Put an API in Front

What you'll learn

A REST API is built from resources (path segments), methods (GET, POST …) and integrations (what answers).
A {number} segment is a path parameter. Lambda receives it in event.pathParameters (in a Python handler, event["pathParameters"]).
CDK creates the deployment, the stage and the permission for API Gateway to invoke the function. You write none of that.

Section 01

A REST API

apigw.RestApi creates the API; deployOptions configures the stage. The default stage is prod; many teams name it after the API version instead, here v1.

Create the API

import * as apigw from "aws-cdk-lib/aws-apigateway";

const api = new apigw.RestApi(this, "PokedexApi", {
  deployOptions: { stageName: "v1" },
});

Section 02

Resources and methods

api.root is the / resource. addResource adds one path segment, and addMethod attaches a verb with an integration. A LambdaIntegration calls the function in proxy mode: API Gateway passes the whole request in, and the function returns the status code and body.

Don't reach for addProxy or an ANY method: that sends every path and verb to one function and gives up per-route throttling, validation and authorization.
The same pokemon resource can hold more methods later (POST for new entries) without repeating the path.

GET /pokemon/{number}

api.root
  .addResource("pokemon")
  .addResource("{number}")
  .addMethod("GET", new apigw.LambdaIntegration(lookupFn));

Section 03

What CDK adds for you

Check the exercise output: besides AWS::ApiGateway::RestApi, Resource and Method, CDK adds a Deployment, a Stage and AWS::Lambda::Permission resources. Without the permission, API Gateway can't invoke the function and callers get a 500 “Internal server error”, a classic hand-written-template bug. The integration makes it for you, one for the test console and one for real traffic.

Practice

Your turn

Expose the lookup function as GET /pokemon/{number}. Create the API with the stage name v1, add a pokemon resource with a {number} child, and attach a Lambda integration to its GET method. Use explicit routes, not a proxy (ANY).

stageName: "v1" and GET /pokemon/{number} routed to lookupFn with a LambdaIntegration.

import * as cdk from "aws-cdk-lib";
import * as dynamodb from "aws-cdk-lib/aws-dynamodb";
import * as lambda from "aws-cdk-lib/aws-lambda";
import * as apigw from "aws-cdk-lib/aws-apigateway";
import { Construct } from "constructs";
export class PokedexStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);
    const table = new dynamodb.Table(this, "PokedexTable", {
      partitionKey: { name: "pokedexNumber", type: dynamodb.AttributeType.NUMBER },
      sortKey: { name: "formId", type: dynamodb.AttributeType.STRING },
      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
    });
    const lookupFn = new lambda.Function(this, "LookupFn", {
      runtime: lambda.Runtime.NODEJS_22_X,
      handler: "index.handler",
      code: lambda.Code.fromAsset("lambda/lookup"),
      timeout: cdk.Duration.seconds(10),
      memorySize: 256,
      environment: { TABLE_NAME: table.tableName },
    });
    // ⬇️ Give the API a "v1" stage and route GET /pokemon/{number} to lookupFn.
    const api = new apigw.RestApi(this, "PokedexApi", {});
  }
}
const app = new cdk.App();
new PokedexStack(app, "PokedexStack");

import * as cdk from "aws-cdk-lib";
import * as dynamodb from "aws-cdk-lib/aws-dynamodb";
import * as lambda from "aws-cdk-lib/aws-lambda";
import * as apigw from "aws-cdk-lib/aws-apigateway";
import { Construct } from "constructs";

export class PokedexStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);
    const table = new dynamodb.Table(this, "PokedexTable", {
      partitionKey: { name: "pokedexNumber", type: dynamodb.AttributeType.NUMBER },
      sortKey: { name: "formId", type: dynamodb.AttributeType.STRING },
      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
    });

    const lookupFn = new lambda.Function(this, "LookupFn", {
      runtime: lambda.Runtime.NODEJS_22_X,
      handler: "index.handler",
      code: lambda.Code.fromAsset("lambda/lookup"),
      timeout: cdk.Duration.seconds(10),
      memorySize: 256,
      environment: { TABLE_NAME: table.tableName },
    });

    // ⬇️ Give the API a "v1" stage and route GET /pokemon/{number} to lookupFn.
    const api = new apigw.RestApi(this, "PokedexApi", {});
  }
}

const app = new cdk.App();
new PokedexStack(app, "PokedexStack");

Ctrl/⌘ Enter to run · simulated, no AWS callsSimulated — no AWS calls

The simulator runs the constructs this course teaches, plus simple loops and helper methods. Other CDK code may not be recognised.

Check

Check your understanding

Quick Quiz · one question, as many tries as you need.

You want GET /pokemon/252 to reach the lookup function. Which construct chain is right?

Choose one answer.