The Apache mod_status module is something that can be very useful when troubleshooting high CPU or Memory usage with Apache.

Taken it directly from the Apache documentation:

– The number of worker serving requests.
– The number of idle worker.
– The status of each worker, the number of requests that worker has performed and the total number of bytes served by the worker.
– A total number of accesses and byte count served.
– The time the server was started/restarted and the time it has been running for.
– Averages giving the number of requests per second, the number of bytes served per second and the average number of bytes per request.
– The current percentage CPU used by each worker and in total by all workers combined.
– The current hosts and requests being processed.

Setting it up is simple.

# CentOS 6 / CentOS 7
[root@web01 ~]# vim /etc/httpd/conf.d/status.conf

# Ubuntu 12.04
[root@web01 ~]# vim /etc/apache2/conf.d/status.conf

# Ubuntu 14.04
[root@web01 ~]# vim /etc/apache2/conf-available/status.conf

Using the correct location for your distro use the following configuration to enable mod_status. Update the AuthUserFile line accordingly for your distro:

<IfModule mod_status.c>
#
# ExtendedStatus controls whether Apache will generate "full" status
# information (ExtendedStatus On) or just basic information (ExtendedStatus
# Off) when the "server-status" handler is called. The default is Off.
#
ExtendedStatus On

# Allow server status reports generated by mod_status,
# with the URL of http://servername/server-status
# Uncomment and change the ".example.com" to allow
# access from other hosts.
#
<Location /server-status>
     SetHandler server-status
     Order deny,allow
     Deny from all
     Allow from localhost ip6-localhost
     <IfModule mod_rewrite.c>
          RewriteEngine off
     </IfModule>
     Allow from 127.0.0.1

# On CentOS / RedHat systems, uncomment the following line
     AuthUserFile /etc/httpd/status-htpasswd

# On Debian / Ubuntu systems, uncomment the following line
#     AuthUserFile /etc/apache2/status-htpasswd

     AuthName "Password protected"
     AuthType Basic
     Require valid-user

     # Allow password-less access for allowed IPs
     Satisfy any
</Location>

</IfModule>

Once you have the configuration in place, you can secure it with a username and password:

# CentOS 6 / CentOS 7
[root@web01 ~]# htpasswd -c /etc/httpd/status-htpasswd serverinfo
[root@web01 ~]# service httpd restart

# Ubuntu 12.04
[root@web01 ~]# htpasswd -c /etc/apache2/status-htpasswd serverinfo
[root@web01 ~]# service apache2 restart

# Ubuntu 14.04
[root@web01 ~]# htpasswd -c /etc/apache2/status-htpasswd serverinfo
[root@web01 ~]# a2enconf status.conf
[root@web01 ~]# service apache2 restart

Now go to:

http://serverip/server-status

You can have the /server-status page refresh automatically by using the following in the URL:

http://serverip/server-status?refresh=2

It may give you some idea of what client, or what types of requests, are causing the resource contention issues. Usually it is a specific web application misbehaving, or a specific client is attacking a site.