Using SSH with a Jump Host to Securely Access Multiple VPS Instances

In today's cloud-based world, security is key. If you're running multiple VPS (Virtual Private Server) instances, keeping them locked behind a firewall is essential. But what if you need secure access to those servers? Enter the jump host, or bastion server—a secure middleman between your local machine and the VPS instances behind the firewall.

Instead of exposing each server to the internet, you limit SSH access to just the jump host. This makes your setup more secure while still offering seamless access to multiple VPS servers. Plus, if you're looking to purchase a VPS with robust SSH access, you can check out our SSH VPS options, which come with all the security features you need to set up and manage your infrastructure efficiently.

By funneling all your SSH traffic through a jump host, you reduce the attack surface and ensure that your VPS instances remain protected from unauthorized access.

What is a Jump Host (Bastion Server)?

Let’s start with the basics. A jump host, or bastion server, is a hardened server that acts as a gateway to other servers. It’s typically the only machine with an open SSH port that external users can connect to. Once you’re logged into the jump host, you can use it to reach other VPS instances behind the firewall, ensuring those servers are never directly exposed to the internet.

By funneling all your SSH traffic through the jump host, you significantly reduce the attack surface. If an attacker can’t get past your jump host, they can’t touch the VPS instances.

Benefits of Using a Jump Host

• Enhanced Security: Only the jump host has open access to the internet, reducing the number of vulnerable points.
• Centralized Access: You manage and control access from a single point, simplifying server management.
• Reduced Risk of Brute Force Attacks: By limiting external access to one machine, the risk of brute force attempts on other servers is minimized.
• Isolation: Even if the jump host is compromised (unlikely if properly configured), attackers still won’t have direct access to other servers.

How SSH Works with a Jump Host

In a typical scenario, you SSH directly into a VPS by typing a command like:

ssh user@vps_ip_address 

But when using a jump host, you first SSH into the jump host, then SSH from there to the VPS:

ssh user@jump_host_ip_address

ssh user@vps_ip_address

This method is functional, but it’s not the most efficient. Instead, you can configure your SSH client to automatically use the jump host as an intermediary, allowing you to SSH directly into a VPS while the jump host handles the behind-the-scenes routing.

Setting Up SSH with a Jump Host

Let's walk through the steps to configure SSH to work seamlessly with a jump host.

Step 1: Configure the Jump Host

First, you need to ensure that your jump host is properly set up and that you can access it via SSH. It’s important to secure this machine by using SSH keys rather than passwords and ensuring that only trusted IPs can access it.

1. Generate SSH Keys on your local machine (if you don’t have them already):

   ssh-keygen -t rsa -b 4096

2. Copy your public key to the jump host:

   ssh-copy-id user@jump_host_ip_address

3. Ensure SSH is locked down on the jump host by disabling password authentication and limiting login attempts.

Step 2: Set Up SSH Config File

Now, instead of having to manually SSH into the jump host and then the VPS, we can configure our local machine to automatically use the jump host as a relay. To do this, we’ll use the SSH config file.

1. Open your SSH configuration file on your local machine:

   nano ~/.ssh/config

2. Add the following configuration:

   Host jump_host

   HostName jump_host_ip_address

   User your_username

   IdentityFile ~/.ssh/id_rsa

   Host vps_instance_1

   HostName vps_ip_address_1

   User your_username

   ProxyJump jump_host

   Host vps_instance_2

   HostName vps_ip_address_2

   User your_username

   ProxyJump jump_host

   • Host jump_host: This defines the connection details for the jump host.
   • Host vps_instance_1 and vps_instance_2: These are the VPS instances you want to access. The ProxyJump directive tells SSH to use the jump host to reach these servers.

Step 3: Access VPS Instances

Once your SSH config file is set up, you can now directly access your VPS instances without needing to manually SSH into the jump host first.

For example, to SSH into vps_instance_1, simply run:

ssh vps_instance_1 

Your SSH client will automatically route you through the jump host and log you into the VPS.

Best Practices for Using a Jump Host

• Harden the Jump Host: Since the jump host is your main line of defense, it’s crucial to secure it properly. Disable password-based authentication, limit SSH access to specific IPs, and monitor for any unusual activity.
• Use Fail2Ban: Fail2Ban is a great tool to prevent brute force attacks by temporarily blocking IPs that show malicious activity.
• Regularly Update Software: Ensure your jump host and VPS instances are regularly updated with the latest security patches.
• Limit User Access: Only trusted users should have access to the jump host. Make sure to control permissions tightly.

FAQs

Q: Can I use a VPN instead of a jump host?

A: Yes, a VPN is another way to securely access VPS instances. However, a jump host is often preferred when you want tighter control over SSH access and don’t need full network access to the servers.

Q: Is it necessary to use SSH keys?

A: Absolutely. SSH keys provide far stronger security than password-based authentication. Always disable password logins on your servers.

Q: What if my jump host is compromised?

A: If a jump host is compromised, the attacker still doesn’t have direct access to the other VPS servers. However, it’s vital to detect and mitigate the breach quickly by rotating keys, updating configurations, and patching vulnerabilities.

Wrapping It Up

Using SSH with a jump host is one of the most effective ways to secure access to multiple VPS instances, particularly when they’re behind a firewall. By adding this extra layer of security, you minimize the risk of unauthorized access and centralize your SSH connections for easier management. Whether you’re managing a handful of servers or a large network, implementing a jump host can go a long way toward keeping your infrastructure safe and sound.

Remember, securing your servers isn’t just a one-time task—it’s an ongoing process. Stay vigilant, follow best practices, and you’ll greatly reduce the chances of a breach.