[PaulRobinson]

There are multiple alternatives to running your own DB service, and again, all pay-per-use.

In the original article the author suggested on a successful subscription a write to the MailChimp API (because that's the product). In that example, MailChimp is the DB. You don't have to run a copy of a DB locally if you architect things like that. Obviously if the call fails, you need to think about what you fall back to, which is why error handling is such a critical piece of the the Lambda ecosystem - as it should be for every ecosystem, really.

[lsaferite]

In this case you should really just dump the subscription on a queue (SQS) and process the payment to mailchimp on a different thread that can deal with errors.