Inquiry on Primary-Failover Model and Zone Outage Handling for Azure NAT Gateway

Question

I am seeking clarification regarding the configuration of a primary-failover model for outbound traffic using Azure NAT Gateways. Have read the document https://learn.microsoft.com/en-us/azure/nat-gateway/nat-availability-zones. Specifically, I still have the following questions:

1. Primary-Failover Configuration:
   • Since Azure NAT Gateway routes outbound traffic automatically and does not support direct configuration of route tables for switching between multiple NAT Gateways (private IP is not exposed), what is the recommended approach for setting up a failover model? How can we configure traffic to seamlessly failover from the primary NAT Gateway to a secondary NAT Gateway in the event of a failure?
2. Handling Zone Outages:
   • If a NAT Gateway is deployed in a specific availability zone, and that zone experiences an outage, is it possible to disassociate the NAT Gateway from the affected subnet and automatically route traffic through a secondary NAT Gateway in another zone? If so, what steps or automation mechanisms are required to achieve this failover process without manual intervention?
3. Cost Considerations – Avoiding a Zonal Stack:
   • We would like to avoid creating a "zonal stack" by deploying a NAT Gateway in each availability zone due to cost concerns. Can you recommend an efficient solution that allows for high-availability failover across zones without incurring the cost of multiple NAT Gateways per zone?

We would greatly appreciate your guidance on how to design a cost-effective, high-availability NAT Gateway solution with automatic failover to ensure minimal disruption to outbound connectivity during an outage.

Answer 1

Hi Xiaoxi,

Greetings,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.

NOTE: A zonal promise for zone isolation scenarios exists when a virtual machine instance using a NAT gateway resource is in the same zone as the NAT gateway resource and its public IP addresses. The pattern you want to use for zone isolation is creating a "zonal stack" per availability zone. This "zonal stack" consists of virtual machine instances, a NAT gateway resource with public IP addresses or prefix on a subnet all in the same zone.

Primary-Failover Configuration

Azure NAT Gateway does not support direct configuration of route tables for switching between multiple NAT Gateways, as the private IP is not exposed. However, you can achieve a failover model by using a combination of Azure Load Balancer and NAT Gateway. Here’s a recommended approach:

1. Deploy an Azure Load Balancer: Use an internal load balancer to distribute outbound traffic across multiple NAT Gateways.
2. Configure Health Probes: Set up health probes to monitor the health of the NAT Gateways. If the primary NAT Gateway fails, the load balancer can automatically route traffic to the secondary NAT Gateway.
3. Use Azure Traffic Manager: For more advanced scenarios, you can use Azure Traffic Manager to manage traffic routing and failover between different regions or availability zones.

Handling Zone Outages

If a NAT Gateway is deployed in a specific availability zone and that zone experiences an outage, you can disassociate the NAT Gateway from the affected subnet and route traffic through a secondary NAT Gateway in another zone.

Cost Considerations – Avoiding a Zonal Stack

To avoid the cost of deploying a NAT Gateway in each availability zone, consider the following solution:

1. Use a Single NAT Gateway with Multiple Public IPs: Deploy a single NAT Gateway with multiple public IP addresses. This setup can handle high availability and failover without the need for multiple NAT Gateways per zone.
2. Leverage Azure Load Balancer: As mentioned earlier, use an internal load balancer to distribute traffic across multiple NAT Gateways, ensuring high availability without incurring additional costs.
3. Optimize Resource Allocation: Regularly review and optimize resource allocation to ensure cost-effectiveness while maintaining high availability.

Refer: https://learn.microsoft.com/en-us/azure/nat-gateway/nat-availability-zones?source=recommendations

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Hope this clarifies,

Thanks

Ganesh

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