cdk-internal-gateway

CDK Internal Gateway

Use this CDK construct to create internal serverless applications.

Useful for larger companies to create internal serverless applications that are not exposed to the internet and only accessible from the internal network.

Installation

Using Typescript for aws cdk

npm i cdk-internal-gateway

Using Python for aws cdk

pip install pharindoko.cdk-internal-gateway

Architecture

Technical Details

• creates an internal application loadbalancer
  • forwards traffic to VPC endpoint for execute-api
  • redirect http to https
• provides a securely configured apigateway resource out of the box
  • attach your aws components to the internal apigateway resource
  • sets api gateway to PRIVATE mode
  • sets resource policies to only allow traffic from vpc endpoint
• generates and attaches custom domains to the API Gateway
• generates and attaches certificates to the the API Gateway and the loadbalancer
• modularized approach with separate constructs
  • add multiple internal api gateways to the same internal service to save costs and keep flexibility

Requirements

• CDK V2 (2.46.0)
• A VPC
• A VPC Endpoint for execute-api
• A Hosted Zone
• Internally accessible subnets (for the load balancer)

Usage

Let`s assume we create a simple internal api for our company and start with a single lambda function...

1. Create a file called /lib/my-new-stack.ts

   import { aws_apigateway as apigateway, aws_ec2 as ec2, aws_lambda as lambda, aws_route53 as route53, Stack, StackProps } from 'aws-cdk-lib';
   import { HttpMethod } from 'aws-cdk-lib/aws-events';
   import { InternalApiGateway, InternalApiGatewayProps, InternalService } from 'cdk-internal-gateway';
   import { Construct } from 'constructs';
   import * as path from 'path';
   
   // Create a new stack that inherits from the InternalApiGateway Construct
   export class ServerlessStack extends InternalApiGateway {
       constructor(scope: Construct, id: string, props: InternalApiGatewayProps) {
           super(scope, id, props);
   
           // The internal api gateway is available as member variable
           // Attach your lambda function to the this.apiGateway
           const defaultLambdaJavascript = this.apiGateway.root.resourceForPath("hey-js");
           const defaultHandlerJavascript = new lambda.Function(
               this,
               `backendLambdaJavascript`,
               {
                   functionName: `js-lambda`,
                   runtime: lambda.Runtime.NODEJS_14_X,
                   handler: "index.handler",
                   code: lambda.Code.fromAsset(path.join(__dirname, "../src")),
               }
           );
   
           defaultLambdaJavascript.addMethod(
               HttpMethod.GET,
               new apigateway.LambdaIntegration(defaultHandlerJavascript)
           );
       }
   }
   
   // Create a new stack that contains the whole service with all nested stacks
   export class ServiceStack extends Stack {
       constructor(scope: Construct, id: string, props: StackProps) {
           super(scope, id, props);
   
           // get all parameters to create the internal service stack
           const vpc = ec2.Vpc.fromLookup(this, 'vpcLookup', { vpcId: 'vpc-1234567890' });
           const subnetSelection = {
               subnets: ['subnet-0b1e1c6c7d8e9f0a2', 'subnet-0b1e1c6c7d8e9f0a3'].map((ip, index) =>
                   ec2.Subnet.fromSubnetId(this, `Subnet${index}`, ip),
               ),
           };
           const hostedZone = route53.HostedZone.fromLookup(this, 'hostedzone', {
               domainName: 'test.aws1234.com',
               privateZone: true,
               vpcId: vpc.vpcId,
           });
           const vpcEndpoint =
               ec2.InterfaceVpcEndpoint.fromInterfaceVpcEndpointAttributes(
                   this,
                   'vpcEndpoint',
                   {
                       port: 443,
                       vpcEndpointId: 'vpce-1234567890',
                   },
               );
   
           // create the internal service stack
           const serviceStack = new InternalService(this, 'InternalServiceStack', {
               hostedZone: hostedZone,
               subnetSelection: subnetSelection,
               vpcEndpointIPAddresses: ['192.168.2.1', '192.168.2.2'],
               vpc: vpc,
               subjectAlternativeNames: ['internal.example.com'],
               subDomain: "internal-service"
           })
   
           // create your stack that inherits from the InternalApiGateway
           new ServerlessStack(this, 'MyProjectStack', {
               domains: serviceStack.domains,
               stage: "dev",
               vpcEndpoint: vpcEndpoint,
           })
   
           // create another stack that inherits from the InternalApiGateway
           ... 
           ...
       }
   }
   

2. Reference the newly created ServiceStack in the default /bin/{project}.ts file e.g. like this

   new ServiceStack(app, 'MyProjectStack', {
   env:
   {
       account: process.env.CDK_DEPLOY_ACCOUNT || process.env.CDK_DEFAULT_ACCOUNT,
       region: process.env.CDK_DEPLOY_REGION || process.env.CDK_DEFAULT_REGION
   }
   

Costs

You have to expect basic infra costs for 2 components in this setup:

Count	Type	Estimated Costs
1 x	application load balancer	20 $
2 x	network interfaces for the vpc endpoint	16 $

A shared vpc can lower the costs as vpc endpoint and their network interfaces can be used together...