Application installed node state change notifiers are called when a remote node transitions from active to unavailable and from unavailable to active. The In Up Notifier and In Down Notifier states defined in Table 6.1, “Remote node states” are seen when a node notifier is being called.

When a node state change notifier is installed, it is guaranteed to be called for all active remote nodes already discovered by the local node. Node notifier execution is serialized for a specific remote node. A call to a notifier must complete before another notifier is called. For example, if a remote node becomes unavailable while an active notifier is being executed, the unavailable notifier is not called until the active notifier completes.

Node state change notifiers are called in a transaction.