Currently, I use a DNS RR set with three A entries for my LDAP master
server and its two replicas, but this is inefficient on those machines
that have a local server, because they only use it on 33% of all queries.
Further, queries become very slow if a remote server is down, but the
local server works.
DNS SRV records solve the problem, apart from the fact that I am not
aware of them being used anywhere.
A hacked name server that offers ordered RR sets would also solve the
problem, but I prefer to stick with standard DNS.
The third solution is to extend LDAP URLs in Exim to support multiple
hosts like ldap://hosta,hostb/cn=foo,dc=bar?attr. If hosta can not be
reached, hostb is tried. To be more precise, if the lookup with hosta
would defer the mail, a lookup with hostb would be made. If the lookup
failed with hosta, hostb would not be tried (because a failure means
that the lookup itself was successful).
While reading the ldap.c lookup code in Exim, I saw that too few entries
cause a search to fail (which is ok), but too many defer it. Why? The
search itself was successful and the result is only as likely to change
in future as for searches with no entries.
Are there any objections against extending the LDAP URLs for exim? If not,
I might send a patch later.
Michael
--
*** Exim information can be found at
http://www.exim.org/ ***
