This topic answers frequently asked questions about using the ApsaraMQ for MQTT console.
Why can't I delete an MQTT instance?
You must delete all resources in an MQTT instance, such as topics and groups, before you can delete the instance.
Why can't I find message traces when I query by Group ID and Device ID?
If a client ID contains invalid characters, the message trace query fails. Check if the client ID contains any special characters and ensure that it complies with the naming conventions. For more information about the naming conventions, see Limits.
Why is my MQTT instance still being billed when it is not visible in the console?
The ApsaraMQ for MQTT service depends on ApsaraMQ for RocketMQ. If your account has an overdue payment, the ApsaraMQ for RocketMQ service is automatically shut down. This causes the MQTT instance to become invisible in the console, but the MQTT service is still running.
Even after you clear the overdue payment, the ApsaraMQ for RocketMQ service is not automatically re-enabled. As a result, the MQTT instance remains invisible in the console. To view the MQTT instance in the console, you must manually re-enable the ApsaraMQ for RocketMQ service.
Why can't I see my MQTT instance even after I enabled ApsaraMQ for RocketMQ?
After you enable the ApsaraMQ for RocketMQ service for the first time, you must wait about 10 minutes for the instance list to appear in the ApsaraMQ for MQTT console.
Where do I configure threshold alerts for an MQTT instance?
You can configure alerts in the upper-right corner of the instance details page in the ApsaraMQ for MQTT console.
What is the maximum time range in which CloudMonitor can query metrics?
Cloud Monitor for ApsaraMQ for MQTT supports querying metric data from the last three days.
Why does the device remain connected in the console after the device is power off?
ApsaraMQ for MQTT periodically checks client heartbeats. The system disconnects a client if it detects no heartbeat for a duration of 1.5 × the keepalive time.
For example, if the default keepalive time is 90 seconds, the system disconnects after 135 seconds. Heartbeat detection is not a real-time detection capability, a longer period of time than 135 seconds may be required for the system to detect that the heartbeat timed out. In this case, the system also requires a longer period of time to disconnect.
How do I modify subscriptions in the console?
Subscriptions are specified in the SDK code that is used to subscribe to messages and can only be queried in the console.
Why am I unable to query the consumption traces of offline messages in the console?
If the offline messages feature is not configured, the broker does not push messages when the client is disconnected and cannot receive messages that are produced during disconnection when the client reconnects.
If the offline messages feature is required, set the cleanSession parameter to false and the QoS parameter to 1. For more information, see Combinations of QoS and cleanSession
Why am I unable to consume some messages if the message traces in the console indicate that the messages are sent?
Possible cause: When the broker pushes messages, the client is disconnected and the offline messages feature is not configured. In this case, you cannot consume the messages that are produced during disconnection.