I'm in agreement with mpdehaan2 here.

By sticking with a single cloud provider you get a lot of benefits. One of the more major benefits is cost, as you can do things like reserved instance in EC2. Another major benefit of sticking with a single provider is that you get to use solutions that only that provider has, which in this case is KMS, DynamoDB and IAM.

The biggest downside of being cloud agnostic is that you're stuck with the smallest combination of features that all of the clouds provide.