Working with the AWS CDK in Go - AWS Cloud Development Kit (CDK)

Working with the AWS CDK in Go

The Go language binding for the AWS CDK is now available as a Developer Preview. It is not suitable for production use and may undergo significant changes before being designated stable. To follow development, see the Project Board on GitHub. Please report any issues you encounter.

Unlike the other languages the CDK supports, Go is not a traditional object-oriented programming language. Go uses composition where other languages often leverage inheritance. We have tried to employ idiomatic Go approaches as much as possible, but there are places where the CDK charts its own path.

This topic explains the ins and outs of working with the AWS CDK in Go. See the announcement blog post for a walkthrough of a simple Go project for the AWS CDK.

Prerequisites

To work with the AWS CDK, you must have an AWS account and credentials and have installed Node.js and the AWS CDK Toolkit. See AWS CDK Prerequisites.

The Go bindings for the AWS CDK use the standard Go toolchain, v1.16 or later. You can use the editor of your choice.

Creating a project

You create a new AWS CDK project by invoking cdk init in an empty directory.

mkdir my-project cd my-project cdk init app --language go

cdk init uses the name of the project folder to name various elements of the project, including classes, subfolders, and files.

The resulting project includes a reference to the AWS CDK Go module, github.com/aws/aws-cdk-go/awscdk, in go.mod. The CDK and its dependencies are automatically installed when you build your app.

Managing AWS Construct Library modules

In most AWS CDK documentation and examples, the word "module" is used primarily to refer to AWS Construct Library modules, one or more per AWS service, which differs from idiomatic Go usage of the term. The CDK Construct Library is provided in one Go module with the individual Construct Library modules, which support the various AWS services, provided as Go packages within that module.

Some services' AWS Construct Library support is in more than one Construct Library module (Go package). For example, Amazon Route 53 has three Construct Library modules in addition to the main awsroute53 package, named awsroute53patterns, awsroute53resolver, and awsroute53targets.

The AWS CDK's core package, which you'll need in most AWS CDK apps, is imported in Go code as github.com/aws/aws-cdk-go/awscdk. Packages for the various services in the AWS Construct Library live under github.com/aws/aws-cdk-go/awscdk. For example, the Amazon S3 module's namespace is github.com/aws/aws-cdk-go/awscdk/awss3.

import ( "github.com/aws/aws-cdk-go/awscdk/awss3" // ... )

Once you have imported the Construct Library modules (Go packages) for the services you want to use in your app, you access constructs in that module using, for example, awss3.Bucket.

AWS CDK idioms in Go

Field and method names

Field and method names use camel casing (likeThis) in TypeScript, the CDK's language of origin. In Go, these follow Go conventions, so are Pascal-cased (LikeThis).

Missing values and pointer conversion

In Go, missing values in AWS CDK objects such as property bundles are represented by nil. Go doesn't have nullable types; the only type that can contain nil is a pointer. To allow values to be optional, then, all CDK properties, arguments, and return values are pointers, even for primitive types. This applies to required values as well as optional ones, so if a required value later becomes optional, no breaking change in type is needed.

When passing literal values or expressions, you can use the following helper functions to create pointers to the values.

  • jsii.String

  • jsii.Number

  • jsii.Bool

  • jsii.Time

For consistency, we recommend that you use pointers similarly when defining your own constructs, even though it may seem more convenient to, for example, receive your construct's id as a string rather than a pointer to a string.

When dealing with optional AWS CDK values, including primitive values as well as complex types, you should explicitly test pointers to make sure they are not nil before doing anything with it. Go does not have "syntactic sugar" to help handle empty or missing values as some other languages do. However, required values in property bundles and similar structures are guaranteed to exist (construction fails otherwise), so these values need not be nil-checked.

Constructs and Props

Constructs, which represent one or more AWS resources and their associated attributes, are represented in Go as interfaces. For example, awss3.Bucket is an interface. Every construct has a factory function, such as awss3.NewBucket, to return a struct that implements the corresponding interface.

All factory functions take three arguments: the scope in which the construct is being defined (its parent in the construct tree), an id, and props, a bundle of key/value pairs that the construct uses to configure the resources it creates. The "bundle of attributes" pattern is also used elsewhere in the AWS CDK.

In Go, props are represented by a specific struct type for each construct. For example, an awss3.Bucket takes a props argument of type awss3.BucketProps. Use a struct literal to write props arguments.

var bucket = awss3.NewBucket(stack, jsii.String("MyBucket"), &awss3.BucketProps{ Versioned: jsii.Bool(true), })

Generic structures

In some places, the AWS CDK uses JavaScript arrays or untyped objects as input to a method. (See, for example, AWS CodeBuild's BuildSpec.fromObject() method.) In Go, these objects are represented as slices and an empty interface, respectively.

The CDK provides variadic helper functions such as jsii.Strings for building slices containing primitive types.

jsii.Strings("One", "Two", "Three")

Developing custom constructs

In Go, it is usually more straightforward to write a new construct than to extend an existing one. First, define a new struct type, anonymously embedding one or more existing types if extension-like semantics are desired. Write methods for any new functionality you're adding and the fields necessary to hold the data they need. Define a props interface if your construct needs one. Finally, write a factory function NewMyConstruct() to return an instance of your construct.

If you are simply changing some default values on an existing construct or adding a simple behavior at instantiation, you don't need all that plumbing. Instead, write a factory function that calls the factory function of the construct you're "extending." In other CDK languages, for example, you might create a TypedBucket construct that enforces the type of objects in an Amazon S3 bucket by overriding the s3.Bucket type and, in your new type's initializer, adding a bucket policy that allows only specified filename extensions to be added to the bucket. In Go, it is easier to simply write a NewTypedBucket that returns an s3.Bucket (instantiated using s3.NewBucket) to which you have added an appropriate bucket policy. No new construct type is necessary because the functionality is already available in the standard bucket construct; the new "construct" just provides a simpler way to configure it.

Building, synthesizing, and deploying

The AWS CDK automatically compiles your app before running it. However, it can be useful to build your app manually to check for errors and to run tests. You can do this by issuing go build at a command prompt while in your project's root directory.

Run any tests you've written by running go test at a command prompt.

The stacks defined in your AWS CDK app can be deployed individually or together using the commands below. Generally, you should be in your project's main directory when you issue them.

  • cdk synth: Synthesizes a AWS CloudFormation template from one or more of the stacks in your AWS CDK app.

  • cdk deploy: Deploys the resources defined by one or more of the stacks in your AWS CDK app to AWS.

You can specify the names of multiple stacks to be synthesized or deployed in a single command. If your app defines only one stack, you do not need to specify it.

cdk synth # app defines single stack cdk deploy Happy Grumpy # app defines two or more stacks; two are deployed

You may also use the wildcards * (any number of characters) and ? (any single character) to identify stacks by pattern. When using wildcards, enclose the pattern in quotes. Otherwise, the shell may try to expand it to the names of files in the current directory before they are passed to the AWS CDK Toolkit.

cdk synth "Stack?" # Stack1, StackA, etc. cdk deploy "*Stack" # PipeStack, LambdaStack, etc.
Tip

You don't need to explicitly synthesize stacks before deploying them; cdk deploy performs this step for you to make sure your latest code gets deployed.

For full documentation of the cdk command, see AWS CDK Toolkit (cdk command).