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From Yehuda Katz <yeh...@ymkatz.net>
Subject [users@httpd] Debugging Intermittent 500 Errors
Date Wed, 06 Sep 2017 00:30:36 GMT
We have set of three servers running Apache 2.4. (version distributed with
RedHat 7) behind a Kemp LoadMaster load balancer. The configuration is
managed by Puppet, so all the servers have the same configuration. I put
the configuration in a Gist to keep the email simple:
https://gist.github.com/yakatz/b406753f6bdc5e19ef5386361afa4b1c

We have several directories that randomly show 500 errors, but when you
refresh, everytthing works fine.
The 500 error is written to the access log on the expected server, but
nothing shows up in any error log on any of the servers.

I suspect this is caused by mod_authnz_ldap because the errors usually show
up upon accessing a page that uses basic auth + ldap for the first time
during the day (or after a long, but undetermined, timeout). The document
root is also on an NFS mount, but we have good logging for NFS and haven't
seen any issues, so I don't think that is the source of the issue.

I know the correct virtual host is being used because I added a custom 500
error page which is being shown and the correct access log is being written
to.

I did not see any documentation about enabling additional logging for
mod_ldap or mod_authnz_ldap, but since most connection have no problems, I
think that will lead to much more noise in the logs.

Is there any other good way to troubleshoot this?

- Y

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