Synchronizing Replica Caches
The Orchestrator activates a Replica cache when it has successfully synchronized the state of the cache with the Master cache. A Master cache can be immediately activated by an Orchestrator, as there is no synchronization to perform. Orchestrators managing Master caches perform continuous health-checking to verify the active status of the Replica caches managed by the other Orchestrators.
There are two main cases when the state of a Replica cache needs to be resynchronized by the Master cache: bootstrapping a new cache and recovering after a failure.
Bootstrapping a new cache
Perform these steps when starting a cache for the first time, or after the cache was fully cleared.
1. Ensure the Replica cache configuration is the same as the Master cache.
2. Ensure the WAN configuration for the Replica cache is valid:
Check that there is a valid list of Master caches.
For a given cache, the WAN configuration should be identical across all regions.
3. Ensure the TSA is running.
4. Start the Orchestrator.
On startup, the new Replica cache will be inactive while synchronizing (clients cannot use the cache). In this mode, it is receiving incremental updates and synchronizing the full state of the cache. Once fully synchronized, the Replica cache will be active.
Recovering after failure
BigMemory WAN Replication is built with fault tolerance features to automatically handle short-term failures and most longer-term failures.
When a replica reconnects with the master, its behavior is governed by the Orchestrator configuration parameter replicaDisconnectBehavior. If this parameter is set to:
remainDisconnected, the replica will remain disconnected from the master, and will continue to operate offline.
reconnectResync, the replica will reconnect to the master and will resync the contents of its cache. In this case, all local changes on the replica region will be dropped in favor of whatever is in the master region.