Lambda VPC NAT Gateway Cost Warning

What this rule checks

Warns about potential NAT Gateway costs for VPC-attached Lambda functions.

How to fix it

1. 1Use VPC endpoints instead of NAT Gateway where possible
2. 2Consider if VPC attachment is necessary
3. 3Monitor NAT Gateway data processing costs

import * as ec2 from 'aws-cdk-lib/aws-ec2';
import * as lambda from 'aws-cdk-lib/aws-lambda';

// inside your Stack
const vpc = new ec2.Vpc(this, 'Vpc', { maxAzs: 1 });
new lambda.Function(this, 'Fn', {
  runtime: lambda.Runtime.NODEJS_22_X,
  handler: 'index.handler',
  code: lambda.Code.fromInline('exports.handler = async () => {};'),
  vpc,
});

import * as ec2 from 'aws-cdk-lib/aws-ec2';
import * as lambda from 'aws-cdk-lib/aws-lambda';

// inside your Stack
const vpc = new ec2.Vpc(this, 'Vpc', {
  natGateways: 0,
  subnetConfiguration: [
    { name: 'isolated', subnetType: ec2.SubnetType.PRIVATE_ISOLATED },
  ],
});
new lambda.Function(this, 'Fn', {
  runtime: lambda.Runtime.NODEJS_22_X,
  handler: 'index.handler',
  code: lambda.Code.fromInline('exports.handler = async () => {};'),
  vpc,
  vpcSubnets: { subnetType: ec2.SubnetType.PRIVATE_ISOLATED },
});

CDK Insights pinpoints the exact file and line in your CDK source for every finding, so you can jump straight to the fix.

Affected resource types

Intentional? Suppress this finding

Sometimes a flag is deliberate — a genuinely public endpoint, say. You can dismiss lambda-vpc-nat-cost and the reason is kept in the report, not silently hidden.

In .cdk-insights.json:

{
  "ignoreRules": [
    { "id": "lambda-vpc-nat-cost", "reason": "Why this is intentional" }
  ]
}

Or inline in your CDK code:

Validations.of(scope).acknowledge({
  id: 'cdk-insights::lambda-vpc-nat-cost',
  reason: 'Why this is intentional',
});

Use the rule ID lambda-vpc-nat-cost shown above — not the CDK-* ID from SARIF / GitHub code scanning. To dismiss every finding on one construct instead, use ignorePaths. Suppression docs →

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