Apache Backup LDAP Repository with mod_ldap

Question

I am currently using an Apache front end for my Subversion repository, in order to do LDAP authentication.

My setup is fairly vanilla, however I would like to be able to specify a "backup" LDAP URL, in case the primary one is down. I can't currently see a way to do this other then use a second location, or virtual host that points at the secondary LDAP server.

While this would technically work, it is not an optimal solution. I would like something that does not require users to manually select the backup URL.

This is currently Apache 2.2.3 on CentOS 5.

Sample entry from httpd.conf:

<VirtualHost *:80>
 ServerName svn.example.com
 ServerAlias svn.example.com svn

 <Location /erx>
  DAV svn
  SVNPath "/usr/local/svn/repos"
  Require valid-user
  AuthzSVNAccessFile "/usr/local/svn/conf/svnaccess.conf"
  AuthName "SVN Repository"
  AuthBasicProvider ldap
  AuthType Basic
  AuthzLDAPAuthoritative off
  AuthLDAPURL "ldap://ldapserver:389/searchstring" NONE
  AuthLDAPBindDN "bind"
  AuthLDAPBindPassword password
 </Location>
</VirtualHost>

Answer 1

OpenLDAP uses a blank separated list of servers. Assuming that mod_ldap is using OpenLDAP, this may work:

ldap://primary.server backup.server:389/searchstring

If that doesn't work, try including two blank separated URLs:

ldap://primary.server:389/searchstring ldap://backup.server:389/searchstring

Edit: mod_authnz_ldap seems to support this officially.