[QUESTION]How JETLINKS maintains the connection status of the device about jetlinks-community HOT 3 CLOSED

1. Device real status will managed by DeviceSessionManager in memory.
2. When device register to DeviceSessionManager, device state,server id will save to DeviceRegistry(Redis).
3. Publish DeviceOnlineMessage to EventBus /device/{productId}/{deviceId}/online.
4. DeviceMessageBusinessHandler subscribe topic /device/*/*/online,offline from EventBus when server started.
5. Synchronization device real state to PostgreSQL when EventBus sent /device/*/*/online,offline message ,( get state from DeviceRegsitry )
6. Check real state when api request: /device/instance/{deviceId}/detail and synchronization it.

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2. When device register to DeviceSessionManager, device state,server id will save to DeviceRegistry(Redis).

In fact, Redis can not keep real-time for device state:
e.g. When the service restarts or crashes, the state does not have time to synchronize.

JetLinks device state check strategy :

1. Get server id info in DeviceRegistry (store in redis, cache in memory.).
2. RPC the server id: Get device real state.
3. If cached state not equals RPC response, synchronization to PostgreSQL

TIP: The same principle was used in a send device message (when cluster).

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1. Device real status will managed by DeviceSessionManager in memory.
2. When device register to DeviceSessionManager, device state,server id will save to DeviceRegistry(Redis).
3. Publish DeviceOnlineMessage to EventBus /device/{productId}/{deviceId}/online.
4. DeviceMessageBusinessHandler subscribe topic /device/*/*/online,offline from EventBus when server started.
5. Synchronization device real state to PostgreSQL when EventBus sent /device/*/*/online,offline message ,( get state from DeviceRegsitry )
6. Check real state when api request: /device/instance/{deviceId}/detail and synchronization it.

Thank you for your answer, but I still have a question:

Is it not quite appropriate to store the real state of the device in memory? This is not conducive to horizontal scaling. Perhaps it would be better to use Redis' ZSET to store the device ID and use the device's last active time as its score?

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