IoT Events: Publish IoT Topic action with dynamic topic name

Question

I'd like to be able to publish a message to a topic, which name is build up dynamically based on one of the input values.
I can access to the input already when setting up Transition Events, but can't find a way to interpolate the input value into the topic name.

Suppose I have an input such as: $input.foo = bar
Would like to use it in the topic name as: "my/topic/$input.foo", resulting into "my/topic/bar"

Have tried all type of proposed substitution templates w/o success (https://docs.aws.amazon.com/iotevents/latest/developerguide/iotevents-expressions.html)

Answer

Answering to my own question, after some further testing. I did not manage to interpolate the topic dynamically on-the-fly as I wanted. Instead, I found a workaround by declaring a variable that contains the resolved interpolation in a previous state. For instance, the variable **leds_topic** is initialized with **'gate/' + $input.gate_sensors.gateid + '/leds'**
Aterwards, I can publish to that topic using as Topic name **($variable.leds_topic)**

IoT Events: Publish IoT Topic action with dynamic topic name

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