Amazon EC2 is our primary application hosting solution. Most applications are not exposed on the internet and use a virtually private cloud to interact with each other.
While we experimented with Cassandra in the past, we are no longer using it. It is, however, open for consideration in future projects.
Docker containers are deployed on top of Mesos using Marathon to isolate failure and ensure portability.
Mesosphere is used for Orchestration of Microservices for the applications which run all the business logic.