Question

We have multiple LDAP/domain servers.(ex. LDAP://server1.com:389/DC=server1,DC=COM, LDAP://server2.com:389/DC=server2,DC=COM) I need to use one of them by checking availabilty.

try {
    Hashtable<String, String> env = new Hashtable<String, String>();
    env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.ldap.LdapCtxFactory");
    env.put(Context.PROVIDER_URL, "LDAP://server1.com:389/DC=server1,DC=COM");
    env.put(Context.SECURITY_AUTHENTICATION, "simple");
    env.put(Context.SECURITY_PRINCIPAL, username);
    env.put(Context.SECURITY_CREDENTIALS, password);

    DirContext ctx = new InitialDirContext(env);
} catch(NamingException ex) {
}

Answer 1

You can perform a simple anonymous search to see if the LDAP server is up and running. If you get a Connection refused exception, then the server would be down and you can switch to the next one in your list, perform the same operation again.

Usually there would be load balancers sitting in front of a string of domain controllers, the requests are routed to the load balancer which would identify the right DC and proxies the request to it. The LB takes care of periodically checking the availability of DCs in its list, remove them if they went down, check them back again when they are on etc.,. You may want to check with your IT department about existence of such an LB in your environment.