Serverless and Observer pattern ( ¿It is possible to listen to events from a lambda? )

I was thinking about serverless architecture and the observer pattern (i think that it does not fit into serverless).

How can I implement the Observer design pattern usings a lambda or similar things (severless architecture)?.

My use case is:

1. Listen to events from ethereum blockchain usings ethers.js or web3.js. I am doing this from an aws lambda function. The lambda is activated on a scheduled time base event.

2. Sending some of the recollected data in the previous step to an aws RabbitMQ

¿In this kind of technological stack (lambdas, managed services and so) It is mandatory to listen to from a 100% live application (always on)?

I can't imagine a lambda function implementing this pattern, but...ideas are welcome!

Thanks in advance