Dual communications channel failure consideration

A redundant AppEngine system configuration provides high availability in the event of a single communication channel failure. This means that the system will gracefully handle situations where only one communication channel fails at a given time; for example, PC failure, Primary network failure.

The role of the RMC as a dedicated link to synchronize data and monitor the status of the redundant pair minimizes the chances of failures within the system, since it is a dedicated cross-over cable between two computers and does not carry external data traffic.

If the active AppEngine simultaneously loses the connection to the pPrimary network and to the RMC, the system reverts to an ACTIVE-ACTIVE state.

To recover from an ACTIVE-ACTIVE condition, both connections must be reestablished. The system arbitrates assigning the Active state, so that the Primary server will become Active, regardless of its state before the ACTIVE-ACTIVE condition.

It is possible to design the application to handle the ACTIVE-ACTIVE condition. The solution includes scripting and a third component to monitor the status of both engines. For example, a condition script could be implemented in the PLC to monitor the status of both engines and arbitrate which one stays active if a simultaneous failure occurs in the RMC and primary network.