WebRTC handshake timeout 408 during JMeter spike test

Voice & Telephony
1
  • Genesys Cloud US1
  • JMeter 5.6
  • Target: 200 concurrent WebRTC sessions

Need some help troubleshooting the WebSocket upgrade failures. The handshake fails with 408 Request Timeout when concurrency exceeds 150 agents. The standard API calls work fine, but the media channel drops immediately. Is there a hidden rate limit on the signaling endpoint?

2

This is typically caused by the signaling layer being overwhelmed before the media negotiation completes. The 408 error indicates the server did not receive a complete HTTP request within the configured timeout window. When JMeter simulates 200 concurrent sessions, it often sends WebSocket upgrade requests faster than the Genesys Cloud edge can process the JWT validation and queue assignment logic.

The standard API calls work because they are stateless REST requests. WebRTC requires a persistent, authenticated WebSocket connection. The bottleneck is likely the Architect flow handling the initial interaction. If the flow contains complex data lookups or external API calls before the Answer action, the handshake will timeout.

To mitigate this, adjust the JMeter test configuration to introduce a small delay between connection attempts. Set the Thread Group’s “Ramp-Up Period” to at least 5 seconds per user. This prevents a thundering herd effect on the signaling endpoint. Additionally, verify that the WebSocket URL in your script includes the correct region-specific endpoint for US1. Using a generic endpoint can cause DNS resolution delays.

Warning: Do not increase the server-side timeout values in Genesys Cloud. This will degrade performance for legitimate users. The fix must be on the client side.

Check the Performance dashboard under “Queue Activity” during the test. Look for a spike in “Abandoned Calls” or “Failed Transfers” at the exact moment the 408 errors occur. If the dashboard shows successful logins but failed media connections, the issue is strictly signaling. If the dashboard shows no activity, the requests are being dropped before reaching the flow.

Consider reducing the concurrent user count in JMeter to 100 and increasing the duration. This provides a more realistic load profile and helps isolate whether the issue is concurrency-based or configuration-based. Ensure the JMeter script handles the WebSocket frames correctly, particularly the ping/pong keep-alive messages. Missing these can cause premature connection drops that mimic timeout errors.

3

This is actually a known issue…

The 408 timeout is rarely a Genesys Cloud infrastructure limit. It is usually a client-side configuration mismatch in how JMeter handles the WebSocket upgrade sequence. The signaling endpoint expects a complete HTTP upgrade request within a strict window. If JMeter sends the initial HTTP request but delays the WebSocket handshake completion, the edge drops it.

Try adjusting the JMeter test plan with these specific changes:

  • Disable WebSocket Keep-Alive Pre-fetching: In the WebSocket Open Sampler, uncheck “Open connection only once per thread”. Force each thread to handle its own lifecycle. This prevents connection pooling from masking individual handshake failures.
  • Increase HTTP Request Timeout: Set the httpclient.timeout property in jmeter.properties to at least 60000ms. The default 30000ms is often too short for the JWT validation and queue assignment logic mentioned above.
  • Add a Random Think Time: Insert a “Constant Timer” with a 500-1000ms delay before the WebSocket Open Sampler. This smooths out the spike. Genesys Cloud edge nodes can handle 200 sessions, but not if they all arrive in the same millisecond.
  • Validate JWT Payload Size: Ensure the JWT being passed in the Authorization header is not oversized. A bloated JWT increases parsing time on the edge. Use a minimal scope for the test.

Here is a quick CLI check to verify your current WebSocket connection limits and status codes from the analytics side:

genesyscloud analytics query \
 --interval "2023-10-27T00:00:00Z/2023-10-27T01:00:00Z" \
 --filter "endpoint.type='websocket' AND status.code='408'" \
 --group-by "endpoint.id"

If the 408s are isolated to specific edge nodes, it might be a regional routing issue. But usually, it is just JMeter being too aggressive. Lower the concurrency to 150, add the think time, and ramp up slowly. The platform handles the load fine; the test tool is the bottleneck.