Understanding failure recovery

When a publisher exits, the subscriber receives a "no more publishers" message for the topic. There is no need to unsubscribe or resubscribe. If a new publisher appears and starts to publish to the same topic, the subscriber automatically starts receiving updates.

If the connected PubSub Engine shuts down, or if a subscriber closes or loses its connection to the PubSub Engine, the engine stops tracking the subscriber’s subscriptions.

If the subscriber uses the PubSub Data Access Layer (DAL) Application Programming Interface (API), then the reconnection and re-subscriptions are handled automatically.

If a subscriber is implemented using a legacy PubSub API (that is, one other than PubSub DAL), it must reconnect to the PubSub Engine and resubscribe for itself.