We've all been there. You look at your monthly AWS bill, expecting the usual predictable numbers, only to find a massive spike staring back at you. Your mind starts racing, trying to figure out what went wrong. Did a script go rogue? Did traffic suddenly double?

Then you dig into the Cost Explorer and find the culprit: NAT Gateway.

It feels like a punch in the gut, especially when you realize you are being charged not just for having the gateway active, but for every single gigabyte of data that passes through it. If you are running data-heavy workloads, pulling large container images, or constantly talking to external APIs, NAT Gateway data processing fees can quickly become your biggest hidden cloud tax.

But you don't have to keep paying for things just because "that's how everyone else does it." If you want to take a meaningful step toward serious cost optimization, it's time to talk about a leaner, friendlier alternative: The NAT Instance.

The True Cost: NAT Gateway vs. NAT Instance

Before jumping into the fix, let's look at why NAT Gateway drains your wallet so fast. AWS charges ~$0.045/hour just for running a NAT Gateway (roughly $32.40/month before any data moves), plus $0.045 per GB of data processed. If your architecture moves terabytes of data to the internet or other AWS services outside your VPC, that processing fee stacks up fast, and it scales linearly with your traffic volume, so there are no volume discounts to save you.

A NAT Instance, on the other hand, changes the game entirely:

  • No Data Processing Fees: You pay strictly for the underlying EC2 instance size you choose. Whether you transfer 10 GB or 10 TB, the data processing cost is zero.
  • Flexible Pricing: You choose the instance family. Need a tiny setup for a staging environment? Throw a t4g.nano or t4g.micro at it for pennies a day.
  • Total Control: Because it is a standard EC2 instance running Linux, you can monitor traffic directly, apply custom firewall rules, or shut it down during off-hours to save even more.

Cost Comparison at Scale

Here is what the numbers actually look like for a typical workload in us-east-1:

Monthly Data Transfer NAT Gateway Cost NAT Instance (t4g.small) Savings
100 GB $32.40 + $4.50 = $36.90 ~$12.26 67%
1 TB $32.40 + $45.00 = $77.40 ~$12.26 84%
5 TB $32.40 + $225.00 = $257.40 ~$12.26 95%
10 TB $32.40 + $450.00 = $482.40 ~$12.26 97%

NAT Instance pricing: t4g.small On-Demand at ~$0.0168/hr. Standard EC2 data transfer rates apply (first 100 GB/month free, then $0.09/GB), but the per-GB NAT processing fee is eliminated entirely.

The numbers speak for themselves. For data-intensive workloads, the savings are dramatic.

Step-by-Step: Setting Up Your NAT Instance

Ready to break free from those never-ending billing surprises? Setting up a NAT Instance is straightforward. Here is how to do it.

Step 1: Launch the Instance

Note: AWS's legacy pre-configured NAT AMI (amzn-ami-vpc-nat) was built on Amazon Linux 1, which reached end-of-life in December 2023. You should use a modern Amazon Linux 2023 AMI and configure NAT manually (covered in Step 2), or use the community-maintained fck-nat AMI which automates the entire setup on a modern, ARM-based Graviton instance.

  1. Go to the EC2 Dashboard and click Launch Instance.
  2. Select Amazon Linux 2023 (ARM/Graviton for cost savings) or search for the fck-nat community AMI.
  3. Select an instance size that fits your bandwidth needs (a t4g.small handles up to 5 Gbps burst and is an excellent starting point).
  4. Launch it inside your Public Subnet. Ensure it receives a Public IP or attach an Elastic IP to it.

Step 2: Configure NAT with iptables

If you are using a standard Amazon Linux 2023 AMI (not fck-nat), you need to enable IP forwarding and set up masquerade rules. SSH into your instance and run:

# Enable IP forwarding (persists across reboots)
echo "net.ipv4.ip_forward = 1" | sudo tee /etc/sysctl.d/90-nat.conf
sudo sysctl -p /etc/sysctl.d/90-nat.conf

# Configure iptables to masquerade outbound traffic
sudo iptables -t nat -A POSTROUTING -o ens5 -j MASQUERADE

# Persist iptables rules across reboots
sudo yum install -y iptables-services
sudo service iptables save
sudo systemctl enable iptables

Replace ens5 with your instance's primary network interface name (check with ip link show).

Step 3: Disable Source/Destination Checking

This is the step everyone forgets. By default, EC2 instances only accept or send traffic if they are the source or destination. Because this instance will act as a middleman (routing traffic for other servers), you must turn this off.

