On 31-05-2013 12:57, Patrick Westenberg wrote:
Romer Ventura schrieb:
Scenario1: This should allow any to lose any of the servers and clients still have access to their emails (although I am not sure how the indexes would react to this and sudden disconnection)
2 Dovecot Proxy servers, using a virtual IP to where theclients will connect to from the WAN and LAN
2 Dovecot+Postfix servers with local cacheYour proxy won't reconnect a user to backend B if the backend A fails.
But doesn't that depend on how the vitual IP is managed ie what kind of system is behind it? For example a simple heartbeat setup would correct this at the cost of one machine sitting idle. Other setups using load balancers can correct this.
There is a better solution using the Director service of Dovecot where users are assigned to one of several bacend machines and disconnected when idle. Even, there is a script that monitors the health of the Director backends and adjusts accordingly (which I haven't personally tried yet). See http://wiki2.dovecot.org/Director http://www.dovecot.org/list/dovecot/2010-August/051946.html
Well, I am successfully using Ucarp with apache and Mysql to handle the IP handover if a host is down. I also seem to remember reading that using dovecot proxy and deliver, it can send the user to a different backend if any of them are unreachable. If this is not possible, using keepalive/ucarp (since they are simpler than heartbeat) would solve this.
I try to stay away from clustering specially since XenServer cant do direct LUN to VM like VMWare can and to minimize the painful split-brain issues we would have to add a 3rd server for quorum...
We don’t have a large user base, but being able to shutdown do maintenance on a server during business hours is a plus. We do have a lot of traffic for oure user base, we see around 200K emails per week.
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