Re: Mail servers for large numbers of users
On Sun, 12 Dec 1999, William Burrow wrote:
> > You can not equate http and imap in this manner. http serves files. You
>
> Why not. An email resides in a file. In a Maildir setup, exactly one
> message resides in one file. With Unix mailbox format, several messages
> exist in one file, big deal.
The differences are access permissions. Try building a web server with
>64K virtual domains on a Linux box with write access granted to a single
user to each domain's space and you can run into a similar problem.
Launching a separate instance of the server chrooted to each user's
directory is one answer but gets pretty expensive once you get more than
1000 copies of the server running at once :)
> You can't get from http://www.virtualOne.com to http://www.virtualTwo.com
> from from http://www.virtualOne.com by typing paths (other than a link
> directly to virtualTwo's site).
Which is what I thought I said. There is sometimes another way. Lets say
your main doc root is /var/www and you have two domains ... foo.com and
bar.com and you put one in /var/www/foo and one in /var/www/bar.
I can type either:
www.foo.com OR I can type http://<real-server-name>/foo/index.html and get
the same file on many servers. In other words, if I use the real server
name and if I know the actual path to the document root, I can access it
directly.
> Do that with ONE UID. Courier-IMAP does this. All users must access
> their mail through IMAP. It makes sense. It works. It is the way it
> is done.
Ok fine. Have you ever seen a linux box with several THOUSAND users logged
in at once? Have you ever seen what happens when an ENTIRE organization
can not access email (I have). It is a Bad Idea. Cheap maybe but it will
not perform worth a crap and is not worth doing that way. Sure for 10-50
users ... no problem ... for >65,000 users ... THINK, man. Anyone
proposing such a solution would get laughed out of town. It will work on
paper ... maybe ... if you can have enough processes and open files and
RAM and CPUs. SO I suppose you can go out and get a 12 CPU Sun E10000 to
run this on or you can use a farm of cheap Intel Linux boxes.
> > directory and read their mail. This is why it breaks when you have more
> > users than you have bits to assign unique user ID's.
>
> You can't do this because the path you specify is not associated with
> your IMAP login ID. The database tells the server what is the
> acceptable base path. The path is logically constructed, so it is easy to
> tell apart illegal paths from legal paths. The scenario you present is
> all in your head.
Ever set up IMAP in Netscape Navigator or Sun ROAM or Eudora? You must
tell it the path to your mail directory. It does not get the path from the
server, it tells the server what the path is. Sure, if the server is in a
chroot environment, all users can give their client the same path ...
/mail ... but now you need a separate instance of the IMAP server for each
client logged in. How many gig of RAM does the server have? Lets just
imagine that it is a Tuesday afternood and 25% of the users have their
IMAP client active. That would be somewhere just over 16,000 users. That
is being conservative. Most people start their email client when they
arrive at work and do not close it until they go home.
What kind of machine are we talking about here? Certainly not an Intel
box.
Reply to: