Subscriptions: Multiple Groups of Consumers on a Pulsar Topic

Apache Pulsar supports multiple groups of consumers on a topic, allowing multiple applications to consume messages from a single topic simultaneously. This is achieved through subscriptions, which manage consumers on topics and keep track of the position in the topic from which each consumer reads. A Pulsar topic can support many subscriptions at the same time, enabling message fan-out to multiple applications. Apache Pulsar offers four different types of subscriptions: exclusive, failover, shared, and key_shared. These subscriptions vary based on how messages are sent to consumers within that subscription. By using these subscriptions, developers can implement various patterns such as competing consumers or active-standby configurations.