Integration / Apache Pulsar Interview questions
When should you use Failover subscription instead of Exclusive?
Use Failover when you want the strict single-active-consumer ordering guarantee of Exclusive, but also want automatic, fast promotion of a backup consumer if the active one disconnects, without the application having to detect and reconnect manually.
With Failover, multiple consumers can register on the subscription, but only the one with the highest priority (or earliest registration, on a tie) is actively receiving messages; the rest sit as hot standbys ready to take over instantly on disconnect.
Exclusive, by contrast, simply refuses a second consumer outright, which is fine for a single-instance application but provides no built-in redundancy if that one instance goes down.
Failover differs from Exclusive mainly by allowing:
With Exclusive, a second consumer attaching to the same subscription is:
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