Configure an HTTP trigger and use WebSocket to trigger a function

How it works

A WebSocket session in Function Compute follows this flow:

1. The client sends an HTTP upgrade request to the HTTP trigger endpoint.

2. Function Compute performs authentication (if configured) and routes the request to a function instance.

3. The function instance handles the connection and processes messages until the connection closes or the execution timeout is reached.

4. When the timeout is reached, Function Compute forcibly closes the connection and the client receives status code 1006.

Prerequisites

Before you begin, ensure that you have:

• A function using the Node.js 14 runtime. For setup instructions, see Create a function

Step 1: Create a trigger

1. Log on to the Function Compute console. In the left-side navigation pane, click Functions.

2. In the top navigation bar, select a region. On the Functions page, click the function you want to manage.

3. On the function details page, click the Configurations tab. In the left-side navigation pane, click Triggers, then click Create Trigger.

4. In the Create Trigger panel, configure the following parameters and click OK.

After the trigger is created, you can update Version or alias, Request methods, Disable internet URL, and Authentication method at any time.

Step 2: Write and deploy the code

1. On the function details page, click the Code tab. In the WebIDE, open index.js and replace its contents with the following Node.js code.

   The WebSocket server must listen on 0.0.0.0, not 127.0.0.1 or localhost. If you do not set a custom port, port 9000 is used by default.

   const WebSocket = require('ws');
   
   const WebSocketServer = WebSocket.Server;
   
   const wss = new WebSocketServer({
     host: "0.0.0.0",
     port: 9000,
   });
   
   wss.on('connection', function (ws, req) {
     console.log(`[SERVER] connection()`);
     ws.on('message', function (message) {
       ws.send(`${message}`, (err) => {
         if (err) {
           console.log(`[SERVER] error: ${err}`);
         }
       });
     })
   });

   The directory structure in the WebIDE looks like this:

2. In the WebIDE terminal, run the following command to install the ws dependency.

   npm install ws

   After installation, package-lock.json is generated automatically. The updated directory structure looks like this:

3. Click Deploy Code to deploy your function.

Step 3: Test the function

1. On the function details page, click the Triggers tab to view and copy the public endpoint URL.

   

2. Paste the trigger URL into Postman and change the scheme from https to wss. For more information, see Postman.

Billing

WebSocket connections are billed the same way as HTTP requests — as long-lived HTTP calls.

• Concurrency = 1: billing starts when the connection is established and stops when it closes.

• Concurrency > 1: billing starts when the first connection is received by an instance and stops when the last connection on that instance closes. Multiple simultaneous connections on the same instance are billed as one.

Example: A function with concurrency set to 2. The first request arrives at T1 and closes at T3. The second request arrives at T2 and closes at T4. The billable duration is T4−T1. The overlapping period T2–T3 is billed only once.

Usage notes

More examples

The following repositories contain WebSocket examples for custom runtimes and custom containers.

FAQ

What's next

• Configure triggers using the Serverless Devs tool. See Common commands of Serverless Devs.

• Configure triggers using SDKs. See SDKs.

• Modify or delete an existing trigger. See Manage triggers.