[Mailman-Users] Synchronizing Mailman between two servers.

[Ivan Fetch]

Hello,

    i'm looking at this for our setup as well.  How are others handling 
the Mailman processes (qrunners) starting on a second server once the first 
server has gone down, and switching back to the first server once it has 
recovered?

    Mailman's locks are usually not cleaned up properly when a server 
unexpectedly fails - although we could force the locks to be removed and 
start mailman processes on the second machine, we'll need to be sure that 
the first machine is really "dead".  I assume two machines trying to run 
qrunners on the same mailman directories at once is not a good thing.


    This brings me to search for a way to insure that even if other 
services on a machine are not available, Mailman is certainly not 
operating on the Mailman directories before I try starting Mailman 
processes on a second machine.  Perhaps looking at access / 
modification times of particualr files or directories, relative to the 
current time?  Are there any ideas or comments from others doing or 
looking into this?


- Ivan Fetch.



>>  I'm very interested in the solution you chose, and in how well it works
>>  for you.
>
> 	Sorry, I missed the original message.
>
>>  I'm in the process of designing a fault-tolerant mailman installation,
>>  and any wisdom from experience would be very useful.
>
> 	Generally speaking, I don't think that many people try to do
> this.  You can off-load the web processing with multiple front-end
> web proxies, and you can off-load the mail processing with multiple
> inbound and outbound mail servers (usually best kept as separate
> groups, since the anti-spam, anti-virus, and certain other
> requirements are different for inbound versus outbound use), and the
> rest is just Mailman itself.
>
> 	But, if you do want to go the whole nine yards, the Mailman
> programmers have been pretty careful to keep everything relatively
> NFS-safe, so you should just be able to have an NFS filesystem which
> is then mounted on all of the Mailman servers (preferably served by a
> high availability/redundant NFS server cluster).  Doing things over
> NFS will slow down individual operations, but the overall aggregate
> throughput might be able to be higher, if the NFS server has the
> right architecture and you spread the load out across enough Mailman
> servers, etc....
>
>>>  Any thoughts on what is the best way to synchronize mailman databases
>>>  between to linux boxes?
>
> 	Mailman doesn't really use databases.  At least, not
> out-of-the-box.  There are third-party unsupported patches to allow
> database member adapters, but that's about it.
>
> 	Mailman stores pretty much everything into Python "pickle" files,
> which is a particular binary Python-specific file format that can be
> quickly saved and re-loaded in the native binary format.
>
>>>  If my alias_maps are defined the same in /etc/postfix/main.cf are the
>>>  same on both hosts can I just duplicate my /usr/lib/mailman and
>>>  /var/lib/mailman directories?
>
> 	Duplicate?  What do you mean by "duplicate"?  Just once?  If so,
> then the directories would get out-of-sync.  You'd have to keep all
> the directories in sync somehow.
>
> 	In a nearline backup method, something as simple as rsync would
> suffice, and would potentially only lose any information that was
> written since the last rsync.
>
> 	In a production OLTP type of environment, you'd have to use
> shared filesystems between the sets of machines, and you'd have to
> make sure that those shared filesystems implement all the necessary
> cluster-wide locking facilities, etc... to keep Mailman working
> correctly.
>
> -- 
> Brad Knowles, <brad at stop.mail-abuse.org>
>
> "Those who would give up essential Liberty, to purchase a little
> temporary Safety, deserve neither Liberty nor Safety."
>
>     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
>     Assembly to the Governor, November 11, 1755
>
>   SAGE member since 1995.  See <http://www.sage.org/> for more info.
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