This entry would attempt to shed some light on the various standby modes:
- Cold Standby: when another entity (process, data center etc.) takes over when the first entity is not available. The second entity requires a boot time to take over and is not seamless to the consumers.
- Hot Standby: when another entity can take over seamlessly for the first entity in the event of the first one going down. The data has been replicated, all the updates are available to the second entity.
- Active – Active: When both the entities are live concurrently. This is the most complicated to setup and debug. Conflicts have to be managed between the two or more entities, there may be network issues between the entities and so on – these issues lend a whole lot of complexity in the design and implementation of the system. Decisions have to be made on reaching the right consistency and availability balance.