Picture this. You’re hosting an exclusive party. VIP guests only. You wouldn’t leave the front door wide open, right? Instead, you’d hire a bouncer, a no-nonsense gatekeeper who checks every invitation before letting anyone in.
That’s exactly what a bastion host (or jumpbox) does for your infrastructure. It stands between your private servers and the big, bad internet, ensuring only authorized users get through.
But like any good bouncer, it’s only effective if you train it well and don’t hand out VIP passes to everyone. So, let’s talk about best practices, both on-premise and in the cloud, to make sure your bouncer isn’t secretly letting in troublemakers.
The Basics: What’s a Bastion Host?
A bastion host is a hardened server that provides controlled access to your internal network. It usually serves as an SSH or RDP gateway, restricting direct access to critical infrastructure. The idea is simple: rather than exposing every server to external connections, you route access through a single, well-guarded entry point.
Why Not Just Use a VPN?
Good question. VPNs are great for securing remote access, but they tend to extend the network perimeter instead of limiting it. A compromised VPN credential could give an attacker broad access. Bastion hosts, on the other hand, act as a strict checkpoint.
Best Practices: On-Prem vs. Cloud
On-Prem Bastion Hosts
Running an on-prem bastion requires discipline. You have full control, but also full responsibility. Here’s what you need to get right:
- Minimal Attack Surface: Keep the OS footprint as small as possible. Disable unnecessary services, avoid installing GUI components, and use a minimal Linux distribution where feasible.
- Firewall Rules: The bastion should have strict firewall rules, only allowing SSH (or RDP) access from a predefined set of trusted IPs. Outbound traffic should also be restricted to limit exposure in case of a compromise.
- Multi-Factor Authentication (MFA): Passwords alone are not enough. Enforce MFA to ensure that even if a password is leaked, an attacker cannot easily gain access.
- Logging & Monitoring: Enable detailed logging for all access attempts and commands executed on the bastion. Forward logs to a SIEM (Security Information and Event Management) system for real-time monitoring and anomaly detection.
- Jump Proxy Instead of Direct Access: Users should never log into the bastion and then directly SSH into internal servers. Instead, set up a proxy mechanism that tunnels connections while keeping the bastion itself isolated.
- Regular Patching: Since bastions are high-value targets, they must be updated frequently. Implement an automated patching policy and reboot schedule to minimize downtime.
- Dedicated Account Policies: No shared admin accounts - every user should have their own credentials with granular permissions. Use role-based access control (RBAC) to ensure least privilege.
- Session Timeouts & Auto-Logout: Configure session timeouts to disconnect idle users. This prevents open sessions from becoming a security risk if a user’s device is left unattended.
- Dedicated Hardware or VM Isolation: If possible, run the bastion on dedicated hardware or a well-isolated VM to prevent lateral movement if compromised.
Cloud Bastion Hosts
Cloud environments offer more automation and security controls, but they also introduce new risks. Here’s how to handle it:
- Use Cloud-Native Services: Whenever possible, use managed services like AWS Session Manager, Azure Bastion, or Google Cloud IAP instead of rolling your own SSH gateway.
- Ephemeral Access: Don’t keep a bastion running 24/7. Use automation to spin up instances only when needed and terminate them after use.
- IAM-Based Access Control: Leverage cloud-native IAM policies to control who can access the bastion. Avoid using static SSH keys; instead, use IAM roles and temporary credentials.
- Restrict IP Access: Use security groups or firewall rules to allow only trusted IPs or dynamically managed ranges.
- Automate Patching: Enable automated updates and ensure that your cloud bastion instances are always running the latest security patches.
- Centralized Logging: Integrate with cloud security monitoring tools like AWS CloudTrail, Azure Security Center, or Google Security Command Center to collect and analyze access logs.
- Rotate Credentials: Regularly rotate SSH keys and access credentials. Use short-lived keys and avoid persistent credentials.
- Disable Direct Internet Access: A bastion should not have unrestricted outbound internet access. Lock it down to prevent data exfiltration.
- Monitor Access Patterns: Implement anomaly detection to flag unusual login patterns, such as access from unexpected locations or outside normal working hours.
Zero-Trust: The Future of Secure Access
Bastion hosts are great, but they aren’t the final word in secure access. Zero-trust architectures are shifting the focus from network-based controls to identity-based policies. Instead of opening a door to a trusted user, you verify every action regardless of where they are connecting from.
Zero-Trust Alternatives to Bastions
- Identity-Aware Proxies (e.g., Google BeyondCorp, AWS IAM policies)
- Just-in-Time Access (e.g., ephemeral SSH certificates, cloud-native session managers)
- Secure Workstations with Limited Access (e.g., CloudShell, hardened VDI solutions)
The goal? Reduce the number of open doors altogether.
Final Thoughts
If your infrastructure is still wide open, it’s time to put a bouncer at the door. A bastion host, or better yet, a zero-trust alternative, limits exposure and keeps attackers out.
Whether you’re on-prem or in the cloud, secure access is not a one-time setup - it’s an ongoing process. Keep refining your defenses, and don’t let bad habits turn your bastion into a backdoor.
Now go lock things down. Your infrastructure will thank you.