Is there a hard limit on number of rules on an event bus?

Hi,

You should not have an individual rule for each different MQTT connection. You should rather have a single rule for all connections triggering 1 single Lambda. This Lambda will then use a lookup table (redis cache or DDB table) to match the connection to a user and then be able to route the MQTT messages to the user.

Parallelism will be managed for you by Lambda runtime: you'll get a new independent instance of your function for each incoming message.

Best,

Didier

Personally, Im not sure of the answer but It sounds like eventbridge is the wrong product for what your trying to achieve because creating an event bridge rule for every user just doesnt seem to scale to me and will be unmanageable. I would re-evaluate the method and what your trying to achieve.

I would only use eventbridge for routing events between services and not down to a low level such as users.

How about using permissions in MQTT where your devices can only subscribe to their own topic and then your application can publish to which ever topic you need to send to users? Route messages say to a lambda function and it will publish to the correct Topic?