A. Deploy the application to a staging environment and force a failover to this environment. To restore the previous version, create a backup and restore from the previous night's backup.

B. Use a rolling deployment to update all the servers in the PROD cloud environment with the new application. To switch to the previous version, repeat the process.

C. Deploy the application to the PROD cloud environment and the previous version to QA. To switch to the previous version, promote the QA environment to PROD.

D. Deploy the application to a subset of servers in the environment and route traffic to these servers. To switch to the previous version, change the route to the non-updated servers.