A defence in depth security policy should be applied to cloud architecture in order to secure it.
At the application level proper SDLC should be followed, using a web application firewall is a good option. At the information level using encryption, Key management and access control list will protect the data. At the management level, proper patch management, configuration management and monitoring have to be done. Deploying multiple defences at various layers of the cloud will provide us with a secure cloud.