Azure Key Vault is a cloud service provided by Microsoft Azure that allows users to securely store and manage sensitive information such as encryption keys, secrets, and certificates. It is designed to safeguard cryptographic keys and other secrets used by cloud applications and services. Azure Key Vault helps ensure that data at rest is protected by providing secure storage for encryption keys, which can be used to encrypt data stored in Azure services. It also supports key management tasks such as creating, importing, rotating, and controlling access to keys, making it an essential tool for managing data security in the cloud.

Placing the web server in a separate Demilitarized Zone (DMZ) behind the firewall is a security best practice that allows an organization to isolate its public-facing services from the internal network. This setup ensures that if the web server is compromised, the attacker would not have direct access to the internal network resources. Additionally, the DMZ provides a controlled environment where network traffic to and from the web server can be monitored effectively, facilitating the detection of any future attacks. The firewall serves as a barrier, with specific rules that only allow necessary communication to and from the DMZ, thereby enhancing the overall security posture of the organization.

The deployment mode that allows an Intrusion Detection System (IDS) or Intrusion Detection and Prevention System (IDPS) to both detect and stop malicious traffic is known as inline mode. In this mode, the IDS/IDPS is placed directly in the network's traffic flow. All traffic must pass through the system, allowing it to inspect packets in real-time and take immediate action to block potential threats before they reach their destination. This contrasts with promiscuous or passive modes, where the system only monitors and alerts on traffic without the ability to intervene directly.