Triggering Lambda when a device Shadow updates

Question

I've set up a rule

SELECT * FROM '$aws/things/+/shadow/update/accepted'

This rule triggers my lambda function when the shadow of any thing in my AWS IoT updates.

Instead I want it to get triggered only when the shadows of some things are updated, not all of them. Any way I can do that?

Answer 1

I recently learned that you can use functions to filter on parts of the topic, and something like this could potentially work for you:

SELECT *
FROM '$aws/things/+/shadow/update/accepted'
WHERE startswith(topic(3), 'someprefix-')

This would only trigger the action(s) when the part of the topic captured by the + started with "someprefix-". You can use other functions to filter in other ways if a prefix does not work for you.