502 and 504 Error differences

Practice is the real truth.

This error has been encountered in the last two times.

For the first time, MySQL takes too long to execute, and at the same time 504, other applications with the same machine deployment appear 502. Reason, the MySQL process CPU utilization is too high, memory consumption, the system does not have time to process the PHP process, resulting in PHP process processing timeout, directly hung off. When other apps are accessed, the link is not on FPM, so 502 appears.

The second time, the data set is slow, multiple refreshes several times, appears 502. Check carefully to find that the PHP process is dead. Restart PHP, link up.

Summarize:

502:nginx Link not on FPM

504:FPM long time no return results, direct timeout