AWS Lambda Layers Test

A simple project to test AWS Lambda functions & Layers written in TypeScript

Requirements

• Serverless framework
• npm install -g serverless

I just want to try it!

Open a terminal and run these commands:

• cd layers # enter the layers folder
• npm run build:all # install all dependencies and transpile TypeScript code into JS
• cd ../test-layer # enter the lambda function folder
• npm run first-start # install dependencies and run the lambda function locally using serverless offline plugin

Folder structure

• layers the folder that contains all layers:
  • express-pg-moment an example layer that bundles 3rd parties modules
    • ExpressJs
      • validator
      • cors
    • MomentJs
    • PostgreSQL client (pg)
    • Serverless HTTP
  • logging an example of a custom layer that logs messages
• test-layer a simple lambda function that uses the two layers listed above

Serverless Offline

To test the Lambda function locally just type:

• cd test-layer
• (npm install if you have just cloned the repo)
• npm run start
  • it simply calls sls offline start

Deploy Lambda function (with Serverless)

To deploy the lambda that uses the layers using serverless just type:

• cd test-layer
• npm run deploy -- --stage dev
  • it simply calls
    • npm install
    • sls deploy

Deploy Lambda Layers (with Serverless)

To deploy all layers using serverless just type:

• cd layers
• npm run deploy -- --stage dev it builds all layers, and it deploys them
  • it does the following for every layer:
    • npm run install
    • npm run build
  • it deploys all the layers
    • sls deploy

IMPORTANT NOTES

Layer export using CloudFormation notation

Layer must be exported wit TitleCase and LayerExport suffix: LoggingLayerExport

Layer name must be written with TitleCase and LambdaLayer suffix: LoggingLambdaLayer

in lambda layers serverless.yml:

sercice: layers
...
resources:
  Outputs:
    LoggingLayerExport:
      Value:
        Ref: LoggingLambdaLayer
      Export:
        Name: LoggingLambdaLayer-${self:provider.stage}

in lambda function serverless.yml:

functions:
  functionName:
    layers:
          - ${cf:layers-${self:provider.stage}.LoggingLayerExport}

where layers is the service name and LoggingLayerExport is the resource name

How to use layers locally

Function layers must be added in package.json as devDependencies, in this way won't be deployed. To prevent errors, custom dependencies must be excluded in the serverless.yml file

in package.json:

{
  "devDependencies": {
    "express": "^4.17.1",
    "logging": "file:../layers/logging/dist/nodejs/node_modules/logging"
  }
}

in serverless.yml:

package:
  exclude:
    - node_modules/logging

please note the difference from 3rd parties dependency (express) and custom dependency (logging)

• ExpressJS is just added to devDependencies
• Loggin is added to devDependencies and excluded in the package section

How to use typescript with layers (and how to decrease bundle size)

As the AWS Layers doc, a NodeJs layer is deployed on nodejs/node_modules folder. It's better to compile the TypeScript layer in Javascript and deploy only the compiled version.

This is why I've chosen the following folder structure for a layer written in TypeScript:

• logging the root folder
  • dist contains the compiled code (JavaScript) and follows the folder structure specified in the AWS documentation
    • nodejs
      • node_modules
        • logging
          • LAYER COMPILED CODE
  • src contains the source folder (TypeScript)
  • node_modules contains dependencies to compile and manage the deployment
  • package.jon contains scripts to compile and deploy the layer
  • tsconfig.json manage the compilation process

Only the content of the dist folder will be deployed, as configured in the path field in serverless.yml:

layers:
  logging:
    path: logging/dist
    description: Layer with a simple Logger
    compatibleRuntimes:
      - nodejs12.x

Useful lectures:

• Integrating Lambda Layers into your Node.js Lambdas using pre-configured templates
• NodeJS Runtime Environment with AWS Lambda Layers
• Lambda Layers & Node & require the layer code & sls invoke local
• How to deploy multiple micro-services under one API domain with Serverless
• How to use multiple runtimes in a single serverless microservice
• When to use Lambda Layers
• Get Started With AWS, Serverless, and TypeScript
• How I package TypeScript lambdas for AWS
• Part 2 — Create Lambda Layers with Serverless Framework and Offline support
• StackOverflow: Can I import typescript types from a Lambda Layer?
• Lambda Layers — Tips & Tricks
• Sharing Code among Lambdas using Lambda Layers

Videos

• Sharing Code with Lambda Layers
• Lambda Layers - Tips & Tricks
• How to use Lambda Layers with TypeScript