Tuning guides talk about throughput. Nobody pages you about throughput. They page you about symptoms, and the useful skill is mapping a symptom back to a cause before you spend money on hardware. Three failure modes account for most of what I find on inherited servers. Each has a distinct signature. The 502 nobody can reproduce Server has 8GB. PHP-FPM is set to 100 workers. Each worker uses 60MB under load. That's 6GB of PHP, plus MariaDB, plus Nginx, plus the OS. Under nor...