Notifying a publisher of life-cycle events for topic subscription

A method, comprising:

• performing, by one or more computing devices that implement a message broker of a publish-subscribe messaging system:
• for a given topic that a publisher is assigned to publish messages on:
• detecting a transition in a number of subscribers to the topic from zero to one or more or from one or more to zero;
• receiving, by the message broker from the publisher via an application programming interface (API), a request for an indication of whether there are any subscribers to the topic;
• and
• in response to the request, sending, from the message broker to the publisher via the API, the indication of whether there are any subscribers to the topic, wherein the indication sent from the message broker to the publisher via the API is based on the detection by the message broker of the transition in the number of subscribers to the topic.

One or more non-transitory computer-accessible storage media storing program instructions that when executed on or across one or more processors cause the one or more processors to implement a message broker of a publish-subscribe messaging system to:

• for a given topic that a publisher is assigned to publish messages on:
• detect a transition in a number of subscribers to the topic from zero to one or more or from one or more to zero;
• receive, by the message broker from the publisher via an application programming interface (API), a request for an indication of whether there are any subscribers to the topic;
• and
• in response to the request, send, from the message broker to the publisher via the API, the indication of whether there are any subscribers to the topic, wherein the indication sent from the message broker to the publisher via the API is based on the detection by the message broker of the transition in the number of subscribers to the topic.