Building a websocket echo server in 33 lines of code

The code below shows how to build a simple websocket echo server with AWS Lambda and API Gateway, with all the infrastructure management handled by Pulumi. A GitHub repository with the full code is available here.

import * as pulumi from "@pulumi/pulumi";
import * as aws from "@pulumi/aws";

const echoHandler = new aws.lambda.CallbackFunction("echoHandler", {
  callback: async (event: any) => ({ statusCode: 200, body: event.body })
});

const api = new aws.apigatewayv2.Api("api", { protocolType: "WEBSOCKET" });

const integration = new aws.apigatewayv2.Integration("defaultIntegration", {
  apiId: api.id,
  integrationType: "AWS_PROXY",
  integrationUri: echoHandler.invokeArn,
});

const defaultRoute = new aws.apigatewayv2.Route("defaultRoute", {
  apiId: api.id,
  routeKey: "$default",
  target: pulumi.interpolate`integrations/${integration.id}`,
});

const deployment = new aws.apigatewayv2.Deployment(
  "deployment",
  { apiId: api.id },
  { dependsOn: [defaultRoute]}
);

const stage = new aws.apigatewayv2.Stage("stage", {
  apiId: api.id,
  name: "dev",
  deploymentId: deployment.id,
});

export const url = pulumi.interpolate`${api.apiEndpoint}/${stage.name}`;

1. echoHandler defines a Lambda function that returns the body of the request (the echo).
2. api creates a new API Gateway configured for websockets.
3. integration associates the Lambda function with the API Gateway. It also configures the integration type to be AWS_PROXY, which means that the Lambda function will receive the entire request object.
4. defaultRoute handles incoming requests that don’t match any other route. In this case, it matches all requests.
5. deployment creates a new deployment of the API Gateway. This is required before we can create a stage.
6. stage represents a state of the API Gateway. In this case, it’s just the dev stage but we could create multiple stages for different environments (e.g. prod).
7. Finally, url is the URL of the API gateway combined with the stage name. This is the URL that clients can connect to.