-app/cmd/api or lambda-app/cmd/api/main.go, either will work. When the construct builds the golang binary this will be translated go build ./cmd/api & go build ./cmd/api/main.go respectively. The construct will figure out where it needs to run the go build command from, in this example it would be from the lambda-app directory. It does this by determining the mod file path, which is explained in the next section.

mod file path

The GoFunction tries to automatically determine your project root, that is the root of your golang project. This is usually where the top level go.mod file or vendor folder of your project is located. When bundling in a Docker container, the moduleDir is used as the source (/asset-input) for the volume mounted in the container.

The CDK will walk up parent folders starting from the current working directory until it finds a folder containing a go.mod file.

Alternatively, you can specify the moduleDir prop manually. In this case you need to ensure that this path includes entry and any module/dependencies used by your function. Otherwise bundling will fail.

Runtime

The GoFunction can be used with either the GO_1_X runtime or the provided runtimes (PROVIDED/PROVIDED_AL2). By default it will use the PROVIDED_AL2 runtime. The GO_1_X runtime does not support things like Lambda Extensions, whereas the provided runtimes do. The aws-lambda-go library has built in support for the provided runtime as long as you name the handler bootstrap (which we do by default).

Dependencies

The construct will attempt to figure out how to handle the dependencies for your function. It will do this by determining whether or not you are vendoring your dependencies. It makes this determination by looking to see if there is a vendor folder at the mod file path.

With this information the construct can determine what commands to run. You will generally fall into two scenarios:

1. You are using vendoring (indicated by the presence of a vendor folder) In this case go build will be run with -mod=vendor set
2. You are not using vendoring (indicated by the absence of a vendor folder) If you are not vendoring then go build will be run without -mod=vendor since the default behavior is to download dependencies

All other properties of lambda.Function are supported, see also the AWS Lambda construct library.

Environment

By default the following environment variables are set for you:

• GOOS=linux
• GOARCH: based on the target architecture of the Lambda function
• GO111MODULE=on

Use the environment prop to define additional environment variables when go runs:

lambda_.GoFunction(self, "handler",
    entry="app/cmd/api",
    bundling=lambda.BundlingOptions(
        environment={
            "HELLO": "WORLD"
        }
    )
)

Local Bundling

If Go is installed locally and the version is >= go1.11 then it will be used to bundle your code in your environment. Otherwise, bundling will happen in a Lambda compatible Docker container with the Docker platform based on the target architecture of the Lambda function.

For macOS the recommended approach is to install Go as Docker volume performance is really poor.

Go can be installed by following the installation docs.

Docker

To force bundling in a docker container even if Go is available in your environment, set the forceDockerBundling prop to true. This is useful if you want to make sure that your function is built in a consistent Lambda compatible environment.

Use the buildArgs prop to pass build arguments when building the bundling image:

lambda_.GoFunction(self, "handler",
    entry="app/cmd/api",
    bundling=lambda.BundlingOptions(
        build_args={
            "HTTPS_PROXY": "https://127.0.0.1:3001"
        }
    )
)

Use the bundling.dockerImage prop to use a custom bundling image:

lambda_.GoFunction(self, "handler",
    entry="app/cmd/api",
    bundling=lambda.BundlingOptions(
        docker_image=DockerImage.from_build("/path/to/Dockerfile")
    )
)

Use the bundling.goBuildFlags prop to pass additional build flags to go build:

lambda_.GoFunction(self, "handler",
    entry="app/cmd/api",
    bundling=lambda.BundlingOptions(
        go_build_flags=["-ldflags \"-s -w\""]
    )
)

By default this construct doesn't use any Go module proxies. This is contrary to a standard Go installation, which would use the Google proxy by default. To recreate that behavior, do the following:

lambda_.GoFunction(self, "GoFunction",
    entry="app/cmd/api",
    bundling=lambda.BundlingOptions(
        go_proxies=[lambda_.GoFunction.GOOGLE_GOPROXY, "direct"]
    )
)

Command hooks

It is possible to run additional commands by specifying the commandHooks prop:

// This example only available in TypeScript
// Run additional commands on a GoFunction via `commandHooks` property
new lambda.GoFunction(this, 'handler', {
  bundling: {
    commandHooks: {
      // run tests
      beforeBundling(inputDir: string): string[] {
        return ['go test ./cmd/api -v'];
      },
      // ...
    },
  },
});

The following hooks are available:

• beforeBundling: runs before all bundling commands
• afterBundling: runs after all bundling commands

They all receive the directory containing the go.mod file (inputDir) and the directory where the bundled asset will be output (outputDir). They must return an array of commands to run. Commands are chained with &&.

The commands will run in the environment in which bundling occurs: inside the container for Docker bundling or on the host OS for local bundling.

Additional considerations

Depending on how you structure your Golang application, you may want to change the assetHashType parameter. By default this parameter is set to AssetHashType.OUTPUT which means that the CDK will calculate the asset hash (and determine whether or not your code has changed) based on the Golang executable that is created.

If you specify AssetHashType.SOURCE, the CDK will calculate the asset hash by looking at the folder that contains your go.mod file. If you are deploying a single Lambda function, or you want to redeploy all of your functions if anything changes, then AssetHashType.SOURCE will probaby work.

For example, if my app looked like this:

lamda-app
├── cmd
│   └── api
│       └── main.go
├── go.mod
├── go.sum
└── pkg
    └── auth
        └── auth.go

With this structure I would provide the entry as cmd/api which means that the CDK will determine that the protect root is lambda-app (it contains the go.mod file). Since I only have a single Lambda function, and any update to files within the lambda-app directory should trigger a new deploy, I could specify AssetHashType.SOURCE.

On the other hand, if I had a project that deployed mmultiple Lambda functions, for example:

lamda-app
├── cmd
│   ├── api
│   │   └── main.go
│   └── anotherApi
│       └── main.go
├── go.mod
├── go.sum
└── pkg
    ├── auth
    │   └── auth.go
    └── middleware
        └── middleware.go

Then I would most likely want AssetHashType.OUTPUT. With OUTPUT the CDK will only recognize changes if the Golang executable has changed, and Go only includes dependencies that are used in the executable. So in this case if cmd/api used the auth & middleware packages, but cmd/anotherApi did not, then an update to auth or middleware would only trigger an update to the cmd/api Lambda Function.