We have a client with two mailbox and two MTA servers. One of the mailbox servers is the LDAP master and each of the MTA servers runs an LDAP replica.
Normally when we do a multi-server upgrade we shut all of the Zimbra servers down first before we start by upgrading the LDAP master.
This client however is very keen to minimize downtime, and has asked if the following is doable:
- Close http/s ports on the firewall and shutdown both mailbox servers.
- Sever the network connection between the MTA/LDAP replica servers and both mailbox servers.
- Upgrade the mailbox servers (LDAP master first) while allowing the MTA servers to continue to queue incoming email.
- After upgrading the mailbox servers (now running), shutdown the MTA servers and close smtp/submission ports on the firewall.
- Re-establish the network connection between the MTA servers and mailbox servers and upgrade the MTA servers.
We have never done that before ourselves. How does this sound? Has anyone done this before?