  1. Select your new NAT Instance in the EC2 Console.
  2. Click Actions > Networking > Change Source/Destination Check.
  3. Set it to Stop/Disable.

Step 4: Update Your Route Tables

Now, you need to tell your private subnets to send their internet-bound traffic through your new instance instead of the old gateway.

  1. Go to the VPC Dashboard and select Route Tables.
  2. Find the Route Table associated with your Private Subnets.
  3. Edit the routes. Look for the destination 0.0.0.0/0.
  4. Change the target from your old nat-xxxxxxxxxxxx to your new Instance (i-xxxxxxxxxxxx).
  5. Save the changes.

Step 5: Lock Down with Security Groups

One often-overlooked advantage of a NAT Instance over NAT Gateway is Security Group support. NAT Gateways only support NACLs, but a NAT Instance can use Security Groups for fine-grained control:

  • Inbound Rule: Allow traffic from your private subnet CIDRs only (e.g., 10.0.2.0/24 and 10.0.3.0/24 on all ports).
  • Outbound Rule: Allow HTTPS (443) and HTTP (80) to 0.0.0.0/0, plus any specific ports your workloads need (e.g., 5432 for external PostgreSQL).
  • SSH Access: Restrict SSH (22) to your bastion host or VPN CIDR for management access.

This gives you far more granular control over what traffic is allowed to leave your VPC than a NAT Gateway can offer.

Making It Self-Healing with Auto Scaling

The biggest operational concern with a NAT Instance is availability: if the EC2 instance crashes, your private subnets lose internet access. You can mitigate this with a self-healing Auto Scaling Group:

Strategy: Create an ASG with a minimum, maximum, and desired capacity of 1. Pair it with a Launch Template and an Elastic IP. If the instance terminates (hardware failure, spot reclamation, etc.), the ASG automatically launches a replacement. Use a simple user data script to re-attach the Elastic IP and update the route table on boot:

#!/bin/bash
INSTANCE_ID=$(ec2-metadata -i | cut -d' ' -f2)
ALLOC_ID="eipalloc-0abcdef1234567890"        # Your Elastic IP allocation ID
ROUTE_TABLE_ID="rtb-0abcdef1234567890"        # Your private subnet route table

# Associate the Elastic IP
aws ec2 associate-address \
  --instance-id "$INSTANCE_ID" \
  --allocation-id "$ALLOC_ID" \
  --allow-reassociation

# Update the route table to point to this instance
aws ec2 replace-route \
  --route-table-id "$ROUTE_TABLE_ID" \
  --destination-cidr-block "0.0.0.0/0" \
  --instance-id "$INSTANCE_ID"

Make sure the instance's IAM Role has permissions for ec2:AssociateAddress and ec2:ReplaceRoute.

With this setup, recovery from an instance failure is typically under 2-3 minutes. That is not instant like NAT Gateway's built-in HA, but more than acceptable for non-production workloads.

The Reality Check: Feature Comparison

While the cost savings are dramatic, choosing a NAT Instance is a deliberate trade-off. Here is how they compare across every dimension:

Feature NAT Gateway NAT Instance
Management Fully managed by AWS You manage the OS, patching, and NAT config
Bandwidth Up to 100 Gbps (auto-scales) Limited by EC2 instance type (e.g., 5 Gbps for t4g.small)
Availability Multi-AZ redundant by default Single instance; needs ASG for self-healing
Data Processing Fee $0.045/GB None
Hourly Cost ~$0.045/hr ($32.40/mo) Depends on instance type (~$12/mo for t4g.small)
Security Groups ❌ Not supported (NACLs only) ✅ Full Security Group support
Port Forwarding ❌ Not supported ✅ Configurable with iptables
Bastion Host Combo ❌ Separate resource needed ✅ Can double as a bastion host

Drop the Expense, Keep the Performance

It is perfectly reasonable to change your architecture when the default options no longer serve your bottom line. You don't have to tolerate massive bills simply because a NAT Gateway is the standard recommendation.

If you run non-production environments, staging areas, or data pipelines that don't require 99.99% carrier-grade uptime, dropping the gateway for a NAT Instance is an easy, massive win for your monthly budget. Even for production workloads with moderate bandwidth needs, a properly configured NAT Instance with an Auto Scaling Group can deliver reliable service at a fraction of the cost.

Give it a try, monitor the performance, and enjoy watching your AWS bill shrink back down to where it belongs.