Every once in a while a page made available on the apache server is not available. After a few minutes everything is working (the party is often visited). How can I establish what this problem results from (how to read it from logs)?
start looking at /var/log/apache2/error.log [in debian world. possibly it's different location in settings of server/vhost ].
also enable status page and try to poll it automatically every say 30 sec and dump to disk - maybe your appache has limits for number of parallel connections it can handle and you run out of them?
install munin and start gathering statistics - maybe your machine swaps to death? surly monitoring tools will not help you when machine is dying but will show you trends.. you'll have some trace what happened just before the hiccup.
possibly you experience networking issues... does ssh / ping work when apache does not respond?
I think I deciphered what you are asking...
Try using Apache's mod_status to see what it is doing.
In the httpd.conf file:
Restart apache and see what is happening. My guess is you are breaching the max clients limit.