[Mailman-Users] Keeping subscription info in sync across servers

[Richard Barrett]

At 16:41 10/02/2003, Ian Chilton wrote:
>Hello,
>
>Please cc replies to ian at ichilton.co.uk.
>
>
>I was wondering if there was an easy way to keep subscription info in
>sync across multiple list servers.
>
>What I want to do is setup a backup list server which will still
>deliver list mail if the main box is down. So, I only need a single way
>replication, i.e all changes are made on the main server and the 2nd
>server just has to stay in sync.
>
>I was thinking an easy way to do this would be to have a function in
>mailman which made it automatically sent an e-mail or made a socket
>connection to the other server when any options or subscriptions were
>changed.
>
>Is such a thing possible?
>
>
>Thanks!
>
>--ian

Just an idea of how we do things but it may not suit your needs/equipment 
configuration.

Faced with the problem of mailing list server resilience and redundancy we 
turned to NFS and keep almost all of MM's $prefix subtree (all except the 
stuff in $exec-prefix) on shared storage. I do have the advantage of a high 
uptime file server, with all the data security features to act as NFS 
server for this.

I run a live server with a backup server as hot standby, that is, the 
secondary sits there until the primary server breaks and we initiate the 
switchover. This involves a minimal manual intervention.

Basically we switch the MAC address of the machines known as 
primary-mailman-server.our.domain and secondary-mailman-server.our.domain 
in the DHCP config. A brief pause, shutdown the old primary and reboot the 
erstwhile secondary which now comes up with the primary IP number. A little 
conditionality in some of the start scripts means that coming up with the 
primary server IP's number is all that is needed for the new primary server 
to run as such.

A slight pause for the switchover period is OK for us; incoming mail just 
backs up on the MTA's trying to deliver to the Mailman server until the 
switchover completes.

It is a bit crude but it works; had the internal hard drive on the primary 
die a few weeks back and switched over with less than 15 minutes 
interruption in service and no lost mail.

The secondary server does not lie fallow. It has its own MX record and I 
can run test lists on it. I use it (not mounting NFS but using its local 
hard drive for MM's $prefix tree) for checking out new MM software releases 
and getting the wrinkles out before upgrading the primary server in the NFS 
space; the stress when doing a major upgrade to the primary server is much 
reduced having already done it for real as a rehearsal on the secondary 
machine first. The secondary is also used for other non-critical tasks that 
can be suspended if we have to perform a switchover.

If you have other ideas for providing low-cost resilience and redundancy 
for a Mailman server then I would like to hear them.

Cheers

Richard