Cloud Development Kit examples

Environment specifics using CDK Context

Gerald Stewart recently posted a nice article which describes how to deal with Environment specifc configurations when deploying your stacks. In this example below I will go through a complete example using AWS Lambda where we set the API endpoints as environment variables. This might help to see how a full implementation could look like.

Bootstrap with Projen

To get our CDK project started I like to use projen which takes care of a lot of bootstrapping for projects. To install it you can follow the projen guide on Projen but you really just need to install it globally using ‘npm -g install projen’ or the yarn equivalent.

When its available on your shell you run the below to bootstrap your new project file.

projen new awscdk-app-ts 

Setting up cdk.context.json

The method I’ve followed here is Gerald’s number 2 option which is the one I tend to use. In the example I’ve set two API endpoints, one for spacetraders and another for openweather which we will need to load into the lambda.

cdk.context.json

{
  "development": {
    "spacetraders": "https://dev-api.spacetraders.io/game/status",
    "openweather": "https://dev-api.openweathermap.org/data/2.5/weather?q={city name}&appid={API key}"
  },
  "test": {
    "spacetraders": "https://test-api.spacetraders.io/game/status",
    "openweather": "https://test-api.openweathermap.org/data/2.5/weather?q={city name}&appid={API key}"
  },
  "production": {
    "spacetraders": "https://api.spacetraders.io/game/status",
    "openweather": "https://api.openweathermap.org/data/2.5/weather?q={city name}&appid={API key}"
  }
}

Configuring CDK using the high level NodeJSFunction Construct

The next step is we can create an Interface which defines how the endpoints are loaded. CDK supports strings when using the scope.node.tryGetContext helper.

With that now out of the way we can use the handy NodejsFunction helper for CDK which will transpile our code using esbuild into a minified version of the code for fast startup times.

index.ts

import * as lambda from '@aws-cdk/aws-lambda-nodejs';

interface EndPointConfig {
  readonly spacetraders: string;
  readonly openweather: string;
}

export class MyStack extends Stack {
  constructor(scope: Construct, id: string, props: StackProps = {}) {
    super(scope, id, props);

    const environment: string = process.env.ENV_NAME || 'development';
    const envConfig: EndPointConfig = scope.node.tryGetContext(environment);

    new lambda.NodejsFunction(this, 'MyFunction', {
      entry: './functions/hello/index.ts',
      environment: {
        SPACETRADERS_API: envConfig.spacetraders,
        OPENWEATHER_API: envConfig.openweather,
      },
      handler: 'index.handler',
    });
  }
}

Running a “cdk synth” locally on the project will now generate a cloudformation template where we see the Environment Variables are loaded.

  MyFunction3BAA72D1:
    Type: AWS::Lambda::Function
    Properties:
      Role:
        Fn::GetAtt:
          - MyFunctionServiceRole3C357FF2
          - Arn
      Environment:
        Variables:
          SPACETRADERS_API: https://api.spacetraders.io/game/status
          OPENWEATHER_API: https://api.openweathermap.org/data/2.5/weather?q={city name}&appid={API key}
          AWS_NODEJS_CONNECTION_REUSE_ENABLED: "1"
      Handler: index.index.handler
      Runtime: nodejs14.x

Hopefully this was helpful in how this all fits together in a simplified Lambda.