Architect Flow Timeout 504 During High-Concurrency JMeter Test

Dealing with a very strange bug here with our Architect flow when simulating high-concurrency voice traffic. The flow is pretty simple: Greeting → Collect Input → Transfer. It works fine with 50 concurrent threads. But as soon as we push past 150 concurrent calls in JMeter, the ‘Collect Input’ block starts failing with a 504 Gateway Timeout.

The error happens specifically after the 30-second input timeout. The logs show the WebSocket connection remains open, but the response from the transfer block never returns to the client. We are using Genesys Cloud API v2 endpoints for the initial dial.

We checked the API rate limits, and we are nowhere near the cap. The issue seems to be tied to how the platform handles the state of the conversation when the load spikes. Is there a known limit on concurrent active conversations per Architect flow version?

Our JMeter config uses a ramp-up of 5 seconds per thread. We have tried increasing the timeout in the test plan, but the server-side timeout seems to be the bottleneck. Any insights on capacity limits for complex flows under load?

Check your JMeter HTTP Request Defaults for the “Connection Timeout” and “Response Timeout” settings. The 504 Gateway Timeout you are seeing is likely not a Genesys Cloud platform failure, but rather JMeter giving up on the WebSocket handshake or the subsequent HTTP request before the platform finishes processing the high-volume burst. When pushing past 150 concurrent threads, the local machine’s network stack and the JMeter engine itself can become bottlenecks, especially if the “Collect Input” block relies on a stable WebSocket connection that takes slightly longer to establish under load. In my recent tests with similar concurrent volumes, I found that increasing the JMeter “Connect Timeout” to 60000ms and “Response Timeout” to 120000ms resolved many false-positive 504 errors. Additionally, ensure you are using the HTTP Request sampler with the “Use Keep-Alive” option checked, as re-establishing TCP connections for each of the 150+ threads adds significant latency. If the issue persists, try splitting the load across multiple JMeter instances using a distributed testing setup. A single instance often hits OS-level file descriptor limits or CPU contention when managing hundreds of simultaneous WebSocket streams, which can cause the client-side timeout to trigger even if the GC backend is healthy. You can also add a small randomized delay (50-200ms) in the Timer configuration to smooth out the spike, preventing the initial surge from overwhelming the connection pool. This approach mimics more realistic user behavior and helps identify if the 504 is truly a platform capacity issue or just a client-side configuration limit.

This is a classic case of Architect flow throttling masquerading as a gateway timeout. While the suggestion above correctly points to JMeter configuration, it is worth noting that Genesys Cloud has stricter concurrency limits on specific flow nodes compared to Zendesk’s more forgiving webhook infrastructure. When migrating high-volume voice campaigns, the platform enforces a hard limit on simultaneous active sessions within a single flow branch. If that limit is breached, the platform does not reject the connection immediately but instead queues requests until the input timeout expires, resulting in the 504 error you are seeing.

To resolve this, adjust the Collect Input block settings in Architect to reduce the timeout value from 30 seconds to a lower threshold, such as 10-15 seconds, for test scenarios. This forces faster state transitions and prevents resource accumulation. Additionally, ensure your Routing Strategy is set to Longest Available Agent rather than Equal Distribution during load tests, as the latter can cause uneven load spikes on specific edge nodes. In Zendesk, we relied on the platform’s automatic queuing, but Genesys Cloud requires explicit Flow Control configurations. You can also add a Delay node before the Collect Input block with a randomized wait time (e.g., 500ms-2s) to stagger incoming requests and simulate more realistic human interaction patterns, which often bypasses the artificial burst limits triggered by JMeter.

Have you tried adjusting the SIP registration keep-alive intervals and reviewing the carrier-specific failover logic? The 504 Gateway Timeout often stems from upstream carrier timeouts rather than internal Architect flow limits, especially when BYOC trunks are involved.

• Verify that your SIP credentials and outbound routing rules in Genesys Cloud are aligned with the carrier’s expected session duration. Some carriers drop idle connections after 30 seconds if no DTMF is detected.
• Check if the WebSocket connection is properly handling retransmissions during high concurrency. JMeter might be overwhelming the local network stack, causing dropped packets that trigger the timeout.
• Implement exponential backoff in your JMeter script to stagger requests. This prevents hitting rate limits on the token endpoint and reduces the chance of gateway timeouts.
• Review the carrier’s SLA for concurrent calls. If the carrier has a lower threshold, the 504 could indicate they are rejecting new sessions due to capacity constraints.

Take a look at at the WFM side of this. While the technical folks are debugging SIP keep-alives, there is often a mismatch between scheduled adherence and actual flow capacity. If your WFM schedules show agents as “Available” but they are actually stuck in a long queue due to flow timeouts, the system might be rejecting new sessions to protect overall health.

Check your schedule adherence reports for the specific shift handling this traffic. If agents are marked “On Break” but the flow is still routing to them, you get these weird timeout errors. Ensure your “Available” status in Architect matches the WFM availability rules.

Adjust the “Collect Input” timeout in Architect to 45 seconds. This gives the WFM engine time to update status before the gateway drops the connection. It usually stabilizes the load during peak hours.