selenium grid node not registered: how to fix

TL;DR

The node is almost always failing to reach the hub, not failing to start. Check the hub URL the node was given, then check the event-bus ports between them. A node that starts but never appears in the Grid UI is a connectivity problem nine times out of ten.

Problem

The Selenium Grid 4 hub is up and the node process starts, but the node never shows as registered.

Steps

1. Open the Grid UI status page and confirm the hub itself is healthy. Expected: the hub console loads and shows zero nodes.
2. Check the exact hub URL passed to the node, for example YOUR_HOST. Expected: the URL is reachable from the node machine via curl.
3. Verify the event-bus ports 4442 and 4443, plus node port 5557, are open between hub and node. Expected: connections succeed on all three.
4. Match Selenium versions on hub and node; mixed 4.x minors can refuse to pair. Expected: the selenium-server version output matches on both sides.
5. Restart the node with fine-grained logging and read the registration lines. Expected: logs show a successful publish to the hub or the exact refused address.

When to use

• A Selenium Grid 4 node starts but never appears in the hub console.
• Scaling out to new node machines or containers.
• After upgrading the Selenium server jar on one side only.

When not to use

• Sessions fail but nodes show as registered; that is a session-queue or capability-matching issue.
• You run standalone mode; there is no hub to register with.
• The hub itself will not start; fix the hub first.

Tool compatibility

• Selenium 4.x Grid: hub and node roles via the selenium-server jar.
• Event-bus ports 4442 and 4443, node port 5557 by default.

Variant phrasings

selenium grid node not connecting to hub

Same diagnosis path; URL and ports first, versions second.

grid shows 0 nodes registered

Confirm you are looking at the right hub; duplicate hubs on a network are a classic mix-up.

Why it happens

Grid 4 registration is the node publishing itself to the hub over the event bus. Anything that breaks that path, a wrong hub address, blocked ports, or a version mismatch, leaves a running node invisible to the hub.

Edge cases

• In Docker the node must use the hub's container-network address, not the external host address.
• Reverse proxies in front of the hub need websocket-friendly config for the event bus.
• A node that registers then vanishes is usually being out-of-memory killed; check container memory.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst0YzMWdMA5-_2u8KGPDpHw