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

Modularized approach with separate constructs

• attach multiple InternalApiGateway and InternalWebsite constructs to the same Internal Service to save costs and keep flexibility

Internal Service Construct (mandatory construct):

• creates an internal application loadbalancer
  • forwards traffic to VPC endpoint for execute-api
  • redirect http to https
• generates custom domains for the API Gateway
• generates certificates for the loadbalancer listener

Internal Api Gateway Construct:

• 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
• attaches custom domains to the API Gateway
• attaches certificates to the the API Gateway and the loadbalancer

Internal Website Construct:

• makes your website internally accessible
• redeploys your website with a single cdk deploy
• provides a securely configured private s3 bucket out of box
• works with SPA applications (written with Vue, Angular) and static websites
• is an extension of the InternalApiGateway Construct

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...