So I’m seeing a very odd bug with the /api/v2/architect/flows endpoint during our latest load test. we are hitting a 503 service unavailable error specifically when the concurrent session count exceeds 400. the environment is gc version 2024-12. we are using jmeter 5.6.2 with a simple ramp-up of 200 users over 60 seconds. the flow itself is very basic, just a gather input and transfer. it works fine at 100 concurrent users. but as soon as we push past 400, the api starts rejecting requests. we have checked the websocket connection limits and they seem to be within the standard tier limits. is there a specific rate limit for flow execution that we are missing? or is this a known issue with the architect service under high load? we need to validate our capacity planning for a new client. any help would be appreciated. here is the jmeter thread group config we are using:
The 503 error indicates a capacity threshold rather than a configuration flaw in the flow logic. Verify the concurrent session limits assigned to the specific queue or route group, as the default tier often caps out well below 400 simultaneous interactions. Adjust the resource allocation in the admin console to match the expected load profile.
TL;DR: Check WebSocket backpressure and JMeter thread group settings before blaming flow capacity.
The documentation actually says that 503 errors on /api/v2/architect/flows during high concurrency often stem from connection pool exhaustion in the client, not just server-side queue limits. While the previous answer mentions queue capacity, the real bottleneck in JMeter 5.6.2 is usually how the HTTP Request Defaults handle keep-alive connections under load. If you are hitting 400+ threads, the default JMeter config might be dropping connections faster than Genesys Cloud can handshake them, leading to a 503.
Try adjusting your JMeter HTTP Request Defaults. Set Connection Timeout to 10000 and Response Timeout to 30000. Crucially, ensure Use KeepAlive is checked. Then, in the Thread Group, reduce the number of threads per controller but increase the loop count to maintain total throughput without opening too many simultaneous sockets.
Here is a sample JMeter config snippet for the HTTP Request Defaults:
<elementTestPlan>
<elementProp name="HTTPSamplerDefaults.gui" elementType="TestBeanGUI">
<stringProp name="TestPlan.gui.title">HTTP Request Defaults</stringProp>
</elementProp>
<elementProp name="HTTPSamplerDefaults" elementType="TestBean">
<stringProp name="HTTPSampler.path"></stringProp>
<boolProp name="HTTPSampler.use_keepalive">true</boolProp>
<intProp name="HTTPSampler.connect_timeout">10000</intProp>
<intProp name="HTTPSampler.response_timeout">30000</intProp>
</elementProp>
</elementTestPlan>
Also, verify you are using the correct region endpoint. If you are testing from Singapore staging, ensure your base URL points to api.genesys.cloud or the specific staging host. Mismatched endpoints can cause immediate 503s when the load balancer rejects unknown origins. Start with 50 threads and ramp up by 50 every minute to see where the curve breaks. This isolates whether it is a rate limit or a socket issue.
Make sure you treat the JMeter thread group like a Zendesk ticket macro, reusing connections instead of creating new ones for every request. Switching to non-HTTP samplers for WebSocket handshakes usually resolves the 503s faster than tweaking queue limits.