AWS NAT Gateways Are Robbing You 💀💸

If you've ever looked at your AWS bill and winced at the NAT Gateway charges, you're not alone. While NAT Gateways are essential for allowing private subnet resources to access the internet, their cost can quickly spiral out of control, especially in multi-region or high-throughput environments. What if there was a modern, cost-effective alternative that could slash your NAT costs by up to 90% without sacrificing functionality? Enter fck-nat – a (f)easible (c)ost (k)onfigurable NAT solution that challenges the existing NAT Gateway pricing model

Of course, nothing comes without trade-offs. While fck-nat delivers impressive cost savings, you'll be trading AWS's managed convenience for self-managed infrastructure, which means taking responsibility for availability, failover complexity, and operational overhead. But for many organizations, these drawbacks are a small price to pay for the substantial cost reductions and increased control over their network infrastructure.

Understanding AWS NAT Gateway

Network Address Translation (NAT) Gateways serve a critical role in AWS architecture by enabling resources in private subnets to initiate outbound connections to the internet while preventing inbound traffic from reaching them directly. This is essential for tasks like accessing external APIs or pulling container images – all while maintaining the security posture of keeping your infrastructure in private subnets.

The problem isn't functionality – AWS NAT Gateways work flawlessly. The issue is cost. AWS charges for NAT Gateways in two ways: an hourly rate (approximately $43 USD per month per gateway) and data processing fees ($0.059 USD per GB processed). For organizations running multiple environments, regions, or handling significant data throughput, these costs compound rapidly. A single NAT Gateway processing 1TB of data monthly costs around $103 USD, and that's before considering the hourly charges.

To achieve high availability, you need to deploy NAT Gateways across multiple availability zones – typically 2-3 per region. This means your $43 USD monthly cost per gateway becomes $86-129 USD just for the base hourly charges, before any data processing. Scale this across multiple availability zones and regions, and you're looking at thousands of dollars in NAT Gateway costs alone.

The Self-Managed Alternative Challenge

Given these costs, the natural question becomes: can you manage your own NAT gateway? AWS does provide a NAT Instance AMI as an alternative, but here's where things get problematic. The official AWS-supported NAT Instance AMI hasn't been updated since 2018 and is still running Amazon Linux 1, which reached end-of-life status years ago. This outdated approach offers no ARM support, meaning it can't leverage EC2's most cost-effective instance types like the modern Graviton processors.

Running outdated, unsupported software in production isn't just a security risk - it's a compliance nightmare. Organizations need a modern, maintained solution that can deliver the cost savings of self-managed infrastructure without the risks of abandoned software. This is where the motivation for a better solution becomes clear: significant cost savings shouldn't require compromising on security or maintainability.

Introducing fck-nat

fck-nat is a modern, open-source NAT solution built on current Amazon Linux AMIs that transforms any EC2 instance into a fully functional NAT gateway. Unlike AWS's abandoned NAT Instance AMI, fck-nat is actively maintained, regularly updated, and supports both x86 and ARM architectures, allowing you to deploy on cost-effective instance types like t4g.nano.

The cost difference is dramatic. Here's a direct comparison of the pricing structure for ap-southeast-2:

While an AWS managed NAT Gateway costs approximately $42.48 USD per month plus data processing fees, a t4g.nano instance running fck-nat costs around $3.81 USD per month with no additional data processing charges. This represents potential savings of over 90% on your NAT infrastructure costs. For organizations processing terabytes of data monthly, the savings can reach thousands of dollars USD per month per NAT gateway replaced.

Note that the t4g.nano instance shown in this comparison is suitable for light to moderate workloads. For higher bandwidth requirements, you may need larger instance types, which will increase costs but still remain significantly cheaper than managed NAT Gateways. For detailed guidance on selecting the appropriate instance size based on your bandwidth needs, visit the fck-nat instance sizing guide.

Beyond cost savings, fck-nat offers the flexibility and control that managed services can't provide. You can customize routing rules, implement additional security measures, and integrate with your existing monitoring and logging infrastructure. The solution is packaged as an easy-to-deploy AMI that requires minimal configuration to get up and running.

fck-nat also exports a number of useful metrics that give parity with the Managed NAT Gateway. Information about the metrics can be found in the fck-nat features documentation.

