Selenium Grid 4 Setup with Docker — Complete Guide (2026)

Last updated 2026-07-20 · 11 min read · By Avinash Kamble, reviewed by Priyanka G.

Selenium Grid 4 is a full rewrite — new event bus, session queue, and Kubernetes-native scaling. If you last set up a grid on 3.x, everything you know about JSON wire protocol and static node registration is gone. This guide gets you to a green Chrome + Firefox grid in 10 minutes and shows the autoscale pattern we use in production.

Key takeaways

• The 3 grid topologies (Standalone, Hub-Node, Fully Distributed).
• A copy-paste docker-compose.yml for hub + Chrome + Firefox.
• Session queue tuning that eliminates the "no free slots" flakes.
• Kubernetes autoscaling via KEDA + the Selenium chart.

services:
  selenium-hub:
    image: selenium/hub:4.24
    ports: ["4442:4442", "4443:4443", "4444:4444"]
  chrome:
    image: selenium/node-chrome:4.24
    shm_size: 2gb
    depends_on: [selenium-hub]
    environment:
      SE_EVENT_BUS_HOST: selenium-hub
      SE_EVENT_BUS_PUBLISH_PORT: 4442
      SE_EVENT_BUS_SUBSCRIBE_PORT: 4443
      SE_NODE_MAX_SESSIONS: 4
  firefox:
    image: selenium/node-firefox:4.24
    shm_size: 2gb
    depends_on: [selenium-hub]
    environment:
      SE_EVENT_BUS_HOST: selenium-hub
      SE_EVENT_BUS_PUBLISH_PORT: 4442
      SE_EVENT_BUS_SUBSCRIBE_PORT: 4443

Point your tests at http://localhost:4444/wd/hub. Grid UI: http://localhost:4444/ui.

Set SE_SESSION_REQUEST_TIMEOUT=300 and SE_SESSION_RETRY_INTERVAL=5 to eliminate the "no free slots" flakes when CI bursts. Also raise SE_NODE_MAX_SESSIONS to (cpu_count × 1.5) — most teams under-provision here.

Use the official Selenium Helm chart with KEDA. It scales browser pods against the session queue length, so idle costs stay low. See the Selenium locators cheat sheet for the test-side complement, and explicit / implicit / fluent waits if you are seeing timeout errors under load.