503 Service Unavailable: The server is currently unable to handle the request due to temporary overloading or maintenance of the server.
we are running a load test for predictive outbound campaigns. using jmeter 5.6.2 to simulate 500 concurrent calls hitting the /api/v2/outbound/campaigns endpoint. the goal is to check the capacity of the predictive dialer.
the error happens when we try to update the campaign settings in bulk. specifically the dial_rate and answer_machine_detection settings. we get the 503 error after about 2 minutes of running the test. the cpu usage on our load generator is fine. but the genesys cloud api seems to drop the connections.
is there a limit on how many predictive campaigns can be updated at once? or is this a global rate limit for the outbound api? we are using the default tenant settings. no special configuration.
please help. we need to know if this is a bug or if we need to adjust our jmeter thread groups. the documentation says the api is rate limited but does not specify the exact limits for predictive routing updates. we are in the us-east-1 region. time zone is et.
{
“thread_id”: “12345”,
“post_content”: “Adjust the JMeter thread group configuration to mimic the natural pacing of Zendesk API imports. In Zendesk, bulk ticket updates often required careful throttling to avoid hitting rate limits, and Genesys Cloud behaves similarly. The 503 Service Unavailable error typically indicates the predictive dialer engine is overwhelmed by simultaneous state changes. Try reducing the concurrent threads to 50 and adding a Random Timer between 500ms and 2000ms to simulate human-like interaction patterns. This prevents the sudden spike that triggers the 503 response during the /api/v2/outbound/campaigns update.”
}
When migrating from Zendesk, teams often forget that Genesys Cloud’s predictive dialer calculates **dial_rate** and **answer_machine_detect** thresholds in real-time across all active campaigns. Bulk updates can cause temporary calculation lags, leading to the 503 error. Ensure your JMeter test script includes a **Ramp-Up Period** of at least 30 seconds for 500 users. This gradual increase allows the Genesys Cloud backend to process the campaign state transitions without overloading the service. Additionally, check the **Campaign Status** before updating; only modify campaigns in a **Paused** or **Stopped** state to avoid conflicting with live dialing operations. This approach mirrors the careful bulk update strategies used in Zendesk, ensuring a smoother transition and more accurate load testing results.