Predictive Outbound Campaign stalls with 503 Service Unavailable during JMeter load test

Quick question, has anyone seen this weird error? with our Predictive Outbound campaign configuration when subjecting it to concurrent load via JMeter. The goal is to validate the API throughput limits for the /api/v2/predictivedialing/campaigns endpoint before our peak season goes live in New York timezone.

The environment is Genesys Cloud version 2024-09. We are using the standard REST API to update campaign settings in real-time while the dialer is active. The JMeter script is configured with 50 concurrent threads, each performing a PUT request to update the max_concurrent_calls and target_interval parameters. Initially, the requests succeed with a 200 OK status. However, after approximately 45 seconds of sustained load, the response times spike dramatically, and we start receiving 503 Service Unavailable errors consistently.

The error payload indicates that the predictive engine is unable to process the configuration updates due to internal resource constraints. This is unexpected because our account tier supports significantly higher concurrency. We have verified that the WebSocket connections for the agents are stable and not hitting the connection limits. The issue seems isolated to the configuration update API endpoint under load.

We have tried adding a 200ms delay between requests in the JMeter script, which reduces the frequency of the 503 errors but does not eliminate them. The question is whether there is a specific rate limit or throttling mechanism on the predictive dialing configuration endpoints that is not documented in the standard API reference. Additionally, are there any best practices for updating campaign settings dynamically during active dialing sessions without triggering these service unavailable responses? We need to ensure our automated scaling scripts can handle rapid configuration changes without disrupting the outbound flow. Any insights into the internal queuing mechanism for these updates would be helpful.

According to the docs, they say that predictive dialer campaigns have strict rate limits on configuration updates while active, which is likely causing the 503 responses during your jmeter test. updating campaign settings in real-time under heavy concurrent load is not a supported pattern for the /api/v2/predictivedialing/campaigns endpoint. the system is designed to handle call flow logic, not high-frequency config changes.

instead of hammering the api, try using the predictive dialer’s built-in pausing and resuming mechanisms. you can pause the campaign via the api, make your configuration changes, and then resume. this reduces the load on the configuration service significantly. here is a basic flow for that approach:

1. pause the campaign:

patch /api/v2/predictivedialing/campaigns/{campaignId}
{
 "paused": true
}

2. update your campaign settings:

patch /api/v2/predictivedialing/campaigns/{campaignId}
{
 "dialer_type": "predictive",
 "preview_enabled": false
}

3. resume the campaign:

patch /api/v2/predictivedialing/campaigns/{campaignId}
{
 "paused": false
}

this method avoids the 503 errors by ensuring the configuration service is not overwhelmed by concurrent writes. also, consider checking your byoc trunk status during these tests. if the trunks are under load, they might contribute to the instability, although the 503 is primarily an api layer issue. the jmeter script should be throttled to respect the api rate limits, which are typically around 10 requests per second for this endpoint. exceeding this will trigger rate limiting and 503s.