End-to-end user login process in Azure Virtual Desktop (AVD)

Fig: End-to-end login process in Azure Virtual Desktop.

In any AVD interview, one of the most common questions is to describe the end-to-end sign process of a user in Azure Virtual Desktop. Today I am going to show you this login process in detail.

Let’s see how it works.

When a user logs in to an Azure Virtual Desktop (AVD) from a Microsoft Remote Desktop Client (RDC) on Windows, several backend processes occur to establish the connection and provide the user with a remote desktop session. Here’s a high-level overview of what happens:

      Authentication and Authorization

• User Credentials: When users enter user credentials (username and password) in the Remote Desktop Client, they are sent securely to Azure Active Directory (Azure AD) for authentication.
• Multi-Factor Authentication (MFA): If MFA is enabled, an additional verification step (e.g., a code from the Microsoft Authenticator app) is required.
• Entra ID Validation: Entra ID validates user credentials and checks if users have the necessary permissions to access the Azure Virtual Desktop resources.
• Role-Based Access Control (RBAC): Azure checks if the user account has the appropriate RBAC roles assigned (e.g., Virtual Machine User Login) to access the AVD session.
  
  Broker Service Interaction

• Azure Virtual Desktop Broker Service: Once authenticated, the Remote Desktop Client communicates with the AVD Broker Service, which acts as the intermediary between the client and the virtual desktop session.
• Session Allocation: The Broker Service checks for available session hosts (virtual machines) in the AVD host pool and assigns user to an appropriate session host. If a user has an existing session, it reconnects user to that session.
• Load Balancing: If multiple session hosts are available, the Broker Service uses load-balancing algorithms to distribute sessions evenly across hosts.
  
  Connection to the Session Host

• Remote Desktop Protocol (RDP): The Broker Service provides the client with the necessary connection details (e.g., session host IP address, port) to establish an RDP connection.
• Secure Connection: The RDP connection is encrypted using TLS (Transport Layer Security) to ensure secure communication between the client and the session host.
• Gateway Service: If the session host is behind a firewall or in a private network, the AVD Gateway Service facilitates the connection by acting as a relay between the client and the session host.
  
  Session Initialization

• User Profile and Settings: The session host retrieves the user profile and settings from FSLogix (if configured) or a network share. This ensures a consistent experience across sessions.
• Application Launch: The session host launches the desktop or applications assigned to the user based on the user AVD configuration.
• Session State: If users are reconnecting to an existing session, the session host restores the session to its previous state.
  
  Ongoing Communication

• Input/Output Redirection: The Remote Desktop Client sends userr keyboard, mouse, and other input data to the session host, and the session host sends display output, audio, and other data back to the client.
• Monitoring and Management: The AVD infrastructure continuously monitors the session for performance, health, and security. If issues are detected, the Broker Service may redirect the user to another session host.
  
  Logging and Auditing

• Activity Logs: Azure logs all login attempts, session starts, and other activities in Azure Monitor and Azure AD logs for auditing and troubleshooting purposes.
• Diagnostics: If enabled, diagnostic data is collected to help administrators monitor and optimize the AVD environment.

Key components involved:

• Entra ID: Handles authentication and user management.
• AVD Broker Service: Manages session allocation and load balancing.
• AVD Gateway Service: Facilitates secure connections to session hosts.
• Session Hosts: Virtual machines running desktops or applications.
• FSLogix: Manages user-profiles and settings (optional but commonly used).
• Remote Desktop Protocol (RDP): The protocol used for remote desktop communication.

This entire process is designed to be seamless, secure, and scalable, providing users with a reliable remote desktop experience while ensuring compliance and performance.