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Deploy a Browser Rendering Worker with Durable Objects

Last reviewed: about 1 year ago

By following this guide, you will create a Worker that uses the Browser Rendering API along with Durable Objects to take screenshots from web pages and store them in R2.

Using Durable Objects to persist browser sessions improves performance by eliminating the time that it takes to spin up a new browser session. Since Durable Objects re-uses sessions, it reduces the number of concurrent sessions needed.

  1. Sign up for a Cloudflare account ↗.
  2. Install Node.js ↗.

Node.js version manager

Use a Node version manager like Volta ↗ or nvm ↗ to avoid permission issues and change Node.js versions. Wrangler, discussed later in this guide, requires a Node version of 16.17.0 or later.

1. Create a Worker project

Cloudflare Workers provides a serverless execution environment that allows you to create new applications or augment existing ones without configuring or maintaining infrastructure. Your Worker application is a container to interact with a headless browser to do actions, such as taking screenshots.

Create a new Worker project named browser-worker by running:

Terminal window
npm create cloudflare@latest -- browser-worker

2. Enable Durable Objects in the dashboard

To enable Durable Objects, you will need to purchase the Workers Paid plan:

  1. Log in to the Cloudflare dashboard ↗, and select your account.
  2. Go to Workers & Pages > Plans.
  3. Select Purchase Workers Paid and complete the payment process to enable Durable Objects.

3. Install Puppeteer

In your browser-worker directory, install Cloudflare’s fork of Puppeteer:

Terminal window
npm install @cloudflare/puppeteer --save-dev

4. Create a R2 bucket

Create two R2 buckets, one for production, and one for development.

Note that bucket names must be lowercase and can only contain dashes.

Terminal window
wrangler r2 bucket create screenshots
wrangler r2 bucket create screenshots-test

To check that your buckets were created, run:

Terminal window
wrangler r2 bucket list

After running the list command, you will see all bucket names, including the ones you have just created.

5. Configure wrangler.toml

Configure your browser-worker project’s wrangler.toml file by adding a browser binding and a Node.js compatibility flag. Browser bindings allow for communication between a Worker and a headless browser which allows you to do actions such as taking a screenshot, generating a PDF and more.

Update your wrangler.toml configuration file with the Browser Rendering API binding, the R2 bucket you created and a Durable Object:

name = "rendering-api-demo"
main = "src/index.js"
compatibility_date = "2023-09-04"
compatibility_flags = [ "nodejs_compat"]
account_id = <ACCOUNT_ID>




# Browser Rendering API binding
browser = { binding = "MYBROWSER" }


# Bind an R2 Bucket
[[r2_buckets]]
binding = "BUCKET"
bucket_name = "screenshots"
preview_bucket_name = "screenshots-test"


# Binding to a Durable Object
[[durable_objects.bindings]]
name = "BROWSER"
class_name = "Browser"


[[migrations]]
tag = "v1" # Should be unique for each entry
new_classes = ["Browser"] # Array of new classes

6. Code

The code below uses Durable Object to instantiate a browser using Puppeteer. It then opens a series of web pages with different resolutions, takes a screenshot of each, and uploads it to R2.

The Durable Object keeps a browser session open for 60 seconds after last use. If a browser session is open, any requests will re-use the existing session rather than creating a new one. Update your Worker code by copy and pasting the following:

import puppeteer from "@cloudflare/puppeteer";


export default {
  async fetch(request, env) {
    let id = env.BROWSER.idFromName("browser");
    let obj = env.BROWSER.get(id);


    // Send a request to the Durable Object, then await its response.
    let resp = await obj.fetch(request.url);


    return resp;
  },
};


const KEEP_BROWSER_ALIVE_IN_SECONDS = 60;


export class Browser {
  constructor(state, env) {
    this.state = state;
    this.env = env;
    this.keptAliveInSeconds = 0;
    this.storage = this.state.storage;
  }


  async fetch(request) {
    // screen resolutions to test out
    const width = [1920, 1366, 1536, 360, 414];
    const height = [1080, 768, 864, 640, 896];


    // use the current date and time to create a folder structure for R2
    const nowDate = new Date();
    var coeff = 1000 * 60 * 5;
    var roundedDate = new Date(
      Math.round(nowDate.getTime() / coeff) * coeff,
    ).toString();
    var folder = roundedDate.split(" GMT")[0];


    //if there's a browser session open, re-use it
    if (!this.browser || !this.browser.isConnected()) {
      console.log(`Browser DO: Starting new instance`);
      try {
        this.browser = await puppeteer.launch(this.env.MYBROWSER);
      } catch (e) {
        console.log(
          `Browser DO: Could not start browser instance. Error: ${e}`,
        );
      }
    }


    // Reset keptAlive after each call to the DO
    this.keptAliveInSeconds = 0;


    const page = await this.browser.newPage();


    // take screenshots of each screen size
    for (let i = 0; i < width.length; i++) {
      await page.setViewport({ width: width[i], height: height[i] });
      await page.goto("https://workers.cloudflare.com/");
      const fileName = "screenshot_" + width[i] + "x" + height[i];
      const sc = await page.screenshot({ path: fileName + ".jpg" });


      await this.env.BUCKET.put(folder + "/" + fileName + ".jpg", sc);
    }


    // Close tab when there is no more work to be done on the page
    await page.close();


    // Reset keptAlive after performing tasks to the DO.
    this.keptAliveInSeconds = 0;


    // set the first alarm to keep DO alive
    let currentAlarm = await this.storage.getAlarm();
    if (currentAlarm == null) {
      console.log(`Browser DO: setting alarm`);
      const TEN_SECONDS = 10 * 1000;
      await this.storage.setAlarm(Date.now() + TEN_SECONDS);
    }


    return new Response("success");
  }


  async alarm() {
    this.keptAliveInSeconds += 10;


    // Extend browser DO life
    if (this.keptAliveInSeconds < KEEP_BROWSER_ALIVE_IN_SECONDS) {
      console.log(
        `Browser DO: has been kept alive for ${this.keptAliveInSeconds} seconds. Extending lifespan.`,
      );
      await this.storage.setAlarm(Date.now() + 10 * 1000);
      // You could ensure the ws connection is kept alive by requesting something
      // or just let it close automatically when there  is no work to be done
      // for example, `await this.browser.version()`
    } else {
      console.log(
        `Browser DO: exceeded life of ${KEEP_BROWSER_ALIVE_IN_SECONDS}s.`,
      );
      if (this.browser) {
        console.log(`Closing browser.`);
        await this.browser.close();
      }
    }
  }
}

7. Test

Run npx wrangler dev --remote to test your Worker remotely before deploying to Cloudflare’s global network. Local mode support does not exist for Browser Rendering so --remote is required.

8. Deploy

Run npx wrangler deploy to deploy your Worker to the Cloudflare global network.

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