failover scenario's for replication
wes at umich.edu
Mon Aug 28 14:23:22 EDT 2006
On 26 Aug 2006, at 16:09, Paul Dekkers wrote:
> Right now, it looks tricky to me to enable replication after failover,
> or the replicated machine itself if you're not sure that the
> replica is
> identical and the sync-processes finished completely: if a message-
> is in place on machine A (say "7.") but it was not replicated to
> B while that one becomes the master, the machine B will create a new
> file 7. and both machines consider this file synchronised after that:
> also if roles switch back, you have two different (with one isolated)
> copies of 7.
As I understand it, this is what replication uuids are for. Not that
I've experimented with this particular case.
> Or is it only preferred to use a replica if there is a really serious
> crash on the (previous) master?
That's certainly how I view the current system. Until replication is
more reliable, I'd be quite leery of any sort of automatic failover.
> It sounds nice to me if I could use heartbeat or (u)carp (/ifstated)
> like systems to start and stop a sync_client or sync_server copy of
> cyrus (both different cyrus.conf) as soon as the state of the virtual
> interface changes, but then it is even more likely that some
> process is not finished without an admin even noticing it.
I agree, this is a great goal. I'd be interested in seeing a roadmap
for how to achieve it, including how failback would occur. There's a
lot of opportunity to share operational experience with Cyrus. If
only there was a forum to publish such information...
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