Whenever a new site is added, apache has to be restarted in order to read in the new VirtualHosts with SSL certificates. If only a reload is done with new certificates, apache will complain and say that a full restart is required. So it might just people people adding sites, or it may be some cron as mentioned in the previous post.
You can check if it's DA by having a look at the /var/log/directadmin/system.log
hmm not sure then.... log files are all reasonable size (not really a direct cause although I know a few bits of software dislike it and im sure i have seen a problem with apache and large log files previously)
2004:01:09-11:34:01: service httpd wasn't running, starting it
in the errortaskq.log if apache was down. So it's probably just your users doing their usual stuff, like adding subdomains, ssl certificates, cretaing new users..etc. Those are all things that require.
You can cross check the times of the restarts with the directadmin logs (eg: 2004-Jan-09.log) to see if any commands that were run would do something for a restart. (the command would be run upto 1 minute before the restart).
Reason I asked why DA checked pings or apache would again not leave that though.....
If the max connections gets hit then pings may stop.. therefore directadmin would restart apache if the max connections were high and directadmin was based on pings, however if the sites were static as he said with very little traffic then this is likely not to be the problem.
Apart from the last suggestion.... not to sure what to suggest if the problem is still occuring, possibly a reboot to clean anything up - possibly recompile apache? could be anything
DA just check for the "httpd" process in the /proc directory. Not too sure about speeding it up.. anything that will make it boot faster would be a good thing... maybe comment out the ErrorLogs from the virtualhost templates.. opening a few hundred files might take a while (apache opens, and holds open the error logs. The usage logs are only opened/appended to when needed). Of course, that would stop the logging of errors in their own file...