Day 19: 𝐁𝐚𝐬𝐭𝐢𝐨𝐧 𝐇𝐨𝐬𝐭𝐬 / 𝐍𝐀𝐓 𝐈𝐧𝐬𝐭𝐚𝐧𝐜𝐞 / 𝐍𝐀𝐓 𝐆𝐚𝐭𝐞𝐰𝐚𝐲

𝐁𝐚𝐬𝐭𝐢𝐨𝐧 𝐇𝐨𝐬𝐭𝐬 / 𝐍𝐀𝐓 𝐈𝐧𝐬𝐭𝐚𝐧𝐜𝐞 / 𝐍𝐀𝐓 𝐆𝐚𝐭𝐞𝐰𝐚𝐲 :

👉 Bastion Host to SSH into our private EC2 instances in private subnets

👉 NAT Instance Allows EC2 in private subnets to connect to the Internet

👉 AWS-managed NAT Instance is called NAT Gateway, Requires IGW

👉 Egress-only Internet Gateway similar to a NAT Gateway but for IPv6

1. Bastion Host:

• Purpose: A bastion host is a server that acts as a secure gateway between your private network (private subnets) and the outside world (public internet).
• Functionality: It is used for secure remote access (typically via SSH) to your private EC2 instances located in private subnets.
• Security Considerations: The bastion host is configured with strict security measures, allowing only authorized users to access it. Once connected to the bastion host, users can then use it as a jump server to access other resources in the private network.

2. NAT Instance:

• Purpose: Network Address Translation (NAT) instances allow EC2 instances in private subnets to establish outbound connections to the internet while keeping them hidden behind the NAT instance’s public IP.
• Functionality: When an EC2 instance in a private subnet wants to communicate with the internet (e.g., for software updates), it sends its traffic to the NAT instance, which then forwards the traffic to the internet and returns the responses back to the EC2 instance.
• Security Considerations: NAT instances need to be configured securely, and only necessary traffic should be allowed. They play a crucial role in enhancing the security of private subnets by limiting direct internet access.

3. NAT Gateway:

• Purpose: Similar to a NAT instance, a NAT Gateway allows EC2 instances in private subnets to connect to the internet, but it is a managed service provided by AWS.
• Functionality: It is a highly available, scalable, and managed solution. It requires the configuration of an Internet Gateway (IGW) for outbound traffic. It simplifies the setup compared to managing your NAT instances.
• Security Considerations: NAT Gateway is managed by AWS, so you don’t need to worry about its maintenance. Security groups and route tables should be configured appropriately to control traffic flow.

4. Egress-only Internet Gateway (EOIG):

• Purpose: This is specific to IPv6. An Egress-only Internet Gateway allows IPv6-enabled instances in your VPC to initiate outbound connections to the internet while preventing unsolicited inbound traffic from reaching them.
• Functionality: It provides similar functionality to a NAT Gateway but for IPv6 traffic. It’s necessary when your VPC uses IPv6 addresses, and you want your instances to communicate with the IPv6 internet.
• Security Considerations: Like other components, security groups and route tables should be configured to control the traffic. EOIG helps in maintaining the security of IPv6-enabled instances in private subnets.

1. Secure Remote Access to Private Instances:

• Use Case: Your organization has critical applications running on EC2 instances in private subnets for security reasons. You need a secure way for authorized administrators to access these instances for maintenance or troubleshooting.
• Solution: Deploy a bastion host in a public subnet. Authorized users can SSH into the bastion host, and from there, they can jump to the private instances using private IP addresses. This adds an extra layer of security and control to remote access.

2. Outbound Internet Access for Private Instances:

• Use Case: Your application instances in private subnets require access to the internet for tasks such as software updates, license validation, or fetching external data. However, you want to avoid direct internet exposure for these instances.
• Solution: Implement a NAT Gateway or NAT instance in a public subnet. Route the outbound traffic from private instances through the NAT, ensuring that the private instances don’t have direct internet access. This helps in controlling and monitoring outbound traffic.

3. IPv6 Connectivity for Private Instances:

• Use Case: Your organization is adopting IPv6, and you have EC2 instances in private subnets that need to communicate with the IPv6-enabled internet.
• Solution: Set up an Egress-only Internet Gateway (EOIG) to allow IPv6-enabled instances in private subnets to initiate outbound connections. This ensures that your IPv6 instances can access the IPv6 internet securely while preventing unsolicited inbound traffic.