ugh. my site has been running fine for months on Nginx + PHP-FPM 😅 now it falls over every few hours at random and all visitors get this:
502 Bad Gateway
nginx
Restarting everything brings it back, until it doesnt :) Im not a full-time sysadmin, i set this up from a tutorial and it just worked. Now Im staring at log files i barely understand. Which log should i look at first, and what am i looking for?
been there man a 502 means the proxy reached out to teh app behind it and got a broken or no response. Read the proxy's error log first: sudo tail -n 100 /var/log/nginx/error.log for Nginx. connect() failed (111: Connection refused) means nothing is listening; upstream prematurely closed connection means the app crashed or kliled the request mid-way. hope that helps :)
lol same thing happened to me check the app service right after a 502: systemctl status php*-fpm, systemctl status yourapp, or docker compose ps. If it shows restarts or exited state, read its own logs with journalctl -u yourapp -n 200 or docker compose logs app, the real error lives there, not in the proxy log.
lol same thing happened to me look for teh kernels OOM killer: dmesg -T | grep -i -E 'killed process|out of memory'... small VPSes kill PHP-FPM workers, Node or database processes under load, which produces 502s during traffic spikes. add swap, reduce worker counts, or move to a bigger plan.
@solsen-2ud WOWWW it was the OOM killer. added a swap file and lowered the worker count. no 502s for a week now on Nginx + PHP-FPM. thank you!
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