Trying to understand why our BYOC trunk registration fails with a 503 Service Unavailable error when JMeter hits 200 concurrent SIP INVITEs. The environment is Genesys Cloud EU-West-1. Standard config works fine at 50 calls. At 200, the edge returns 503 immediately. Is this a hard limit for new accounts? We see no 429 rate limit errors, just connection refused. Sharing the JMeter thread group config below. Any ideas on capacity thresholds?
TL;DR: This looks like a platform capacity issue, not a recording problem.
The 503 indicates the edge is overloaded; check your account’s concurrent call limit in the admin console.
Have you verified the specific concurrent media session limits configured for your tenant? The 503 response often indicates that the edge node has reached its allocated processing capacity rather than a simple registration failure. While the suggestion above correctly identifies a capacity constraint, it is important to distinguish between the soft limit for standard operations and the hard ceiling for high-volume load testing.
In Genesys Cloud, new or intermediate-tier accounts typically have lower default thresholds for simultaneous SIP INVITEs to prevent resource exhaustion. You should check the “Capacity and Limits” section in the Admin portal. If your current allocation is below 200 concurrent sessions, the platform will reject excess traffic with a 503 error. Consider requesting a temporary limit increase from Support for the duration of the spike test. See KB-8921: Understanding BYOC Capacity Thresholds for detailed guidance on adjusting these parameters.
This is caused by edge overload, not just account limits. You are hitting the hard ceiling mentioned. In my React Native apps, I throttle WebSocket reconnections to avoid this. Check your concurrent_sessions_limit in the admin console. If it’s low, increase it or stagger your JMeter ramp-up.
This is typically caused by the edge node rejecting new WebSocket subscriptions when the underlying TCP connection pool is saturated, not just SIP INVITE volume. The 503 here is a transport-layer rejection. When you hammer 200 concurrent threads, you are likely exhausting the ephemeral ports or hitting the WebSocket handshake rate limit before the SIP signaling even completes.
Cause:
The Genesys Cloud Edge enforces strict limits on concurrent WebSocket connections per tenant to prevent resource exhaustion. The Notification API uses persistent WebSocket connections. If your JMeter script opens a new WebSocket for each call flow without proper pooling or reuse, you hit the connection ceiling. The 503 is the edge dropping the HTTP Upgrade request.
Solution:
Stop opening a new WebSocket per call. Use a single shared WebSocket connection for event streaming and multiplex channels. Here is the minimal reconnect logic you need to handle gracefully:
let ws = null;
const reconnect = () => {
ws = new WebSocket('wss://api.euw1.genesyscloud.com/api/v2/analytics/events');
ws.onopen = () => {
// Subscribe to specific channels only
const sub = {
type: 'subscribe',
channels: ['/v2/analytics/interactions/conversations/voice']
};
ws.send(JSON.stringify(sub));
};
ws.onclose = (e) => {
if (e.code !== 1000) {
setTimeout(reconnect, Math.min(Math.random() * 2000 + 1000, 10000)); // Exponential backoff
}
};
};
reconnect();
Verify your concurrent_sessions_limit in Admin > System > Telephony. If it is at default (usually 50-100), you must request an increase. Stagger your JMeter ramp-up to 10 calls/sec instead of 200 at once. The edge needs time to allocate media resources. Check the x-genesys-cloud-trace-id in the 503 response to trace the specific edge node failure in the support console.