FreeBSD 13 Nginx Worker Connections Exhausted During Traffic Spike

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Clients receive 502/503 or connection reset during high concurrency.

Environment & Reproduction

Appears when worker_connections and file descriptor limits are too low.

ab -n 20000 -c 500 https://host/

Root Cause Analysis

Worker connection ceiling and kernel socket limits are saturated.

Quick Triage

Check active connections and recent nginx errors.

tail -n 200 /var/log/nginx/error.log

Step-by-Step Diagnosis

Review worker_processes, worker_connections, and ulimit settings.

nginx -T | grep -E 'worker_processes|worker_connections'

Solution – Primary Fix

Increase worker and OS limits, then reload Nginx safely.

sudo service nginx configtest && sudo service nginx reload

Solution – Alternative Approaches

Add load balancer tier and reduce keepalive pressure per node.

Verification & Acceptance Criteria

No worker-connection alerts during repeated load tests.

Rollback Plan

Restore previous nginx.conf and limit settings.

Prevention & Hardening

Capacity-test every release and baseline peak concurrency margins.

Related Errors & Cross-Refs

Often coupled with upstream php-fpm saturation.

Related tutorial: View the step-by-step tutorial for freebsd-13.

View all freebsd-13 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Nginx performance tuning on FreeBSD references.