Use your own NAT Server to SAVE UPTO 40$ / MONTH

Introduction

Setting up a Virtual Private Cloud (VPC) in AWS can be challenging, especially when you have services in both public and private subnets. Recently, I worked on a project that required exactly this. We had a mix of services, some accessible from the internet and others tucked away in private subnets. To keep our private resources secure while still allowing them to reach out to the internet when needed, we needed something called a NAT—Network Address Translator.

Let me walk you through why we needed it, how it works, and the steps we took to set it up. I'll also touch on some real-world decisions we made, including a comparison of costs between using a NAT Gateway and a NAT instance.

Why We Needed a NAT

When you have resources in private subnets, they can't directly access the internet. This is because they have private IP addresses, which are great for security but don't work for reaching the outside world. But sometimes, these private resources need to download updates, connect to external APIs, or perform other tasks that require internet access.

This is where NAT comes into play. A NAT allows these private instances to connect to the internet by "borrowing" a public IP address temporarily. It’s like letting your private instances use a public passport for their internet trip. This way, they can stay secure while still getting the job done.

How a NAT Works

You might wonder, how does this NAT thing actually work? It's pretty simple. Because IPv4 addresses (the kind most people use) are in short supply, not every device can have a public IP. That's why we give public IPs only to those resources that absolutely need them, like the NAT.

Here’s what happens: When an instance in a private subnet needs to access the internet, it sends the request to the NAT. The NAT then masks the instance's private IP with its own public IP and sends the request to the internet. When the response comes back, the NAT forwards it to the original private instance. This way, the private instance gets what it needs without exposing its private IP to the internet.

Benefits of Using a NAT Gateway

In AWS, you have a few options for setting up NAT. One of the best choices is the AWS NAT Gateway. Here’s why:

• Reliable and Scalable: The NAT Gateway is fully managed by AWS. It’s reliable and can handle a lot of traffic without breaking a sweat. Plus, it scales automatically as your traffic increases.
• Simplified Management: Since AWS manages the NAT Gateway, you don’t have to worry about updates, maintenance, or scaling. It just works, letting you focus on more important tasks.
• Security: AWS takes care of the security patches and updates, so you don’t have to. This reduces the risk of vulnerabilities.

Disadvantages of Not Using a NAT Gateway

So, what happens if you decide not to use a NAT Gateway? You might think about setting up your own NAT instance, but there are some downsides:

• Manual Management: You’ll have to maintain and update the NAT instance yourself. If it fails, your private instances might lose internet access until you fix it.
• Limited Scalability: Unlike the NAT Gateway, your NAT instance won’t automatically scale with traffic. If your traffic spikes, the NAT instance might become a bottleneck.
• Complexity: Setting up and managing a NAT instance is more complex. You’ll need to configure security groups, route tables, and ensure everything is secure.
• Cost Considerations: While it might be cheaper initially, the ongoing management and potential downtime can increase the overall cost.

Possible Solutions for Implementing NAT

You have three main options when setting up NAT in AWS:

• AWS NAT Gateway: The best choice if reliability and scalability are your top priorities. It’s managed by AWS, so it’s easy to use, but it comes with a cost.
• IPv6 Routing: If you can use IPv6, this might be a great option. It’s free and simple to set up, but not all services support IPv6 yet.
• NAT Instance: A good option if you’re looking to save costs in a low-traffic scenario. You’ll use an EC2 instance to handle NAT tasks, but you’ll need to manage it yourself.

Cost Comparison: NAT Gateway vs. NAT Instance

Choosing between a NAT Gateway and a NAT instance often comes down to cost, especially if your traffic is light or you’re running on a tight budget. Let’s break down the costs of each:

NAT Gateway:

• Hourly Cost: $0.045 per hour.
• Data Transfer Cost: $0.045 per GB of data processed.
• Monthly Cost: For a typical month (730 hours), the base cost would be around $32.85, not including data transfer charges. With additional data transfer, costs can rise quickly.

NAT Instance:

• Instance Type: Let’s assume you use a t4g.micro instance.
• Hourly Cost: Approximately $0.0084 per hour.
• Data Transfer Cost: AWS charges for data transfer out to the internet, but there's no additional NAT-specific charge.
• Monthly Cost: The base cost for a t4g.micro would be around $6.13 per month (again, not including data transfer).

Note: The NAT Gateway is more expensive but offers greater reliability and scalability without the need for manual management. On the other hand, a NAT instance is cheaper to run, making it a good option for low-traffic environments where cost savings are crucial. However, it requires more hands-on management and doesn’t scale automatically with traffic.

Steps to Set Up a NAT Instance with Real-World Example

Let’s look into the steps we took to set up a NAT instance for a project at "TechCorp." We had a VPC with both public and private subnets and needed our private instances to access the internet securely.

• Deploying a VPC: We created a VPC with a public subnet (10.0.1.0/24) and a private subnet (10.0.2.0/24).
• Launching an EC2 Instance: We chose a t4g.micro instance type for the NAT, which is cost-effective for our needs. We assigned it a public IP in the public subnet.
• Configuring the EC2 Instance: We disabled source/destination checks on the instance and enabled IP forwarding by running:

echo "net.ipv4.ip_forward = 1" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

Then, we set up IP masquerading using iptables:

sudo iptables -t nat -A POSTROUTING -o ens5 -s 10.0.2.0/24 -j MASQUERADE

• Updating Route Tables: We updated the route table for the private subnet, directing all outbound traffic to the NAT instance.
• Configuring Security Groups: We allowed traffic from the private subnet to the NAT instance, ensuring secure communication.
• Testing the Setup: Finally, we SSHed into a private instance and used the tracepath command to verify that the traffic was correctly routed through the NAT instance.

CreateVpc | VPC Console

Common Questions

Here are some common questions that might pop up when working with NAT in AWS:

Q: Can I use the NAT instance as a bastion host to connect to my private instances?

A: Yes, you can, but there are pros and cons. Using the NAT instance as a bastion host can save money and reduce the number of EC2 instances you manage. However, this approach can create a single point of failure. If the instance goes down, you lose both NAT functionality and SSH access to your private instances. It also puts additional load on the instance, which might affect performance. To avoid these issues, it’s often better to use a separate bastion host.

Q: What if I only have light traffic—should I still go with a NAT Gateway?

A: For light traffic, a NAT instance might be more cost-effective. Just keep in mind the potential downsides, like manual management and limited scalability. If your traffic grows over time, you might want to switch to a NAT Gateway for better scalability and reliability.

Q: Is IPv6 a good alternative to using a NAT?

A: If your use case supports IPv6, it can be a great alternative. It’s free and doesn’t require a NAT for outbound internet access. However, not all AWS services fully support IPv6 yet, so it’s important to check compatibility before making the switch.

Conclusion

Setting up a NAT in AWS is essential for enabling secure internet access for your private instances. While there are different ways to implement NAT, choosing the right approach depends on your needs for reliability, scalability, and cost. Whether you go with AWS’s NAT Gateway or set up your own NAT instance, understanding these concepts will help you make informed decisions and keep your infrastructure secure and efficient.

If you have any questions or want to explore more advanced topics like automating NAT deployments or using Elastic IPs, feel free to reach out. I’m always happy to help with these topics!