About AppEngine object redundancy

You can configure an AppEngine to be a part of a redundant pair. A redundant pair consists of:

• A primary AppEngine. A primary engine is the primary partner of a redundant pair. When you enable redundancy for an AppEngine, it becomes the primary engine.

• A backup AppEngine. A backup engine is the secondary partner of a redundant pair. The backup engine is automatically created by the system when you enable redundancy for an AppEngine and will have the equivalent configuration.

During runtime, an AppEngine that is part of a redundant pair can be considered either "active" or on "standby."

• The active engine is the engine that is hosting and executing ApplicationObjects, DeviceIntegration Objects, and/or Area objects in the runtime environment.

• The standby engine is the engine that is not running any ApplicationObjects, DeviceIntegration Objects, or Area objects. A standby engine is in a passive state while the active partner is up and running. The standby engine monitors the health of the active engine and waits to become active. It will assume the role of the active engine if a failover occurs. In addition, The standby engine can be configured to run in warm-redundancy mode, or in legacy mode.

  • In legacy mode, the standby engine is initialized, started up, and transitions to run onscan at the time a failover occurs. Since initialization and startup phases must occur before the engine starts running, some data loss may occur during failover. Failover may require about a minute, depending on the number of objects and attributes.

  • In warm-redundancy mode, the standby engine is initialized and started up when the galaxy is deployed. The standby engine then runs offscan. When failover to the standby engine occurs, the engine simply transitions to run onscan. This minimizes but does not completely eliminate any data loss during failover, but is typically only a few seconds. Again, the time required for failover to complete is dependent on the number of objects and attributes.

A primary engine can be the active engine, and a backup engine can be standby engine, and vice-versa. It depends on the failover status of the application.

The following are the possible redundancy states for an AppEngine:

• Active

• Active - Standby not Available

• Active - Partner not Upgraded

• Determining Failover State

• Standby - Missed Heartbeats

• Standby - Not Ready

• Standby - Ready

• Standby - Sync'ng with Active

• Standby - Sync'd Code

• Standby - Sync'd Data

• Switching to Active

• Switching to Standby

• Unknown

A redundancy enabled AppEngine communicates with its partner using the Redundancy Message Channel (RMC).

For more information regarding redundancy for AppEngines, see the IDE Help.