Migration Guide: Replacing Your NAT Gateway

Migrating from AWS NAT Gateway to fck-nat can be accomplished with minimal disruption using Infrastructure as Code. Here's a step-by-step migration process:

Step 1: Deploy the fck-nat instance

# Get the latest fck-nat AMI
data "aws_ami" "fck_nat" {
  most_recent = true
  owners      = ["568608671756"] # fck-nat official account

  filter {
    name   = "name"
    values = ["fck-nat-al2023-*"]
  }

  filter {
    name   = "architecture"
    values = ["arm64"] # Use ARM for cost savings
  }
}

# Create security group for fck-nat
resource "aws_security_group" "fck_nat" {
  name_prefix = "fck-nat-"
  vpc_id      = aws_vpc.main.id

  ingress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["10.0.0.0/16"] # Update to match your actual VPC CIDR
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_network_interface" "fck-nat-if" {
  subnet_id       = aws_subnet.subnet_public.id
  security_groups = [aws_security_group.fck_nat.id]

  source_dest_check = false
}

resource "aws_instance" "fck_nat" {
  ami           = data.aws_ami.fck_nat.id
  instance_type = "t4g.nano"

  network_interface {
    network_interface_id = aws_network_interface.fck-nat-if.id
    device_index         = 0
  }

  tags = {
    Name = "fck-nat"
  }
}

Note: For production environments, consider deploying fck-nat with Auto Scaling Groups for automatic failover.

Step 2: Update your route table

# Create/update private route table to use fck-nat instance
resource "aws_route" "private_nat" {
  route_table_id         = aws_route_table.private.id
  destination_cidr_block = "0.0.0.0/0"
  network_interface_id   = aws_network_interface.fck-nat-if.id
}

Step 3: Remove the old NAT Gateway (after testing)

# Comment out or remove these resources after migration
# resource "aws_nat_gateway" "main" { ... }
# resource "aws_eip" "nat" { ... }

Step 4: Verify connectivity

# Test from an instance in your private subnet
curl -I https://www.mechanicalrock.io

Understanding the Trade-offs

While fck-nat offers significant cost savings, it's important to understand the trade-offs involved in moving from a managed service to a self-managed solution.

Availability Considerations: Unlike AWS's managed NAT Gateway, which offers built-in high availability, you're responsible for the uptime of your fck-nat instances. Instance replacements or maintenance will result in temporary connectivity loss for resources in private subnets. Additionally, switching traffic away from an unhealthy fck-nat instance isn't as straightforward as it might seem – it requires updating route table entries to point to a backup instance, which involves API calls and propagation time that can take several minutes.

The failover process typically involves detecting the unhealthy instance (through health checks or monitoring), launching a replacement instance or activating a standby, updating the route table to redirect traffic, and ensuring the new instance has assumed the correct network configuration. This complexity means that unlike managed NAT Gateways that handle failover transparently, you need to architect and test your own high availability solution.

Fortunately, fck-nat supports several advanced features to improve availability and operational simplicity:

• Auto Scaling Groups can automatically replace failed instances and maintain consistent capacity, reducing manual intervention during outages
• Static IP addresses can be assigned to instances, ensuring external services that require IP whitelisting continue to work seamlessly during instance replacements. More details available in the fck-nat static IP documentation

These can be combined with traditional strategies like running multiple fck-nat instances across availability zones with automated failover scripts, implementing robust health monitoring with quick detection times, or scheduling maintenance during low-usage periods.

Security Group Limitations: EC2 security groups have stateful connection tracking limits that can be reached under high connection volumes. For high-throughput scenarios, you can bypass these limitations by replacing security groups with iptables rules directly on the instance, giving you more granular control and higher connection limits. Alternatively, you may need to implement connection pooling, deploy multiple NAT instances, or consider whether the managed NAT Gateway's higher connection limits justify the cost difference.

Bandwidth Considerations: While fck-nat can achieve impressive throughput, it's ultimately limited by the network performance of the underlying EC2 instance type. For applications requiring consistent multi-gigabit throughput, AWS's managed NAT Gateway may still be the better choice. However, for most workloads, appropriately sized fck-nat instances provide more than adequate performance at a fraction of the cost.

For detailed guidance on selecting the right instance size for your bandwidth requirements, the fck-nat project provides comprehensive documentation that includes performance benchmarks and sizing recommendations.

The Takeaway

The choice between AWS managed NAT Gateway and fck-nat ultimately comes down to your priorities: managed convenience versus cost optimization. For organizations looking to reduce their AWS bills without sacrificing functionality, fck-nat represents a compelling alternative that can deliver 90%+ cost savings while providing greater flexibility and control.

When evaluating NAT solutions for your AWS infrastructure:

• Calculate the true cost including hourly rates, data processing fees, and high availability requirements
• Consider your operational capabilities and willingness to manage infrastructure
• Evaluate your performance requirements against instance type limitations
• Plan for failover complexity and the operational overhead of self-managed solutions

The solution is particularly attractive for development environments, smaller production workloads, or any scenario where the managed service premium doesn't align with your budget constraints. With active maintenance, modern Linux distributions, and ARM support, fck-nat addresses the shortcomings of AWS's abandoned NAT Instance AMI while delivering the cost benefits that drove interest in self-managed solutions in the first place.

But if you really want to optimize your cloud costs while maintaining reliability and performance, you need more than just switching NAT solutions. You need a team that understands how to architect cost-effective, scalable infrastructure from the ground up.

That's where Mechanical Rock comes in. We help teams design and implement cloud architectures that balance cost, performance, and operational simplicity. Get in touch if you want to discuss how we can help your team build better, more cost-effective infrastructure.