using slapd-ldap to fail over to upstream servers

[Michael Dean <sysmwd@detir.qld.gov.au>]

hi

we have an openldap 2.1.19 server running on a solaris machine as an LDAP
proxy to three NDS servers. when one of the NDS servers fails the idea is
that the next server in the 'uri' directive will take over ie ..

database ldap
uri "ldap://nds1/o=nds ldap://nds2/o=nds ldap://nds3/o=nds";
idletimeout 600
timelimit 60
threads 128


when 'nds1' is completely offline the cut-over to 'nds2' will work no
worries, but when the 'nds1' server is coming back online or when it gets
overloaded it tends to get swamped with requests from slapd and eventually
slapd will open up it's limit of connections trying to get to 'nds1'
because it thinks it should keep trying 'nds1'

what I think I'd need is something to force slapd to cut over to the next
server in line when requests are taking too long to complete, is this
possible? perhaps a "connecttimeout" might be useful in this situation

or could I do something with conn_max_pending to make it move over to the
next server in the list when too many connections are open to the first
server? or should I lower the timeout settings I've already got even more?

thanks
mike