Duplication is not independence
Two servers on one switch, storage array and power source retain major shared failures. Map every dependency required for execution. Redundancy only covers failures actually separated; it does not automatically protect against configuration errors or replicated corruption.
Create a matrix of failure, impact, detection, surviving component and return procedure. Include identity, queues and equipment interfaces, not only WCS processes.
Active-passive and active-active
Active-passive simplifies command ownership but needs proven takeover. Active-active may distribute distinct resources, while requiring explicit ownership and shared-state coordination. Two copies of the same logic do not by themselves form a correct redundant system.
Quorum can support leadership decisions, but the losing instance must also lose command authority. Preserving consistency during a partition may require stopping part of the service. Document that choice.
Replication is not backup
An accidental deletion can propagate to every replica. Backup addresses recovery to an earlier trusted state. Protect retention against administrative errors and incidents affecting the whole environment.
Standby configuration must follow changes. Adapter, certificate or equipment-map drift may surface only during failover. Validate configuration as part of maintenance.
Worked shared-switch failure
Both servers remain powered but lose PLC connectivity through a shared switch. Application failover cannot restore that path. An alternative supported and tested path is needed, or the failure domain must be explicitly accepted.
Remove dependencies individually and observe the complete service. Test failback too: returning to the original component can cause another interruption. Document coverage and final integrity checks.
Project verification criteria
- Identify shared power, network and storage.
- Test quorum loss and prevention of competing commands.
- Validate standby configuration and failback.
Examples describe engineering decisions and test scenarios. Implemented interfaces, limits and features are defined by each project’s scope.