The Cost of High Availability: Multi-AZ NAT Gateways

The “Well-Architected Framework” says: Deploy a NAT Gateway in every Availability Zone. Your CFO says: Why is the network bill $1,000?

Let’s reconcile reliability with reality.

The Cost of “Perfect”

Running 3 NAT Gateways (us-east-1a, 1b, 1c) costs:

• Fixed: $32.85 * 3 = $98.55 / month.
• Processing: $0.045/GB (Same volume).

The premium you pay for “HA” is roughly $65/month (the cost of the 2 extra gateways).

What happens if you DON’T do it?

If you run only 1 NAT Gateway in AZ A:

1. Scenario: AZ A goes down.
2. Impact: Instances in AZ B and C cannot reach the internet. They cannot pull images, sending logs, or call Stripe/Twilio.
3. Result: Your app is effectively down, even if the web servers are technically up.

The Middle Ground

For Production: Pay the $65. It is cheap insurance. For Non-Production: Do not pay it.

Staging Architecture:

• One NAT Gateway in AZ A.
• Route tables in AZ B and C point to the gateway in AZ A.
• Risk: If AZ A dies, Staging is down.
• Cost: You pay cross-AZ fees ($0.02/GB) but save the fixed hardware cost ($65).

[!TIP] Find your break-even. Cross-AZ fees can exceed the savings if traffic is high. Plug your numbers into our NAT Gateway Pricing Calculator to confirm if the “Middle Ground” is actually cheaper.