EdgeHub awaits for Twin in non-MQTT broker scenario (#4084) #4129
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TL;DR Currently the protocol head could start up before the route configuration is setup on edgeHub. This causes the messages which are sent before the route is config to be permanently lost. Background: Historically, the edgeHub tries to download its twin to get the routings before it starts up the protocol heads, then it was waiting till the twin arrived, then it had the routings, then it started the protocol heads. With the new broker and nested scenario, the problem is that it needs the protocol heads up to get the twin. The twin comes through the MQTT broker, and one of the protocol heads handle the messages from the broker. The problem arises because protocol heads are up, but no twin available yet. Fix: If the upstream is not via MQTT broker, then await the twin task; otherwise, let it runs. Todo: This code change does not handle the scenario: IoTHub <--MQTT/BRIDGE-- EdgeDevice <--AMQP-- DeviceA Since we are not waiting on the configUpdate (that would be a dead lock, because configUpdate() needs the new mqtt/broker to be started), the code goes ahead and starts every protocol head i.e. AMQP listener for connecting clients. This can cause an AMQP message to be sent (into the void) before a route is setup on the DeviceA.
vipeller
approved these changes
Dec 18, 2020
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TL;DR (cherry-picked: 40acc96)
Currently the protocol head could start up before the route configuration is setup on edgeHub. This causes the messages which are sent before the route is config to be permanently lost.
Background:
Historically, the edgeHub tries to download its twin to get the routings before it starts up the protocol heads, then it was waiting till the twin arrived, then it had the routings, then it started the protocol heads. With the new broker and nested scenario, the problem is that it needs the protocol heads up to get the twin. The twin comes through the MQTT broker, and one of the protocol heads handle the messages from the broker. The problem arises because protocol heads are up, but no twin available yet.
Fix:
If the upstream is not via MQTT broker, then await the twin task; otherwise, let it runs.
Todo:
This code change does not handle the scenario:
IoTHub <--MQTT/BRIDGE-- EdgeDevice <--AMQP-- DeviceA
Since we are not waiting on the configUpdate (that would be a dead lock, because configUpdate() needs the new mqtt/broker to be started), the code goes ahead and starts every protocol head i.e. AMQP listener for connecting clients. This can cause an AMQP message to be sent (into the void) before a route is setup on the DeviceA.