Node in Selenium Grid
Node is a remote machine (physical or virtual) that is registered with the Hub and actually executes the browser tests.
Node characteristics:
- ✓Has one or more browsers installed (Chrome, Firefox, Edge, etc.)
- ✓Registers itself with the Hub so the Hub knows what capabilities it offers
- ✓Receives test commands from the Hub and executes them in the browser
- ✓Can run multiple browser instances simultaneously (configurable
maxInstances) - ✓There can be multiple nodes in a Selenium Grid
Registering a Node with the Hub:
Bash
# Selenium 3
java -jar selenium-server-standalone-3.141.59.jar \
-role node \
-hub http://localhost:4444/grid/register \
-browser browserName=chrome,maxInstances=3 \
-browser browserName=firefox,maxInstances=3
# Custom port for node
java -jar selenium-server-standalone-3.141.59.jar \
-role node \
-hub http://hub-machine:4444/grid/register \
-port 5555
Selenium 4 Node:
Bash
java -jar selenium-server-4.x.x.jar node \
--hub http://hub-server:4444 \
--port 5555
Node configuration JSON (Selenium 3):
JSON
{
"capabilities": [
{
"browserName": "chrome",
"maxInstances": 3,
"seleniumProtocol": "WebDriver"
},
{
"browserName": "firefox",
"maxInstances": 3,
"seleniumProtocol": "WebDriver"
}
],
"maxSession": 6,
"port": 5555,
"host": "node-machine-ip",
"hubHost": "hub-machine"
}
Multi-node setup:
CODE
[Hub: hub-server:4444]
├── [Node 1: win-machine:5555] — Chrome x3, Firefox x3
├── [Node 2: mac-machine:5556] — Safari x2, Chrome x2
└── [Node 3: linux-machine:5557] — Firefox x4, Edge x2
Node vs Hub:
| Hub | Node | |
|---|---|---|
| Role | Routes requests | Executes tests |
| Has browser | No | Yes |
| Port | 4444 | 5555 (configurable) |
| Count | 1 per Grid | Many |
| Purpose | Central manager | Test executor |
Key definition: Node is the machine which is attached to the Hub. There can be multiple nodes in Selenium Grid. Each node has browsers installed and runs the actual test sessions.