Answers to common questions about managing instances, tracing messages, monitoring metrics, and troubleshooting device connections in the ApsaraMQ for MQTT console.
Instance management
Why can't I delete an MQTT instance?
Delete all resources in the instance first, including topics and groups. The console blocks deletion until the instance contains no resources.
Why is my MQTT instance invisible in the console but still being billed?
ApsaraMQ for MQTT depends on ApsaraMQ for RocketMQ. If your account has an overdue payment, the ApsaraMQ for RocketMQ service shuts down automatically, which hides the MQTT instance from the console. The MQTT service itself continues running and accruing charges.
Clearing the overdue payment does not re-enable ApsaraMQ for RocketMQ automatically. Manually re-enable the ApsaraMQ for RocketMQ service to make the MQTT instance visible again.
Why can't I see my MQTT instance after enabling ApsaraMQ for RocketMQ?
If you enabled ApsaraMQ for RocketMQ for the first time, wait about 10 minutes. The instance list takes a few minutes to populate in the ApsaraMQ for MQTT console.
Message tracing
Why does a message trace query by Group ID and Device ID return no results?
This typically means the client ID contains invalid characters. Check the client ID for special characters and verify that it follows the naming conventions.
Why can't I find consumption traces for offline messages?
The offline message feature is not configured. Without it, the broker does not store messages for disconnected clients, so there are no consumption traces to query.
To enable offline messages, set cleanSession to false and QoS to 1 in your SDK code. For details on how these parameters interact, see Combinations of QoS and cleanSession.
Why do message traces show messages as sent, but the client never received them?
This happens when the broker pushes a message while the client is disconnected and the offline message feature is not configured. The broker delivered the message, but no client was online to receive it, and the message was not stored for later delivery.
To prevent this, enable offline messages by setting cleanSession to false and QoS to 1.
Monitoring and alerts
Where do I configure threshold alerts for an MQTT instance?
On the instance details page in the ApsaraMQ for MQTT console, click the alert configuration option in the upper-right corner.
What is the maximum time range for CloudMonitor metric queries?
CloudMonitor retains metric data for the last three days. Metrics older than three days cannot be queried.
Device connections
Why does a device still show as connected after it is powered off?
ApsaraMQ for MQTT detects disconnects through periodic heartbeat checks, not in real time. The system waits 1.5 times the keepalive interval before marking a client as disconnected.
With the default keepalive of 90 seconds, the theoretical disconnect delay is 135 seconds. In practice, it can take longer because heartbeat detection runs on a periodic cycle rather than continuously.
Subscriptions
How do I modify subscriptions in the console?
Subscriptions cannot be modified in the console. Subscriptions are defined in your SDK code when subscribing to messages. The console only displays existing subscriptions as a read-only view.