What is failover and when does it happen in a clustered Domino server environment?

• A user tries to open a database on a server that is unavailable in the following situations:
  
  
• User double-clicks a database icon on the workspace.
  
  
• User selects a database icon on the workspace and selects File, Open.
  
  
• User selects a database icon on the workspace and selects View - <database view> or Create - <form name>.
  
  
• A user tries to open a database that is unavailable in the following situations:
  
  
• Database is marked out of service.
  
  
• Database is marked pending delete.
  
  
• A user tries to access their home server and the server is unavailable.
  
  
• A user tries to open their mail file and the server is unavailable.
  
  
• A mail router request to transfer and deposit mail to a user's mail file cannot complete because the server is unavailable.
  
  
• A user tries to access a Web Navigator server and the server is unavailable in the following situations:
  
  
• User selects the Open URL icon.
  
  
• User double-clicks a URL hotspot (HTTP address).
  
  
• A user replicates a local database with a database in the cluster and the server is unavailable.
  
  
• A user activates any field, action, or button that contains an @Command (FileOpenDatabase) and either the server or the database is unavailable.
  
  
• A user tries to launch a doclink, view link, or database link that is connected to a database or server that is unavailable.
  
  
• Running a LotusScript routine that includes the DB.OPENWITHFAILOVER call which opens a database with failover if either the database or server are unavailable.

NOTE: Failover does not happen on File, Database, Open.

The following server conditions trigger failover:

• A server is down or unreachable by the user.
  
  
• The server is BUSY. Workload balancing is enabled on a server using the NOTES.INI setting Server_Availability_Threshold and the resources available on the server drop below the specified threshold.
  
  
• The server is MAXUSERS. The server reaches the maximum number of sessions allowed, as specified by the Server_MaxUsers setting.
  
  
• The server is RESTRICTED. The Server_Restricted setting enables the server to deny new open database requests.
  
  

Supporting Information:

The following except is from the Domino Administrator Help, and can also be found in the Administering a Domino Cluster yellow book on pages 7 - 9:

When failover does not occur

Failover does not occur in the following cases:

• When a server becomes unavailable while a user has a database open

• When a user chooses File - Database - Properties or File - Database - Open
  
  
• When the router attempts to deliver mail while MailClusterFailover is set to 0
  
  
• When the template server is unavailable while creating a new database
  
  
• When running agents, other than the mail pre-delivery agent
  
  
• When replicating with a server that is restricted by the administrator or has reached the maximum number of users or the maximum usage level set by the administrator. Also, when replicating with a database marked "Out of Service." Replication occurs regardless of such restrictions, so there is no need for failover to occur.