IoT Edge module routing

Question

Is it possible to route an output of an edge module into the input of the very same module (loop a message into the same module)?

Answer 1

Let's do an experiment.

I created this VM running iot edge. I added the svelde/iot-edge-echo:2.0.1-amd64 module with an input and an output (what is coming in, is also send out):

I added this route:

FROM /messages/modules/echo/outputs/output1 INTO BrokeredEndpoint("/modules/echo/inputs/input1")

So the outcoming echo module messages go into the echo module.

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Now I only have to send one message to the echo module. We do this with the svelde/iot-edge-one-message:0.0.1-amd64 module.

This 'one' module sends one message to 'output1' on restart of the module.

So I added to modules, the 'one' module and the 'echo' module and this extra route:

FROM /messages/modules/one/outputs/output1 INTO BrokeredEndpoint("/modules/echo/inputs/input1")

I now restart the 'one module'.

The message is sent after the restart.

The message arrives at the echo module:

But I see no actual resend of the same message over and over. So it seems the routing is limited to only other modules.

To prove this, I added a second echo module.

So the routing goes:

FROM /messages/modules/one/outputs/output1 INTO BrokeredEndpoint("/modules/echo/inputs/input1")
FROM /messages/modules/echo/outputs/output1 INTO BrokeredEndpoint("/modules/echo2/inputs/input1")
FROM /messages/modules/echo2/outputs/output1 INTO BrokeredEndpoint("/modules/echo/inputs/input1")

This time we see the infinite loop:

Conclusion: Routing is protected against sending a message to itself. But you can fool it by putting a (the same) module in between.