You can use the request-reply model for applications that publish or deliver a request event to a server application which is expected to return a reply event. The reply event can contain data or can simply be an acknowledgment with no data.

A tag envelope field is set by the BrokerClusterPublisher internally to identify the request event that it is sending. When a server application receives the request event and prepares the reply event, it ensures that the same tag field is set for the reply as was received on the request event. If your requestor sends several different request events, it should set each with a different tag field. When your requestor receives a reply event, it can check the tag field to determine the original request with which the reply is associated. BrokerEvent.getTag and BrokerEvent.setTag methods are used to get and set tag field values from an event.