The goal of securing a cloud computing system involves both protecting the instances, data on the instances, and ensuring users are authenticated for actions and that borders are understood by the users and the system. Protecting the system from intrusion or attack involves authentication, network protections, and compromise detection.
Authentication - Each instance is authenticated with a key pair.
Network - Instances can communicate with each other but you can configure the boundaries through firewall configuration.
Monitoring - Log all API commands and audit those logs.
Encryption - Data transfer between instances is not encrypted.