Configuring and Managing Application Server Redundancy
There are two ways the role and function of a Main Application Server can switch to its designated Backup: through an automatic failover (Auto-failover) or through a Manual Takeover. In either case, you must create a Redundancy Group on the iControl—Redundancy configuration page of any Application Server you would like to assign to your group. After the group’s creation, any further configuration, including adding and removing of Application Servers, can be accomplished from the iControl—Redundancy configuration page of any Application Server belonging to this Redundancy Group.
You can enable or disable the Auto-failover function of individual Application Servers in a Redundancy Group. With this function enabled, as long as there is a valid, standby Application Server, configured in a Backup role, a Main Application Server meeting failover criteria switches automatically to the Backup.
In addition, as long as the Backup Application Server is in standby mode, operators can perform a Manual Takeover from any Main in the Redundancy Group to the Backup.
NOTE: To perform Manual Takeovers, you do not need to disable the Auto-failover function of the Main Application Server. |
As there are two independent switching mechanisms (Auto-failover and Manual Takeover), there are system behaviors you should take note of regarding potential conflicts between them, as follows.
IMPORTANT: System behavior |
In the scenario where two or more Application Servers are configured as a Redundancy Group for Auto-failover and there is a condition present that, when detected, will cause an Auto-failover to the Backup, the following system behaviors result: • If a user initiates a Manual Takeover and this is already in progress before the Backup Heartbeat function triggers an Auto-failover, then the Manual Takeover occurs and the Auto-failover is suspended. • If an Auto-failover is already in progress when a Manual Takeover is attempted, then the Auto-failover occurs and the Manual Takeover command is ignored. |