Explanation
A synthetic full backup is a type of backup that combines the latest full backup with all the subsequent incremental backups to create a new full backup. This type of backup will back up all the data from each VM daily while also saving space, as it does not require a new full backup every time and only transfers the changed data from the incremental backups. Reference: [CompTIA Cloud+ Certification Exam Objectives], Domain 3.0 Maintenance, Objective 3.2 Given a scenario, implement backup, restore, disaster recovery and business continuity measures.

The correct answer is C and D.
C) Fix the file permissions with read-only access to the owner of the file.
D) Open port 22 access for the computer's public IP address.
The authorized_keys file on the server should have read-only access for the owner of the file, and no access for anyone else. This ensures that only the owner can read the public keys that are authorized to log in, and no one can modify or delete them. The file permissions can be fixed with the command chmod 400 ~/.ssh/authorized_keys on the server. This is a recommended security practice for SSH key-based authentication123.
The computer that wants to log in to the server using SSH key-based authentication needs to have access to port 22 on the server, which is the default port for SSH service. This can be done by opening port 22 access for the computer's public IP address on the server's firewall or security group settings. This allows the computer to initiate an SSH connection to the server and authenticate with its private key. Opening port 21, which is used for FTP service, is not relevant or secure for SSH key-based authentication1.

Reference: https://docs.microsoft.com/en-us/azure/key-vault/key-vault-whatis Key Vault is a service that allows you to store and manage secrets and keys for your cloud services in a secure and centralized way. It also provides access control, auditing, and encryption features. This would be the best option to automate the management of secrets and keys for all cloud services with minimal effort and low cost.
Reference: CompTIA Cloud+ Certification Exam Objectives, Domain 3.0 Maintenance, Objective 3.4 Given a scenario, implement automation and orchestration to optimize cloud operations.

A virtual extensible local area network (VXLAN) is a type of network virtualization technology that creates logical networks or segments that span across multiple physical networks or locations. Moving the web and database servers onto the same VXLAN can help resolve the network throughput issues following a deployment, as it can reduce the network traffic between the database and the web servers by using a common virtual network identifier (VNI) and encapsulating the traffic within UDP packets. Moving the web and database servers onto the same VXLAN can also improve performance and security, as it can provide higher scalability, isolation, and encryption for the network traffic. References: CompTIA Cloud+ Certification Exam Objectives, page 15, section 2.8