CLUSTERS

Managing failover in a cluster
When you set up a cluster, you create replicas of databases so that users fail over automatically to a different replica if the database or server they try to access is unavailable. In addition, you may want to cause failover to occur intentionally to:
Causing failover to occur

To cause failover to occur, you can use the Server_Restricted setting. This setting tells a server to deny new open database requests and places the server into a RESTRICTED state. This prevents new users from accessing a server, although users who have active connections to databases on the server retain their connections. This setting is useful when you want to do maintenance on a server, upgrade a server, or take a server out of service for another reason. This is also useful when users have failed over to a server and you want them to fail back to the original server.

When a server is in a RESTRICTED state, the Cluster Manager redirects new open requests to other servers in the cluster. When an attempt to redirect is unsuccessful, the user receives an explanatory message and cannot access the server. For each redirection attempt, IBM® Lotus® Domino™ generates a failover event in the log file.

Note The Server_Restricted setting does not affect replication. Replication occurs even when a server is in a RESTRICTED state.

From the Domino Administrator

1. Click the Configuration tab.

2. In the Task pane, expand Server, and then click Configurations.

3. Do one of the following:

4. Click the NOTES.INI Settings tab.

5. Click Set/Modify Parameters.

6. In the Item field, select or enter SERVER_RESTRICTED.

7. In the Value field, enter 0, 1, or 2 where these numbers mean the following:


8. Click Add, and then click OK.

9. Click Save & Close.

From the Web Administrator

1. Click the Configuration tab.

2. In the Task pane, expand Server, and then click Configurations.

3. Do one of the following:

4. Click the NOTES.INI Settings tab.

5. Click Set/Modify Parameters.

6. In the Available Parameters box, click SERVER_RESTRICTED, and then click Add.

7. In the Value field, enter 0, 1, or 2 where these numbers mean the following:


8. Click OK, and then click Save & Close.

From the server console

Send the following IBM® Lotus® Domino™ command from the server console:

set config server_restricted=n

where n can be 1, 2, or 3. These numbers mean the following:


If you want to restrict a server and do not want to wait for all users to close their existing sessions, enter the Drop All command at the console after you put the server into the RESTRICTED state. The Drop All command closes all existing sessions on the server. When users try to reopen the databases they were using, they fail over to a different server, if one is available.

Replacing a cluster server with a different server

If you want to replace a cluster server with a different server, do the following:

1. Set up Domino on the new server.

2. Set the server as RESTRICTED so users won't be able to access it until it is active in the cluster.

3. Create the replicas you want on the new server.

4. Add the new server to the cluster.

5. After the new server becomes active in the cluster, remove the restriction from the new server, and set the old server as RESTRICTED.


6. Remove the old server from the cluster.

Note You can use the Server_Restricted setting for any Domino server. This setting is not limited to clusters.

Other ways to manage failover

If you have set a server to be RESTRICTED or BUSY but have now brought the server back online and want users to fail back to this server, you can make the server that users had failed over to RESTRICTED or BUSY.

You can also set up a server as a backup to another server. You can set the availability threshold to 100 on the backup server so the server is in a BUSY state at all times. This is similar to a RESTRICTED state, except a BUSY server accepts new open requests if no other replica is available, while a RESTRICTED server does not. Therefore, the backup server accepts open database requests only when the primary server is unavailable.