I’m completely stumped as to why my JMeter script hits 429 Too Many Requests on the /api/v2/outbound/campaigns/{id}/contacts endpoint after 200 concurrent requests, even though the global API rate limit should allow higher throughput.
The campaign is configured with predictive dialing mode:
campaign:
mode: PREDICTIVE
concurrency: 50
agentAllocationStrategy: MAXIMUM
The error occurs specifically when the JMeter thread group exceeds the predicted agent capacity, suggesting a mismatch between the load test configuration and the Genesys Cloud predictive routing limits. Has anyone seen this specific throttling behavior when simulating high-volume contact uploads?
Check your API rate limiting strategy and the specific endpoint throttling rules for outbound campaigns. The /api/v2/outbound/campaigns/{id}/contacts endpoint is heavily guarded, especially when dealing with predictive dialing modes. The 429 errors you are seeing are likely not a global limit issue, but rather a specific throttling mechanism triggered by the high concurrency of contact ingestion attempts. When a campaign is set to PREDICTIVE with MAXIMUM agent allocation, the system expects a steady stream of contacts, but JMeter’s burst behavior can overwhelm the ingestion queue.
The global API rate limit applies to general REST calls, but outbound contact operations have separate, stricter limits to prevent database contention. This is a common gotcha when load testing predictive campaigns; the system prioritizes call stability over bulk data ingestion speed.
To mitigate this, adjust your JMeter script to implement exponential backoff on 429 responses. Instead of retrying immediately, add a delay that doubles with each consecutive 429 error. Additionally, consider breaking your contact list into smaller chunks and staggering the upload times. Here is a sample configuration for the HTTP Request Defaults in JMeter:
<HTTPSamplerProxy>
<element name="Timeout">30000</element>
<element name="ConnectTimeout">5000</element>
<element name="RetryInterval">1000</element>
<element name="MaxRetries">3</element>
</HTTPSamplerProxy>
Also, verify that your campaign’s concurrency setting aligns with the actual agent capacity. Setting concurrency: 50 while pushing 200 concurrent API requests creates a mismatch between dialing capacity and data ingestion. Reducing the JMeter thread count to match the campaign’s effective throughput, or using a constant throughput timer to cap requests at 50 per second, should stabilize the connection. This approach mirrors how we handle SIP registration bursts across our BYOC trunks-smoothing the ingress to avoid carrier-side drops.