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How to use aws cdk to create API for your application

In this age of cloud development and serverless architecture, the ability to write infrastructure as code is really powerful.

There are many options to choose from. Let’s explore them!

Options to consider

AWS has several tools to support infrastructure as code. Among them, Cloudformation is the most powerful one but it’s very verbose.

Another option is AWS SAM which is an extension of Cloudformation with reduced syntax. But unlike Cloudformation we have to use JSON or YAML syntax for this.

Then comes the AWS CDK

What is AWS CDK?

According to AWS documentation.

The AWS Cloud Development Kit (AWS CDK) is an open source software development framework to define your cloud application resources using familiar programming languages

In simple terms, we can use our typescript or python code to define resources in the cloud.

This is powerful for us developers because we don’t have to use some fancy YAML syntax to write infrastructure code anymore!

What we will build today?

To understand the power of AWS CDK we will build a simple hello world application. it will have a Lambda function and an ApiGateway resource.

We will invoke the API to get a response from the lambda.

Let’s begin.

Initialize the project

Go to your terminal and run the following commands

mkdir learn-aws-cdk
cd learn-aws-cdk
cdk init app --language typescript

Then install required dependencies

We will need lambda and apigateway to build our application. To install the required dependencies

npm i @aws-cdk/aws-lambda @aws-cdk/aws-apigateway

Well, we will install a special package as well. This package is specially built for nodejs lambdas.

The benefit of using this library is

• This library automatically handles our typescript files (No need for webpack)
• This library enables us to compress the function output.

Let’s add that

npm i @aws-cdk/aws-lambda-nodejs

Now we are ready to write some functions

Create the lambda

Now create a new folder src/hello-lambda . Just to keep things organized

Then create a new file under that folder app.ts

Add the following code

exports.handler = async function (event: any, context: any) {
  console.log("request ", JSON.stringify(event));

  const responseText = "Hello from lambda";

  return {
    headers: {
      "Access-Control-Allow-Origin": "*",
      "Access-Control-Allow-Credentials": true,
      "Access-Control-Allow-Methods": "*",
      "Access-Control-Allow-Headers":
        "Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers, Authorization",
    },

    isBase64Encoded: false,
    multiValueHeaders: {},
    statusCode: 200,
    body: JSON.stringify(responseText),
  };
};

Now we have the lambda but where do we use it?

Add the lambda to our stack

Now head over to the lib/learn-aws-cdk-stack.ts

Add the following codes to include your lambda and apigateway to the stack

import * as cdk from "@aws-cdk/core";
import * as lambda from "@aws-cdk/aws-lambda";
import * as apigateway from "@aws-cdk/aws-apigateway";
import { NodejsFunction, NodejsFunctionProps } from "@aws-cdk/aws-lambda-nodejs";

import * as path from "path";

export class WinterWonderlandBackendStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // The code that defines your stack goes here

    const myLambda = new NodejsFunction(this, "AttractionsLambdaHandler", {
      runtime: lambda.Runtime.NODEJS_14_X,
      entry: path.join(__dirname, `../src/hello-lambda/app.ts`),
      handler: "handler",
      timeout: cdk.Duration.seconds(20),
      bundling: {
        minify: true,
        externalModules: ["aws-sdk"],
      },
    });

    const api = new apigateway.RestApi(this, "first-api", {
      defaultCorsPreflightOptions: {
        allowOrigins: apigateway.Cors.ALL_ORIGINS,
      },
    });
    const getAllIntegration = new apigateway.LambdaIntegration(myLambda);
    const items = api.root.addResource("hello");
    items.addMethod("GET", getAllIntegration);
  }
}

Notice at the end of the file we have added the cors configuration to be

allowOrigins: apigateway.Cors._ALL_ORIGINS,

This is a nice feature that allows us to allow any URL to hit our API. (Otherwise, you will get a CORS error from the browser if you are trying to hit from a front-end application)

Deploy the stack

Now comes the fun part. First, we need to compile our lambda code which will be handled by the aws-lambda-nodejs library.

Then, we need to generate the cloud formation template for our project. To do all this we just need to run the following command

cdk synth

This will give you a .yaml file as an output on the terminal.

Now if you want to deploy it run the next command. to prepare the environment. First, open the bin/learn-aws-cdk.ts file and uncomment the file that says

env: { account: "YOUR_ACCOUNT_ID", region: "us-east-1" },

Where do you get your account id? Log in to your aws console and click on the top menu over your name.

Now we need to prepare the application as well. To do that run the following command

cdk bootstrap cdk bootstrap aws://YOUR_ACCOUNT_ID/us-east-1

If that is successful now you can run the deploy command to deploy the application to the cloud.

cdk deploy

And you will be greeted with an URL that you can use to call the lambda API.

That’s it for today. Hope you learned something new!

Have a great day! :D

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