SummaryIn order to avoid the single point of failure in the POA Qmail cluster deployment, Parallels advises you to configure one or more LDAP replication servers which will continue to serve requests when the primary server is failing or is put on maintenance.
ResolutionFollow steps from POA Linux Mail Hosting Deployment guide for the appropriate version of POA to set up the LDAP replication server.
Once it is set up per the Guide, edit /usr/local/qmail/shared/control/ldap_settings file on all the qmail hosts in the cluster and add a comma-separated list of IP addresses to look up the value of LDAP_SERVERS variable like below:
# cat /usr/local/qmail/shared/control/ldap_settings |grep LDAP_SERVERS:After that, edit file /etc/dovecot.ldap.poa_email_auth.conf and /etc/dovecot.ldap.poa_login_auth.conf on the Dovecot host and add a space-separated list of IP addresses to look up the value of hosts variable like below:
cat /etc/dovecot.ldap.poa_login_auth.conf | grep hosts
hosts = 172.16.0.1,172.16.0.2,172.16.10.1
Note that the above changes made manually to Qmail and Dovecot configuration files might get lost during a subsequent POA upgrade. You will need to re-apply them in that case.