CDK Typescript library

Getting started

yarn add @aws-abaschen/cdk-typescript
mkdir -p src/{functions,layers}

Refer to this example Stack and the related CDK App

NodetsFunction

This construct will allow your lambdas to output .mjs files with their source maps. It relies on standardized folder structure in src/ Each Lambda function will have to be written in a folder which will become its functionName in src/functions/{functionName}/index.ts.

All the default values are for example purpose and doesn't reflect any recommendation nor will be maintained.

IAM Role and Policies

Instead of letting CDK generating a role, the construct will create one named fnRole${id} and will append the policies below with a Stack id fn-role-${id}. The property role is also available for further manipulation.

1. Logging

By default, the PolicyStatement to write in the log group will be added:

new PolicyStatement(
    {
        effect: Effect.ALLOW,
        actions: [
            "logs:CreateLogGroup",
            "logs:CreateLogStream",
            "logs:PutLogEvents",
        ],
        resources: [`arn:aws:logs:${Stack.of(this).region}:${scope.account}:log-group:/aws/lambda/${id}:*`]
    }
);

2. VPC

Adding a VPC to your lambda function will automatically add the policy to connect:

new PolicyStatement({
    effect: Effect.ALLOW,
    actions: [
        "ec2:CreateNetworkInterface",
        "ec2:DescribeNetworkInterfaces",
        "ec2:DeleteNetworkInterface",
        "ec2:AssignPrivateIpAddresses",
        "ec2:UnassignPrivateIpAddresses"
    ],
    resources: ["*"]
});

3. Tracing

Tracing is enabled by default and the policy statement will be added unless disabled:

new PolicyStatement({
        effect: Effect.ALLOW,
        actions: [
            "logs:CreateLogDelivery",
            "logs:DeleteLogDelivery",
            "logs:DescribeLogGroups",
            "logs:DescribeResourcePolicies",
            "logs:GetLogDelivery",
            "logs:ListLogDeliveries",
            "logs:PutResourcePolicy",
            "logs:UpdateLogDelivery",
            "xray:GetSamplingRules",
            "xray:GetSamplingTargets",
            "xray:PutTelemetryRecords",
            "xray:PutTraceSegments"
        ],
        resources: [`arn:aws:logs:${Stack.of(this).region}:${scope.account}:log-group:/aws/lambda/${id}:*`],
})

SSM String parameters

String parameters can be automatically referenced and read policy applied if they follow a specific prefix (default here is fn-). They will then get injected as an environment variable with PARAM_ prefix and - (dash) replaced with _ (underscore) in the name:

new NodetsFunction(this, name, {
    parameters: ['DB-USER'],
    environment: {
        TEST_1: 'test Value 1'
    }
});

Will output:

[...]
      Environment:
        Variables:
          NODE_OPTIONS: --enable-source-maps
          PARAM_DB_USER:
            Ref: discordpongfnparamDBUSERParameter70CB30BD
          TEST_1: test Value 1
          AWS_NODEJS_CONNECTION_REUSE_ENABLED: "1"
[...]
Parameters:
  discordpongfnparamDBUSERParameter70CB30BD:
    Type: AWS::SSM::Parameter::Value<String>
    Default: fn-DB-USER

NodetsLayer

Similarly, a layer will be named and the source has to be in a folder layerName in src/layers/{layerName}/index.ts. Then a layer has to be referenced with import { someExport } from '@layer/layerName'. The aliasing for typescript is in tsconfig.json $.aliases and $.compilerOptions.paths.

Example in Discord authorizer layer:

export const verify = async (event: APIGatewayEvent): Promise<Boolean> => {
    ...
}

Can be referenced in the lambda function discrod-pong:

import { verify } from '@layer/discord-authorizer';

Explanations: During layer build, the layer is compiled into a module with a package.json file. At runtime this module will end up in the lambda filesystem inside the /nodejs/node_modules/@layer\/discord-authorizer. Thus when referencing '@layer/discord-authorizer` it will automatically find it.

Autotagging

The ResourceAspect will tag every Cloud Formation resource with whatever static tag given in the props:

const fn = new NodetsFunction(this, 'fn', {...});
Aspects.of(fn).add(new ResourceAspect({
  app: 'SampleApp'
}));

Will result in the template:

  fnreturn2005A3631C2:
    Type: AWS::Lambda::Function    
    Properties:
      # ...
      Tags:
        - Key: resource:type
          Value: AWS::Lambda::Function
        - Key: x-app
          Value: SampleApp

Any static tag is prefixed with x-. The aspect can also be applied to the App or Stack directly for recursive tagging. Some resource may be missed like the lambda for log retention in a lambda function.