Overview

Pre-configure pools of reserved browsers for immediate acquisition

Browser pools let you maintain a set of reserved, identical browsers ready for immediate use. Use them to set your preferred browser configuration in advance, allowing you to minimize browser start-up latency and scale your workloads in production.

How browser pools work

Browser pools are a way to pre-configure a fixed set of browsers without being charged for them until they are used (i.e. acquired). All browsers in the pool share the same settings upon instantiation.

1. Declare a pool

   First, declare a pool of browsers with your specified configuration. The pool takes time to fill (see fill rate per minute), so declare your pool outside your browser automation / agent runtime logic.

   Pool declarations should be decoupled from browser runtime logic for the best performance.

2. Acquire a browser

   You can acquire a browser as soon as you’ve created a pool. The request returns immediately if a browser is available, or waits until one becomes available.

   The total number of browsers is fixed to the size specified upon browser pool creation. When you acquire a browser, the pool’s available count is decremented by one. When you release a browser, the pool’s available count is incremented by one.

   Put differently, the pool does not top up when you acquire a browser: browsers are “borrowed” from the pool and must be returned when you’re done with them, either by releasing them or allowing them to timeout.

3. Release a browser

   When you’re done with a browser, release it back to the pool. this step is important; otherwise, the browser will continue to be in an acquired state until it times out.

   Failing to release browsers may result in unexpected latency when acquiring future browsers.

Create a pool of reserved browsers

Create a browser pool with a specified size and configuration. All browsers in the pool share the same settings.

Typescript/Javascript

import Kernel from '@onkernel/sdk';

const kernel = new Kernel();

const pool = await kernel.browserPools.create({
  name: "my-pool",
  size: 10,
  stealth: true,
  headless: false,
  timeout_seconds: 600,
  start_url: "https://example.com",
  viewport: {
    width: 1280,
    height: 800
  }
});

console.log(pool.id);

Pool configuration options

Pools can be pre-configured with options like start url, custom extensions, supported viewports, residential proxies, profiles, and more. See the API reference for more details.

Acquire a browser

Acquire a browser from the pool. The request returns immediately if a browser is available, or waits until one becomes available. The acquire_timeout_seconds parameter controls how long to wait; it defaults to the calculated time it would take to fill the pool at the pool’s configured fill rate.

Typescript/Javascript

const browser = await kernel.browserPools.acquire("my-pool", {
  acquire_timeout_seconds: 30,
});

console.log(browser.session_id);
console.log(browser.cdp_ws_url);

The acquired browser includes all the same properties as a regular browser session, including cdp_ws_url for CDP connections and browser_live_view_url for live viewing.

Timeout behavior

Browsers remain in the pool indefinitely until acquired. Once acquired, the pool’s timeout_seconds applies just like a regular browser timeout—if the browser is idle (no CDP or live view connection) for longer than the timeout, it is destroyed and not returned to the pool. The pool will automatically create a replacement browser at the pool’s configured fill rate.

Release a browser

When you’re done with a browser, release it back to the pool. By default, the browser instance is reused. Set reuse: false to destroy it and create a fresh one.

Typescript/Javascript

await kernel.browserPools.release("my-pool", {
  session_id: browser.session_id,
  reuse: true,
});

Update a pool

Update the pool configuration. By default, all idle browsers are discarded and rebuilt with the new configuration.

Typescript/Javascript

const updatedPool = await kernel.browserPools.update("my-pool", {
  size: 20,
  stealth: true,
});

The size parameter is always required when updating a pool, even if you only want to change other settings.

By default, updating a pool discards all idle browsers and rebuilds them with the new configuration. Set discard_all_idle: false to keep existing idle browsers and only apply the new configuration to newly created browsers.

Flush idle browsers

Destroy all idle browsers in the pool. Acquired browsers are not affected. The pool will automatically refill with the pool’s specified configuration.

Typescript/Javascript

await kernel.browserPools.flush("my-pool");

Get pool details

Retrieve the current status and configuration of a pool.

Typescript/Javascript

const pool = await kernel.browserPools.retrieve("my-pool");

console.log(pool.available_count);
console.log(pool.acquired_count);

List pools

List all browser pools in your organization.

Typescript/Javascript

const pools = await kernel.browserPools.list();

for (const pool of pools) {
  console.log(pool.name, pool.available_count);
}

Delete a pool

Delete a browser pool and all browsers in it. By default, deletion is blocked if browsers are currently acquired. Use force: true to terminate acquired browsers and force deletion.

Typescript/Javascript

// Delete a pool (fails if browsers are acquired)
await kernel.browserPools.delete("my-pool");

// Force delete even if browsers are acquired
await kernel.browserPools.delete("my-pool", { force: true });

Full example

This example assumes you’ve already created a pool named “my-pool”. In practice, you’d create pools once (via the SDK, CLI, or dashboard) and then acquire from them repeatedly.

Typescript/Javascript

import Kernel from '@onkernel/sdk';
import { chromium } from 'playwright';

const kernel = new Kernel();

// Acquire a browser from an existing pool
const kernelBrowser = await kernel.browserPools.acquire("my-pool", {});

try {
  // Connect via CDP
  const browser = await chromium.connectOverCDP(kernelBrowser.cdp_ws_url);
  const context = browser.contexts()[0];
  const page = context.pages()[0];

  await page.goto('https://example.com');
  const title = await page.title();
  console.log(title);
} finally {
  // Release back to pool for reuse
  await kernel.browserPools.release("my-pool", {
    session_id: kernelBrowser.session_id,
  });
}

API reference

For more details on all available endpoints and parameters, see the Browser Pools API reference.

Pool sizing calculator

Use the calculator below to estimate a pool size for your workload. It assumes reuse: false on release, so every acquisition ends in destruction and triggers a refill.

How the calculation works

Two constraints have to be satisfied at the same time, so the recommended size is the larger of the two.

Concurrency floor. With a peak acquisition rate λ (per minute) and an average acquired duration d (minutes), the number of browsers held simultaneously trends toward λ × d. We multiply by a 1.25× safety factor to keep ~10–20% of the pool available during normal load (see the pool sizing guidance in the FAQ).

concurrency_floor = ceil(λ × d × 1.25)

Refill floor. The fill_rate_per_minute is a percentage of pool size and is capped at 25. With reuse: false, browsers are destroyed at the acquisition rate, so the refill rate must keep up:

refill_floor = ceil(100 × λ / fill_rate)

Recommended pool size.

N = max(concurrency_floor, refill_floor)

At the 25% fill ceiling, the two constraints meet at d ≈ 3.2 minutes. Below that, the refill ceiling sets the floor; above it, concurrency does.