I'm presently utilizing an Apache front-end for my Subversion repository, to be able to do LDAP authentication.

My setup is rather vanilla, however I must have the ability to specify a "backup" LDAP URL, just in case the main the first is lower. I can not presently see a method to do that other then make use of a second location, or virtual host that points in the secondary LDAP server.

Although this would technically work, it's not an optimal solution. I'd like something that doesn't require customers to by hand choose the backup URL.

This really is presently 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

OpenLDAP utilizes a blank separated listing of servers. Presuming that mod_ldap is applying OpenLDAP, this might work:

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

In the event that does not work, try including two blank separated Web addresses:

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

Edit: mod_authnz_ldap appears to aid this formally.