Server Redundancy Principles of Operation Summary

In a normal state:

• The primary is in control or is the active server.
• The secondary is the standby server.
• The primary keeps the secondary Alarm, Point and User information synchronized.
• Viewers collect data from the primary computer.

When the primary fails:

• The primary is off line.
• The secondary becomes the active server.
• Viewers collect data from the secondary computer.

When the project on the primary is restarted :

• The primary obtains Alarm and User information from the secondary and automatically takes over these functions.
• The secondary continues to provide and collect point data for the viewers and the primary for synchronization.

Example

In the following case:

• The primary and secondary are running in a server redundant pair,
• There is a temporary network interruption between the two that exceeds the heartbeat timeouts and retries for the two nodes,
• The primary is restarted,

both the primary and secondary will assert themselves as active.

When the network recovery occurs, the two servers will negotiate to decide which will be the active and which will be the standby. Thus, the primary as the standby, and the secondary will be the active. You cannot choose which of the two nodes in the redundant pair will be the active after a dual active recovery; it will always be the secondary.

After a system manager resets the primary:

• The primary collects point data and takes over point management as well as all other project functions.
• The secondary returns to standby mode.