Re: virtual host limitations


Subject: Re: virtual host limitations
From: Arthur Corliss (arthur@corlissfamily.org)
Date: Wed Dec 11 2002 - 12:32:35 AKST


On Wed, 11 Dec 2002, Chris Hamilton wrote:

> Can anyone tell me the ballpark number of virtual hosts that is the
> practical upper limit for Apache?

Your constraints on vhost is going to be determined more by your hardware than
by Apache itself. I've worked on hosts that had well over 100 vhosts, though
we're talking about small, low traffic hosts.

The biggest issue is memory. Check the size of your average child memory
footprint (the non-shared portion, in particular), and use that as a metric of
how many concurrent Apache processes you can have at a time. If you're doing
any kind of CGI caching (like using Apache::Registry to cache compiled Perl
scripts), this can be *very* hairy. You really need to think about
restricting such features to most of your vhosts. You also need to look at
what your typical use of CGI that uses spawned processes, etc. You may have
IO constraints as well as memory constraints there.

In short, I've found that the number of vhosts is less important than what
your hardware can support for your connection load, period.

Oh, the one real hard limit you may run into is if you have Apache log to a
different access_log/error_log per vhost, since your OS may offer only so many
file descriptors. The simply solution is to log only to one
access_log/error_log, log the %v field, and use a separate script to split the
entries out for the owner via cron.

        --Arthur Corliss
          Bolverk's Lair -- http://arthur.corlissfamily.org/
          Digital Mages -- http://www.digitalmages.com/
          "Live Free or Die, the Only Way to Live" -- NH State Motto

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