Bastion

BastionLast Updated:  6th March 2025

Azure Bastion: Secure and Seamless RDP/SSH Access to Your Virtual Machines

Technical Overview

Imagine this: your organisation has deployed a fleet of virtual machines (VMs) in Azure, hosting critical applications and sensitive data. The challenge? Ensuring secure, seamless access for administrators without exposing these VMs to the public internet. This is where Azure Bastion steps in, offering a fully managed platform for secure RDP and SSH connectivity directly through the Azure portal.

Azure Bastion eliminates the need for public IP addresses on your VMs, reducing the attack surface and mitigating risks associated with brute force attacks. It operates as a Platform-as-a-Service (PaaS) solution, seamlessly integrating with your Azure Virtual Network (VNet). By leveraging Bastion, administrators can connect to their VMs using their browser, without the need for additional client software or VPNs.

Architecture

At its core, Azure Bastion is deployed within a VNet as a dedicated subnet called the AzureBastionSubnet. This subnet requires a minimum prefix of /27 to accommodate the service. Once deployed, Bastion establishes a secure connection between the Azure portal and the target VM over RDP or SSH, using Transport Layer Security (TLS) to encrypt the session.

The architecture is designed to be highly scalable and resilient. Bastion instances are automatically patched and updated by Microsoft, ensuring you always have the latest security features without manual intervention. Additionally, it supports integration with Azure Active Directory (Entra ID) for centralised identity management and role-based access control (RBAC).

Scalability

Azure Bastion is built to scale with your workloads. Whether you have a single VM or hundreds spread across multiple VNets, Bastion can handle the load. For large-scale deployments, you can leverage the VNet peering feature to enable Bastion access across peered VNets, eliminating the need to deploy multiple instances of Bastion.

Data Processing

Azure Bastion does not store or process your data. It acts as a secure gateway, facilitating encrypted communication between your browser and the VM. This ensures compliance with data sovereignty and privacy regulations, as no session data is retained by the service.

Integration Patterns

Azure Bastion integrates seamlessly with other Azure services to enhance security and operational efficiency:

  • Network Security Groups (NSGs): You can apply NSGs to the AzureBastionSubnet to control inbound and outbound traffic, further tightening security.
  • Azure Policy: Use policies to enforce the deployment of Bastion for all VNets, ensuring consistent security practices across your organisation.
  • Azure Monitor: Track Bastion usage and performance metrics to optimise your deployment.

Advanced Use Cases

Beyond basic RDP/SSH access, Azure Bastion supports advanced scenarios:

  • Custom Ports: Configure Bastion to use non-standard ports for RDP and SSH, enhancing security by obscurity.
  • Native Client Support: Connect to VMs using native RDP/SSH clients instead of the Azure portal, providing flexibility for administrators.
  • Azure Bastion Standard SKU: This SKU offers additional features like forced tunnelling, increased session limits, and support for multiple IP addresses.

Business Relevance

In today’s threat landscape, securing administrative access to cloud resources is non-negotiable. Azure Bastion addresses this need by providing a secure, scalable, and user-friendly solution for VM management. Here’s why it matters:

  • Reduced Attack Surface: By eliminating the need for public IPs, Bastion significantly lowers the risk of external attacks.
  • Operational Efficiency: Administrators can access VMs directly through the Azure portal, streamlining workflows and reducing reliance on VPNs or third-party tools.
  • Cost-Effective: With no additional software or hardware requirements, Bastion offers a cost-effective alternative to traditional remote access solutions.

For organisations prioritising compliance, Bastion ensures secure access without compromising on regulatory requirements. Its integration with Entra ID further strengthens identity management, enabling granular access control and auditability.

Best Practices

To maximise the benefits of Azure Bastion, consider the following best practices:

  • Subnet Configuration: Always use a dedicated subnet with the recommended /27 prefix for Bastion. Avoid deploying other resources in this subnet.
  • NSG Rules: Apply restrictive NSG rules to the AzureBastionSubnet, allowing only required traffic.
  • Enforce RBAC: Use Entra ID to assign roles and permissions, ensuring only authorised users can access Bastion.
  • Monitor Usage: Leverage Azure Monitor and Log Analytics to track Bastion usage and identify potential anomalies.
  • Standard SKU: For enterprise deployments, consider upgrading to the Standard SKU for enhanced features and scalability.

Relevant Industries

Azure Bastion is a versatile solution applicable across various industries:

  • Financial Services: Securely manage VMs hosting sensitive financial data, ensuring compliance with regulatory standards.
  • Healthcare: Provide secure access to VMs containing patient records or medical applications, safeguarding sensitive information.
  • Retail: Enable secure management of VMs running e-commerce platforms or inventory systems.
  • Government: Ensure secure access to critical infrastructure while meeting stringent security and compliance requirements.
  • Education: Facilitate secure remote access for IT administrators managing campus-wide systems.

Adoption Insights

With an adoption rate of 42.31%, Azure Bastion is steadily gaining traction among organisations seeking secure and efficient VM management solutions. This presents an opportunity for businesses to get ahead of the curve by implementing Bastion and enhancing their security posture.

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