MongoDB backup strategy for AWS
Old question but I think that I can contribute with more details and informations about a real success case.
In a production environment I have 3 Mongodb with replicaset running in 3 T2.micro instances, 1 instance is the primary, 1 instance is the secondary and 1 instance is delayed (every 4 hours is synchronized) with persistent EBS (it's not deleted after instance reboot).Every 4.5 hours I start a Lambda process that makes a EBS snapshot of delayed instance and sends to a S3 bucket.This is working pretty well.
Some links that can help:
Who better than 10gen (MongoDB developers) to responds you.
You can see in follogin site, official documentation about MongoDB backups in EC2 instances. http://docs.mongodb.org/ecosystem/platforms/amazon-ec2/
They suggest an EBS snapshots. This solution permits start instance in a few of seconds with a "photo" of your database.
We use (at least two) linux instances with the data stored on EBS and replica sets (http://www.mongodb.org/display/DOCS/Replica+Sets).