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List:       info-cyrus
Subject:    Re: [POLL] virtual domains and Murder
From:       Fabian Fagerholm <fabbe () paniq ! net>
Date:       2002-07-25 18:26:41
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Rob Siemborski wrote:
> > So why do people want the added overhead of maintaining a murder, if the
> > primary benefit-- the shared namespace across servers, is negated by the
> > fact that virtual domains can't share mailboxes cross-domain?  If a single
> > domain is big enough to span servers on its own, I'm betting you just want
> > a separate murder for it anyway (or bigger servers ;).

But for an ISP or HSP (Hosting Service Provider), it would be too
expensive and require too much set-up time to allocate a separate Murder
for each customer. The same would apply for setting up a separate
standalone Cyrus for each customer. Hence virtual hosting.

What you want is to spend most of the time performing maintenance tasks
(preferably adding mailboxes since that allows you to bill your
customers). When building the system, an ISP/HSP is willing to spend
some time and money setting it up. After that, you want a system that is
dynamic in the sense that you can add more hardware to support a greater
load, and in the sense that you can move mailboxes to a newly installed
piece of hardware and retire an old piece of hardware - preferably
without any downtime at all.

For ISPs/HSPs, the shared mailboxes feature is probably not important at
all, or very close to that.

> From experience admining both a standalone Cyrus and a
> Murder, maintaining the standalone is much simpler, if only because
> the number of components is less. Note that you can still scale cyrus
> to multiple servers using "traditional" IMAP proxys or loadbalancers
> or by playing games with DNS.

Using a separate piece of software, and/or using DNS tricks and/or a
load-balancer, or something along those lines, is seldom attractive (but
is often the only way). Having the load-balancing/scaling logic built
into the mail system itself rids you of maintaining some of those other
pieces. In my opinion, you can't compare a Murder with a standalone
Cyrus. You can compare a Murder with several standalone Cyruses plus
some load-balancing technique. I suspect that the amount of work that
goes into building the latter is greater than the former, and that the
administration involved is equal or less when using Murder. At least,
you only need to learn to use one system.

On Thu, 2002-07-25 at 17:50, Ken Murchison wrote:
> Can we hear from the rest of the virtdomain clan?  Do people have a
> misconception of what Murder does, or are they smarter than Rob and I,
> and see a way to leverage its power/design?

Perhaps it's a misconception, but I immediately saw the benefits of
Murder in other areas than a shared namespace across servers.

First, it certainly is a good alternative to load-balancers or separate
IMAP proxies, partly because it's part of the same software. If you
trust and use cyrus-the-imap-server, then why shouldn't you trust and
use cyrus-the-clustered-imap-server?


My company has been testing an idea that is a little bit more wild:
load-balancing by network topology using Murder. In short, the idea goes
as follows:

Users can genererally be divided into two groups: those that read their
mail from the office (desktops) and those that read their mail on the
road (laptops).

Given a company that has a number of offices and a number of people
working from various places, it would be clever to position their
mailboxes according to where they are most of the time. Hence, you could
place a cyrus Murder backend at each office. Each backend could be as
powerful as needed with regard to the number of users you need to
support at each location. Each backend would include those mailboxes
that belong to the people working at that location.

The mobile users would benefit from a backend positioned close to their
connection point. For example, if they use GSM or GPRS to connect, the
backend would be hosted by the ISP that provides their network service.

Frontends would also be positioned at various places. Using DNS SRV
records, the clients find the correct front-end(s) to connect to.

The advantage of using Murder would be that you can add and remove
front- and back-ends if an office opens, closes or moves, shrinks or
grows - without having to worry about configuring your MTA to use some
look-up technique to determine where the mailbox is. You could move a
mailbox from one backend to another when an employee changes locations.
You could scale up and add back- or front-ends when the number of
mailboxes grow.

Adding virtual domains to the mix would allow the whole system to take
advantage of a few central servers, owned by an ISP/HSP, that host some
mailboxes of all domains, and adding servers located at the customers'
premises as needed that host most mailboxes of the customer's domains
(reducing network traffic going over the slowest links).

Of course, there are a number of issues such as DNS SRV support in
clients, easy and safe moving of mailboxes between backends and so on.

Cheers,
Fabian Fagerholm


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