At the moment, we have a single LDAP server which we are using with LDAP
Account Manager for web-based object management and Atlassian Crowd for
authentication. The LDAP server is queried directly by other servers for
UNIX-level authentication, i.e. SSH and group membership.
I'm looking at introducing a second LDAP server and I'm leaning towards
choosing mirror mode as the replication methodology. Since the only
writes to LDAP come via LAM or Crowd, and these are both web-based, I
think I could set up an almost identical server to the one I have at the
moment and use a system like Amazon's Route 53 DNS service with health
checks to allow me to redirect users off to the second server if the
first server fails.