Failing Over

The failover process, at a high-level, only involves the following steps:

• Stopping Synchronization at the Primary Installation

• Starting Synchronization at the Failover Installation

• Re-enabling the Directory Server Plugins

• Changing the PDC FSMO Role Owner

• Monitoring the Logs

Stopping Synchronization at the Primary Installation

Before starting synchronization at the failover installation, stop synchronization at the primary installation to prevent unwanted interaction between the two systems. Depending on the reasons for failing over this is accomplished in different ways. If the primary Identity Synchronization for Windows installation is still operating properly, for example, failing over because a domain controller or Directory Server is down, then just stop synchronization using the console or idsync stopsync. Otherwise, stopping the Identity Synchronization for Windows daemon (on Solaris) or service (on Windows) on each Identity Synchronization for Windows system that is still operational is recommended.

Starting Synchronization at the Failover Installation

After synchronization is stopped at the primary installation, it must be started at the failover installation using the console or idsync startsync.

Re-enabling the Directory Server Plugins

To complete the failover process, the Directory Server Plugin is re-enabled on each Directory Server, which ensures:

• The plugins running on the masters use the encryption key from the failover installation to encrypt password changes.

• All directory servers receive updated on-demand password synchronization configuration

• Logging done by the plugins is sent to the Central Logger of the failover installation.

The plugins must be re-enabled in this order:

1. Failover installation's preferred master.

2. Failover installation's secondary master.

3. All other masters.

4. All read-only replicas.

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   Note - The order in which the Directory Server Plugins are enabled is important. If they are enabled in the wrong order, on-demand synchronization requests could loop between two masters, tying up all Directory Server connections.

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   When re-enabling the plugins, make sure to specify the configuration directory of the failover installation, for example, config-eu.gt.com

This reinstallation procedure can be automated by doing more work ahead of time:

1. Install the Directory Server Plugins for the Failover configuration.

2. Export the plugins' configuration for each master from the cn=pswsync,cn=plugins,cn=config tree and it includes two entries.

3. Re-enable the Directory Server Plugins for the Primary configuration.

To failover:

1. Delete the cn=pswsync,cn=plugins,cn=config tree.

2. Add the failover installation entries using ldapmodify.

3. Restart the directory server.

Changing the PDC FSMO Role Owner

This step is optional. If the Active Directory Connector in the failover installation is configured to communicate with a domain controller that does not have the PDC FSMO role, then synchronization from Active Directory will be delayed due to the Active Directory replication latency. To avoid this delay, the PDC FSMO role can be transferred to the domain controller that the connector is accessing.

Monitoring the Logs

After the Failover process is complete, monitor the central error log of the failover installation for any unexpected warnings. Warnings similar to the following will likely appear:

[08/Nov/2004:07:58:24.803 -0600] WARNING 25  CNN100 connectors-eu  
"Unable to obtain password of user CN=Jane Test,OU=people,DC=gt,DC=com, 
because the password was encoded by a previous installation of 
Identity Synchronization for Windows Directory Server 
Plugin. The password of this user cannot be synchronized at this time. 
Update the password of this user again in Directory Server."

         

These warnings occur for each password update in the Retro changelog that was made before the Directory Server Plugin was re-installed because the Primary Directory Server Plugin was configured to use a different encryption key from the failover Directory Server Plugin. Many of these password updates were likely synchronized by the primary installation before it went off line, but those that occurred after the primary installation went offline cannot be recovered. These users must change their password either in Active Directory or Directory Server to synchronize their passwords.

Failing Back to the Primary installation

The procedure for failing back to the primary installation is identical.