Runbook: API Not Responding

Symptoms

API requests return 502, timeout, or connection refused.

Diagnosis

# Check service
sudo systemctl status yardpro-api

# Test locally
curl -v http://127.0.0.1:5000/health

# Check nginx
sudo nginx -t
sudo tail /var/log/nginx/error.log

# Check database
mysql -u redrum -p -e "SELECT 1"

Fixes

Problem	Fix
Service down	sudo systemctl restart yardpro-api
DB down	sudo systemctl restart mariadb
OOM kill	Check with dmesg \| grep -i oom