Is there an ldap C/C++ library that provides fail over?

Question

I'm looking for an LDAP libracy in C or C++ that allows me to specify a list of LDAP hostnames instead of a single hostname. The library should then use the first one it can connect to in case one or more of the servers is/are down. I'm sure it'd be easy to wrap an existing library to create this, but why reinvent the wheel?

Answer 1

I can't say I've ever heard of one. Furthermore, most LDAP-capable software I've used supported failover poorly or not at all. You might be better off trying to implement the failover at the server, by putting it behind a load balancer or similar.

Answer 2

Putting the server behind a load balancer creates a single point of failure, which is what I'm trying to avoid in the first place.

Answer 3

Use multiple A records, each with a different IP.

ldapserver.example.com.    IN A    1.2.3.4
ldapserver.example.com.    IN A    2.3.4.5

The OpenLDAP client libs will try each host in turn. Failover is (unfortunately) as slow as your TCP connection timeout...

Answer 4

The novell cldap libraries (and java libraries) support a list of space separated hosts when connecting. It'll try each one in turn, as noted in the ldap_init() page.

The openldap libldap library also supports a space separated list of hosts passed to ldap_open() or a comma separated list passed to ldap_initialize().

The only catch is to make sure to handle the LDAP_SERVER_DOWN error that gets returned after a connection goes away. I usually write a wrapper function that tries an operation (ie: a search), and tries to reconnect if LDAP_SERVER_DOWN occurs, and then does the operation again.