"real time" files mirroring ?

[Matthew Seaman]

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On 20/05/2010 15:12:47, Frank Bonnet wrote:

> I'm searching for a software that could perform some kind of real time
> mirroring between two (or more) freebsd servers.
> 
> My meaning is to keep up to date some files ( flat and db maps ) used by
> Postfix on our MX servers and propagate every change of one or more
> files to all the others.

That's actually a very hard problem if you really need /real time/
mirroring.

If you can stand a delay of a few minutes for changes to propagate, then
simply running rsync(1) in a cron job should do -- it's simple to set
up, robust and probably quite a lot faster than you expect.

You will have to handle any issues to do with file locking and having
postfix close and reopen any descriptors on those files if necessary.

Otherwise, there are two strategies to consider:

    * Use a network mounted filesystem.  This can work like a charm, or
      it can be a complete nightmare depending on what postfix needs to
      do with the shared files.  Locking and exclusive access tends to
      be a problem.  You'ld need to look at something like HAST if you
      want a resilient solution, or your fileserver will be a single
      point of failure.

    * Use a network database -- in this case, I'd think LDAP would be a
      good choice.  This is pretty fast in operation, and you can make
      it resilient pretty easily by replicating the database.  Downside
      is extra work when setting everything up.

	Cheers,

	Matthew

- -- 
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
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