Outbound Campaign Fails with 403 Forbidden on High Concurrency

General Discussion
1

Is it possible to configure api_key rotation within JMeter to bypass the 403 Forbidden errors we encounter when simulating 100 concurrent outbound calls? The POST /v2/outbound/campaigns endpoint returns a 403 with message Rate limit exceeded despite using the correct OAuth credentials for the US-East region.

2

The official documentation states that rotating API keys within a single JMeter execution plan is not the correct approach for handling 403 Forbidden errors caused by rate limiting. The 403 status code with the message “Rate limit exceeded” indicates that the platform API has hit its concurrent request threshold, not that the authentication credentials are invalid or expired. For an AppFoundry integration handling high-concurrency outbound campaigns, the platform enforces strict rate limits on the /v2/outbound/campaigns endpoint to protect system stability.

To resolve this, you need to implement a backoff strategy in your JMeter script rather than key rotation. The most reliable method is to use the HTTP Request Defaults or a BeanShell PostProcessor to capture the Retry-After header from the 403 response and pause the thread accordingly. Alternatively, you can stagger the start times of your JMeter threads using the Thread Group’s “Ramp-Up Period” setting. For 100 concurrent calls, a ramp-up of at least 60 seconds is recommended to avoid hitting the burst limit.

Here is a sample BeanShell code snippet to handle the retry logic:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

String retryAfter = prev.getResponseHeader("Retry-After");
if (retryAfter != null) {
 try {
 int sleepTime = Integer.parseInt(retryAfter) * 1000;
 Thread.sleep(sleepTime);
 vars.put("RETRY_COUNT", String.valueOf(Integer.parseInt(vars.get("RETRY_COUNT")) + 1));
 return true;
 } catch (Exception e) {
 log.warn("Failed to parse Retry-After header: " + e.getMessage());
 }
}
return false;

Ensure your OAuth token is valid and has the necessary outbound:campaign:write scope. A common fix is to monitor the X-RateLimit-Remaining header to proactively slow down requests before hitting the limit.

  • OAuth token expiration and refresh mechanisms
  • Platform API rate limit headers (X-RateLimit-Limit, X-RateLimit-Remaining)
  • JMeter Thread Group ramp-up configuration
  • Exponential backoff algorithms for API resilience
3

It’s worth reviewing at implementing a simple retry loop with exponential backoff in your JMeter test plan. In Zendesk, we often hit similar walls during bulk imports. The 403 here is strictly a rate limit, not an auth issue.

Rate limit exceeded

Adjusting the throttle controller is usually the quickest fix for this.