Easy going - programming AWS Resources with the CDK in GO

CDK GO is in preview, here are the pros and cons and a first VPC example

TL;DR The GO module system is IMHO neater than node.JS or Python. But you have to get used to the strongly typed language GO.

Init App

In CDK you generate the app skeleton with a single command. The generation of the GO app is really fast ( under one second):

mkdir go-vpc && cd go-vpc
cdk init app --language=go

Files

Name	Description
cdk.json	the usual cdk configuration
go-vpc.go	this is the single app file
go-vpc_test.go	testing, called with go test
go.mod	this is the go package configuration
README.md	all you need to know

Import constructs for VPC

You change the "sns" import to ec2 in the import section of go-vpc.go (line 5):

  3 import (
  4         "github.com/aws/aws-cdk-go/awscdk"
  5         "github.com/aws/aws-cdk-go/awscdk/awsec2"
  6         "github.com/aws/constructs-go/constructs/v3"
  7         "github.com/aws/jsii-runtime-go"
  8 )

You may download each import with:

go get github.com/aws/aws-cdk-go/awscdk/awsec2

Or you get all imports automatically with

go mod tidy

Or you just let the CDK handle that!

The app configuration in cdk.json is:

"app": "go mod download && go run go-vpc.go",

1) go mod download - this handles all imports
2) go run go-vpc.go - this compiles and runs the app

So, if you just start a cdk diff or cdk ls, all modules will be downloaded.
More information about the GO module system gives: go mod help.

Define VPC

Do I have to mention where?

Just add some code after // The code that defines your stack goes here

awsec2.NewVpc(stack, jsii.String("MyVpc"),
        &awsec2.VpcProps{
                Cidr: jsii.String("10.0.0.0/16"),
        },
)

Call diff

cdk diff

Call deploy

cdk deploy

That was easy :) .

No npm or pip actions, just define import settings and go (pun intended)

Differences to TypeScript

TypeScript is strongly typed

In TS the VPC definition looks like this:

1) Strings

• Most strings are - strings 2) properties
• TS knows that { cidr: "10.0.0.0./16" } is a valid VPC property. But you could add properties that are not valid.
• the property values are just - strings

GO is really strongly typed

In GO the type system much more rigid:

1) String pointer
Just like in the AWS GO SDK with the "aws.String" helper, jsii helps you in converting the "MyVpc" string to a string pointer

The definition of the NewPVC is:

func awsec2.NewVpc(scope constructs.Construct, id *string, props *awsec2.VpcProps) awsec2.Vpc

So id is a "*string", which means an pointer to a string. Usually, you would have to do:

myid := "MyVpc"
...
awsec2.NewVpc(stack, &myid...)

2) You have to define explicitly define that vpc props are VpcProps.
This may seem overly complicated, but it enforces the right properties and makes some IDE help easier to implement.

TypeScript is an addition to JavaScript

And so we have some more files just for the TypeScript Compiler (tsconfig.json) and the external testing system (jest).

GO has all included

With GO you have fewer files:

Fast >> slow >> Virusscan

I was a little bit disappointed that go cdk is not faster, but much slower than typescript. But as it turned out, not GO is to blame, but my Virus Scan module. So i checked the timing on AWS cloudshell (tm). With cloudshell you just have to install go 1.16, because yum still has go 1.15.

Environment	Language	Command	Time
Mac with Sophos Virus	go	cdk diff	20 sec
Mac with some Scan disabled	go	cdk diff	10 sec
Mac with Sophos Virus	ts	cdk diff	7 sec
Mac with some Scan disabled	ts	cdk diff 3 sec
cloudshell	ts	init app	33 s
cloudshell	ts	npm i @aws-cdk/aws-ec2	10 sec
cloudshell	ts	cdk diff	7 sec
cloudshell	go	init app	1 s
cloudshell	go	cdk diff first time	30 s
cloudshell	go	cdk diff second time	7 s

Ready to go

Again the CDK team and contributors around the world have done a tremendous job!

With CDK go the package handling is much more smoother and if you get used to the really strong type system, maybe you should give it a try!

Thanks to

Photo by Balkouras Nicos on Unsplash

This post is also published on the great https://aws-blog.de/

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