Personally, I’d never choose aws lambda.

A serverless approach doesn’t seem to leverage any of the strong points of BEAM, and waiting the startup time of BEAM on such environment is not worth it. So if you’re going serverless, most probably you’re not using elixir.

Oban on the other side can handle running multiple instances of the same service, even if you don’t run your elixir app as a beam cluster.

Just because of that, if your codebase is mainly in elixir, i don’t see any good reasons to use aws lambda.
If you’re dealing with multiple languages or elixir is not your main language, there might be reasons to consider using aws lambda.

edit: and it’s good to keep in mind that oban is not the only way to do background work in elixir. it’s a good one, but there stuff you can handle easily with supervised tasks and other approaches.

I can surely see the “cost” factor, but to me it just sounds ludacris to regularly ping a service so it doesn’t shut down, when the platform of the service is built to reduce cost by shutting down services when not used – over say a server running full time. So much complexity when one could just use a server, which doesn’t shut down the service in the first place.

Big thing for me is simplicity. One thing I love with elixir is that you can have pretty much everything in your app + PostgreSQL. I use to be much more into microservices and stuff but in the end you just end up spending so much on connecting everything and development becomes so much more complex.