Automate creation of AWS Stack

Tags: aws cdk cloudformation typescript tutorial

AWS CDK is a great framework to programmatically deploy cloudformation stack. If you are unfamiliar with AWS CDK, I would recommend first to check out Getting started with AWS CDK.

One of the pet peeves I have while designing cloudformation template is redundancy. I have to manually copy-paste the same properties across multiple resources. I wanted to leverage AWS CDK to create an interface that would allow tto dynamically create cloudformation. For the interface, I harked back to the good old CSV file.

For a simple example, let’s consider a simple cloudformation template

Parameters:
  Environment:
    Type: String
    Default: dev
    AllowedValues:
      - dev
      - qa
      - prod
    Description: Enter your environment
  Project:
    Type: String
    Default: version
    Description: Enter your version

What if we have to maintain 100 parameters, resources, etc in our project. Soon it will become tedious to maintain multiple resources. Instead, we create a class called Parameter that we instantiate multiple times using different parameters. Here is a class diagram for our Parameter class.

Using typescript, we can define the class as

	export class Parameter extends cdk.Construct {
	private name : string;
	private default_value: string;
	private desc : string;
	private allowed_values: string;
	constructor(scope: cdk.Construct,
	name: string,
	default_value: string,
	desc: string,
	allowed_values: string) {
	super(scope, parameter_name);
	this.name = name;
	this.default_value = default_value;
	this.desc = desc;
	this.allowed_values = allowed_values;
	}
	create() : void {
	let param : cdk.CfnParameter;
	if (this.allowed_values && this.allowed_values.trim()) {
	param = new cdk.CfnParameter(this, this.name , {
	type: "String",
	default: this.default_value,
	allowedValues: this.allowed_values.split("|").map(function (value : string){ return value.trim()}),
	desc : this.desc
	});
	} else {
	param = new cdk.CfnParameter(this, this.name , {
	type: "String",
	default: this.default_value,
	description : this.desc
	});
	}
	param.overrideLogicalId(this.name);
	}
	}

view raw projectCdk4.ts hosted with ❤ by GitHub

We will create a `CSV` file under folder `resources` which would contain information for each instance of our class.

resource	create	category	default	description	allowed_values
Environment	yes	parameter	dev	Enter your environment	dev | qa | prod
Project	yes	parameter	version1	Enter version

First, we will read our CSV file into our project. We would need to install an additional library to read the file.

$ npm i --save csvtojson

We will edit the lib/project_cdk-stack.ts file.

	import * as cdk from '@aws-cdk/core';
	import * as lib from './helpers';
	export class ProjectCdkStack extends cdk.Stack {
	constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
	super(scope, id, props);
	const filename = "resources/cdkinput.csv";
	lib.read_file(filename).then(result => {
	if (result && result.length) {
	lib.generateTemplate(result, this);
	} else {
	console.log("Input csv is empty. Exiting...");
	}
	}).catch(error => console.log(error));
	}
	}

view raw projectCdk1.ts hosted with ❤ by GitHub

Then we will create lib/helpers.ts file.

	import { ProjectCdkStack } from './project_cdk-stack';
	const csvread = require('csvtojson');
	export async function read_file(filename : string) {
	const jsonArray: any = await csvread().fromFile(filename);
	return jsonArray;
	}
	export function generateTemplate(result : any, obj : ProjectCdkStack){
	//TODO implement
	}

view raw projectCdk2.ts hosted with ❤ by GitHub

Our code till now will not generate any cloudformation. However, we can test it for any compile errors

$ cdk synth --quiet

Next, we will implement our generateTemplate function.

	import { ProjectCdkStack } from './project_cdk-stack';
	const csvread = require('csvtojson');
	import * as cdk from '@aws-cdk/core';
	export function generateTemplate(result : any, obj : ProjectCdkStack){
	result.forEach((item:any) => {
	if (item["create"] === "yes"){
	let object : any;
	switch(item["category"]){
	case 'parameter':
	object = new Parameter(obj,
	item["resource"],
	item["default"],
	item["description"],
	item["allowed_values"]);
	break;
	default:
	break;
	}
	if (object) {
	object.create();
	}
	}
	});
	}

view raw projectCdk3.ts hosted with ❤ by GitHub

Lastly, we can deploy our cloudformation stack using

$ cdk deploy

In the next article, we will update our code to add additional classes to handle resources, output, etc for our cloudformation template.

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