Bastion

A bastion, also known as a bastion host, is a specially secured server that acts as the single, controlled entry point into a private network. Instead of exposing internal systems directly to the internet, administrators connect to the bastion first and then access internal resources from there. This design greatly improves security and visibility.

What Problem a Bastion Solves

In many environments, servers, databases, and services should never be directly accessible from the internet. However, administrators still need a way to manage them.

Without a bastion:

• Multiple servers may be exposed to the public internet
• Each system needs its own security rules
• Tracking and auditing access becomes difficult

A bastion solves this by concentrating access through one tightly locked and monitored system.

How a Bastion Works

A bastion is typically placed in a public facing network segment, such as a DMZ or public subnet. It has very limited functionality and is hardened to reduce risk.

The usual access flow looks like this:

1. An administrator connects to the bastion using SSH or RDP
2. Authentication and authorization are verified
3. Access is logged and monitored
4. The administrator connects from the bastion to internal systems

Internal servers accept connections only from the bastion, not from the internet.

Key Security Characteristics

Hardened Configuration

Bastions run minimal software to reduce vulnerabilities. Unnecessary services are disabled, and operating system updates are tightly managed.

Strong Access Controls

Access is restricted using:

• IP allowlists
• Key based authentication
• Multi factor authentication
• Role based access

Centralized Logging

Every connection goes through the bastion, making it easier to:

• Audit who accessed what and when
• Detect suspicious behavior
• Meet compliance requirements

Common Use Cases

1. Cloud Infrastructure Management

Bastions are widely used in cloud environments to manage virtual machines that live in private networks.

2. Database and Backend Access

Databases often sit in private subnets and are accessed only through a bastion to prevent exposure.

3. Production System Operations

Sensitive production systems can be managed securely without opening inbound internet access.

Bastion vs Direct Access

Direct access exposes each system individually and increases attack surface.
A bastion limits exposure to one controlled gateway, reducing risk and improving oversight.

Best Practices

• Use one bastion per environment or region
• Apply strict firewall rules and network segmentation
• Enable session logging or recording
• Rotate credentials regularly
• Monitor and alert on unusual access patterns

In Short

A bastion is a security gate for your infrastructure. By forcing all administrative access through a single, well protected entry point, it reduces risk, improves visibility, and strengthens overall network security.