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This article is to explain how to generate an “expired” message and how to catch it in the $expired/# topic.

\uD83D\uDCD8 Instructions

1. Prepare a HiveMQ broker with a TCP listener on localhost:1883.

2. On the broker, enable Expired Messages Topic add-on.
   Enabling Expired Messages Topic add-on has 2 workings:

   1. The Expired Messages Topic add-on prefaces the topic of expired messages with $expired/.
      So, if a message published to my/topic/test is expired, it will be published to topic $expired/my/topic/test.

   2. The Expired Messages Topic add-on exposes additional metrics in the HiveMQ standard metrics:

      • com.hivemq.messages.expired-messages

      • com.hivemq.messages.expired.topic.expired.count

        and other metrics.

Following steps explain how to create a situation when a message is expired.

...

1. is published to the topic $expired/test and received by the sub-expired client.

2. metrics updated
   com.hivemq.messages.expired-messages
   com.hivemq.messages.expired.topic.expired.count