apache error analysis

Question

"502 bad getway" appeared on the web server today

Use: service httpd restart Restarting apache is useless.
Finally, stop and then start: service httpd stop, service httpd start and that’s it.

Checked the access log and error log and found nothing unusual.

Are there any logs or instructions that can be used to discover or check what happened at that time?

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Because I used Alibaba Cloud Cloud Shield, 502 should be the error code returned by Cloud Shield.

Answer 1

502 Description Apache, as a proxy (or gateway), encountered an error when communicating with its proxy's back-end server. Specific error information is generally provided in the error log.

Answer 2

502 refers to invalid gateway or wrong gateway.
Generally, when the web server receives the http data stream, it will be recorded. If everything in the Apache error log is normal, it may be caused by your server hanging up or suspended animation.

Answer 3

502 is first of all a server problem, wget http://localhost, see if it is 502, put a static file under the webroot and see if it can be accessed. If it can, then there is a problem with your application app