Securing Your AWS Infrastructure: Importance of Bastion Host

In cloud environments like AWS, security is always the top priority. When we launch resources inside a private subnet (like EC2 instances in a VPC), they are intentionally kept inaccessible from the internet to protect sensitive data.

But then arises a challenge:
How do we securely connect to these private instances for administration and troubleshooting?

That’s where the Bastion Host comes into play.

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What is a Bastion Host?

A Bastion Host (also known as a jump server) is a special-purpose EC2 instance that acts as a secure bridge between you and your private resources in AWS.

• It sits in the public subnet of your VPC.

• It has a public IP address (accessible via SSH or RDP from the internet).

• Once connected, you can SSH/RDP into private instances that don’t have public IPs.

Think of it like a guard at the entrance of your private network—no one gets in without passing through it.

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Why Use a Bastion Host in AWS?

1. Enhanced Security

   • Private EC2 instances don’t need public IPs.

   • Reduces the surface area for attacks.

2. Controlled Access

   • Only authorised users can connect to the bastion host.

   • Access can be restricted using Security Groups and IAM Policies.

3. Centralised Entry Point

   • Acts as a single gateway to your private resources.

   • Easier to monitor and log all activities.

4. Cost-Effective

   • Instead of assigning public IPs to multiple instances, you only maintain one secure bastion.

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How Bastion Host Works in AWS (Workflow)

1. User connects to Bastion Host via SSH/RDP.

2. From Bastion, the user connects to EC2 instances in a private subnet.

3. Security Groups control inbound/outbound traffic to allow this setup.

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Architecture Diagram

Here’s a simple diagram to illustrate how a Bastion Host works in AWS:

                   Internet
                       |
                [ Bastion Host ]
                 (Public Subnet)
                       |
      -----------------------------------
      |                                 |
 [ Private EC2 #1 ]              [ Private EC2 #2 ]
     (Private Subnet)                (Private Subnet)

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Best Practices for Bastion Hosts in AWS

• Always use key-based authentication instead of passwords.

• Apply the Principle of Least Privilege—restrict access to only required users.

• Enable logging and monitoring with AWS CloudWatch.

• Regularly patch and update the bastion host instance.

• Consider using AWS Systems Manager Session Manager for a more secure, keyless access alternative.

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Conclusion

A Bastion Host is a critical component in securing your AWS environment. It ensures that private instances remain protected while still being accessible when needed. By using bastion hosts along with AWS best practices, you can strike the perfect balance between security and usability in your cloud infrastructure.

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