selenium-grid4-remotewebdriver-spurious-exception

🧪 Introduction

When working with Selenium Grid 4 using RemoteWebDriver, you might encounter unexpected or “spurious” exceptions that seem random or hard to reproduce.

These errors can break test execution on a distributed setup — especially in CI/CD environments. In this post, we’ll walk through:

• What the exception typically looks like
• Root causes of spurious exceptions
• How to debug and resolve the issue

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❗ Common Spurious Exception Example

You may see something like:

org.openqa.selenium.remote.http.ConnectionFailedException: Unable to establish websocket connection to ws://localhost:4444/session/<session_id>

Or:

java.net.SocketException: Connection reset  
	at java.base/sun.nio.ch.SocketChannelImpl.throwConnectionReset

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🛠️ Possible Causes

1. RemoteWebDriver version mismatch
   • Make sure the client bindings match the Selenium Grid server version.
2. Hub/Node communication issues
   • Network latency, firewall, or Docker misconfigurations can interrupt the connection.
3. WebSocket handshake failures
   • Selenium Grid 4 uses WebSocket connections; any SSL/TLS mismatch or proxy may cause silent failures.
4. Session timeout or early termination
   • If a node is under high load, sessions may unexpectedly expire or be terminated.
5. Grid not ready or node startup delay
   • Running RemoteWebDriver before the node registers fully can cause flakiness.

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🧩 How to Fix or Mitigate

✅ 1. Match Client & Grid Versions

Ensure you’re using the same Selenium version across your test script, Grid server, and nodes.

<dependency>
  <groupId>org.seleniumhq.selenium</groupId>
  <artifactId>selenium-java</artifactId>
  <version>4.x.x</version>
</dependency>

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✅ 2. Increase Timeout Settings

If you’re using Java:

HttpClient.Factory factory = new NettyClient.Factory();
RemoteWebDriver driver = new RemoteWebDriver(
    new URL("http://localhost:4444"),
    options,
    factory
);

You can also try adding a longer command timeout if using Docker Grid setup.

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✅ 3. Check Node Logs & Grid UI

Visit:
http://localhost:4444/ui

Check for:

• Node registration status
• Session status
• Errors in logs (hub or node containers)

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✅ 4. Run Grid in Standalone for Debugging

To isolate the issue, try running Grid in standalone mode:

java -jar selenium-server-4.x.x.jar standalone

If it works here but not in distributed mode, the problem is likely in the hub-node networking or Docker config.

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✅ 5. Disable WebSocket (Experimental)

If WebSocket issues persist, try disabling them (not recommended long-term):

SE_NODE_ENABLE_WEBSOCKETS=false

Only as a last resort.

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✅ Conclusion

Spurious exceptions in Selenium Grid 4 using RemoteWebDriver are usually caused by version mismatches, network instability, or WebSocket issues. With correct setup and debugging, these can be avoided and mitigated.

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