AWS Lambda functions are a great way to run some code on a trigger/schedule without needing a whole server dedicated to it. They can be cost effective, but be careful depending on how long they run, and the number of executions per hour, they can be quite costly as well.
Cross Region MongoDB Across A Slow Network (Napster) Bad, AWS Snapshots (Metallica) Good! I recently found myself in a bit of a pickle. My team and I had deployed a 3 node MongoDB cluster configured as two nodes in us-east-1 and one node in us-west-2 to maximize our availability while minimizing cost.