Technical Investigation Request – NAT Gateway 1TB Data Processing Usage Spike

Question

Technical Investigation Request – NAT Gateway 1TB Data Processing Usage Spike

Anonymous

We have observed that our NAT Gateway has processed approximately 1 TB of data in the current billing month, resulting in a significant increase in cost.

The Azure billing team has reviewed the charges and confirmed that the consumption is valid from a metering perspective. They advised us to contact the technical team to analyze the source of this high data processing usage.

We request your support to investigate the following:

Identify which resources ( AKS nodes, App Services, etc.) are routing traffic through the NAT Gateway.

Provide a breakdown of outbound data traffic contributing to the 1 TB usage.

Confirm whether the traffic is internet-bound or service-to-service communication.

Check for any abnormal or unexpected traffic patterns.

Suggest optimization recommendations to reduce NAT Gateway data processing costs.

Please let us know if you require any additional details such as subscription ID, resource group name, or timeframe for analysis.

We appreciate your assistance in identifying the root cause and recommending cost optimization measures.

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Answer 1

Hi @Mohammed Suhail,

Thank you for reaching out on the Microsoft Q&A forum.

When a NAT Gateway is associated with a subnet, it becomes the default outbound path. All internet‑bound traffic from resources in that subnet (VMs, AKS node pools, VMSS, App Service VNet integration) flows through the NAT Gateway, regardless of the originating resource. Docs: Azure NAT Gateway overview [learn.microsoft.com]

Microsoft provides NAT Gateway metrics and flow logs to analyze traffic. The Bytes metric shows total data processed. StandardV2 NAT Gateway Flow Logs provide source private IP, destination IP, and bytes sent/received, enabling attribution to specific workloads.

To collect these logs, NatGatewayFlowLogsV1 must be enabled via Diagnostic settings on the NAT Gateway resource and sent to Log Analytics, Storage Account, or Event Hub. Docs: Enable NAT Gateway flow logs via Diagnostic settings [learn.microsoft.com], [docs.azure.cn]

Traffic going to public endpoints (internet or Azure PaaS over public URLs) is processed and billed by the NAT Gateway. Traffic using Private Endpoint / Private Link stays on the Azure backbone and does not traverse the NAT Gateway. Docs: Design with NAT Gateway and Private Link [learn.microsoft.com]

To reduce future NAT Gateway data processing charges, Microsoft recommends using Private Endpoints for Azure PaaS, reviewing high‑egress workloads, and continuously monitoring usage with Azure Monitor and Cost Management. Docs: Virtual Network cost optimization principles [learn.microsoft.com]

Kindly let us know if the above helps or if you need further assistance.

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