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Postlight's Modern Serverless Starter Kit adds a light layer on top of the Serverless framework, giving you the latest in modern JavaScript (ES6 via Webpack, TypeScript if you want it, testing with Jest, linting with ESLint, and formatting with Prettier), the ease and power of Serverless, and a few handy helpers (like functions for handling warm functions and response helpers).

Once installed, you can create and deploy functions with the latest ES6 features in minutes, with linting and formatting baked in.

Read more about it in this handy introduction.

Note: Currently, this starter kit specifically targets AWS.

Install

# If you don't already have the serverless cli installed, do that
yarn global add serverless

# Use the serverless cli to install this repo
serverless install --url https://github.com/postlight/serverless-typescript-starter --name <your-service-name>

# cd into project and set it up
cd <your-service-name>

# Install dependencies
yarn install

Development

Creating and deploying a new function takes two steps, which you can see in action with this repo's default Hello World function (if you're already familiar with Serverless, you're probably familiar with these steps).

1. Add your function to `serverless.yml`

In the functions section of ./serverless.yml, you have to add your new function like so:

functions:
  hello:
    handler: src/hello.default
    events:
      - http:
          path: hello
          method: get

Ignoring the scheduling event, you can see here that we're setting up a function named hello with a handler at src/hello.ts (the .default piece is just indicating that the function to run will be the default export from that file). The http event says that this function will run when an http event is triggered (on AWS, this happens via API Gateway).

2. Create your function

This starter kit's Hello World function (which you will of course get rid of) can be found at ./src/hello.ts. There you can see a basic function that's intended to work in conjunction with API Gateway (i.e., it is web-accessible). Like most Serverless functions, the hello function is asynchronous and accepts an event & context. (This is all basic Serverless; if you've never used it, be sure to read through their docs.

You can develop and test your lambda functions locally in a few different ways.

Live-reloading functions

To run the hello function with the event data defined in fixtures/event.json (with live reloading), run:

yarn watch:hello

API Gateway-like local dev server

To spin up a local dev server that will more closely match the API Gateway endpoint/experience:

yarn serve

Test your functions with Jest

Jest is installed as the testrunner. To create a test, co-locate your test with the file it's testing as <filename>.test.ts and then run/watch tests with:

yarn test

Adding new functions/files to Webpack

When you add a new function to your serverless config, you don't need to also add it as a new entry for Webpack. The serverless-webpack plugin allows us to follow a simple convention in our serverless.yml file which is uses to automatically resolve your function handlers to the appropriate file:

functions:
  hello:
    handler: src/hello.default

As you can see, the path to the file with the function has to explicitly say where the handler file is. (If your function weren't the default export of that file, you'd do something like: src/hello.namedExport instead.)

Keep your lambda functions warm

Lambda functions will go "cold" if they haven't been invoked for a certain period of time (estimates vary, and AWS doesn't offer a clear answer). From the Serverless blog:

Cold start happens when you execute an inactive (cold) function for the first time. It occurs while your cloud provider provisions your selected runtime container and then runs your function. This process, referred to as cold start, will increase your execution time considerably.

A frequently running function won't have this problem, but you can keep your function running hot by scheduling a regular ping to your lambda function. Here's what that looks like in your serverless.yml:

custom:
  warmup:
    enabled: true
    events:
      - schedule: rate(5 minutes)
    prewarm: true
    concurrency: 2

The above config would keep all of your deployed lambda functions running warm. The prewarm flag will ensure your function is warmed immediately after deploys (so you don't have to wait five minutes for the first scheduled event). And by setting the concurrency to 2, we're keeping two instances warm for each deployed function.

Under custom.warmup, you can set project-wide warmup behaviors. On the other hand, if you want to set function-specific behaviours, you should use the warmup key under the select functions. You can browse all the options here.

Your handler function can then handle this event like so:

const myFunc = (event, context, callback) => {
  // Detect the keep-alive ping from CloudWatch and exit early. This keeps our
  // lambda function running hot.
  if (event.source === 'serverless-plugin-warmup') {
    // serverless-plugin-warmup is the source for Scheduled events
    return callback(null, 'pinged');
  }

  // ... the rest of your function
};

export default myFunc;

Copying and pasting the above can be tedious, so we've added a higher order function to wrap your run-warm functions. You still need to config the ping in your serverless.yml file; then your function should look like this:

import runWarm from './utils';

const myFunc = (event, context, callback) => {
  // Your function logic
};

export default runWarm(myFunc);

Pruning old versions of deployed functions

The Serverless framework doesn't purge previous versions of functions from AWS, so the number of previous versions can grow out of hand and eventually filling up your code storage. This starter kit includes serverless-prune-plugin which automatically prunes old versions from AWS. The config for this plugin can be found in serverless.yml file. The defaults are:

custom:
  prune:
    automatic: true
    number: 5 # Number of versions to keep

The above config removes all but the last five stale versions automatically after each deployment.

Go here for more on why pruning is useful.

Environment Variables

If you have environment variables stored in a .env file, you can reference them inside your serverless.yml and inside your functions. Considering you have a NAME variable:

In a function:

process.env.NAME

In serverless.yml:

provider:
  name: ${env:NAME}
  runtime: nodejs12.x

You can check the documentation here.

Deploy

Assuming you've already set up your default AWS credentials (or have set a different AWS profile via the profile field):

yarn deploy

yarn deploy will deploy to "dev" environment. You can deploy to stage or production with:

yarn deploy:stage

# -- or --

yarn deploy:production

After you've deployed, the output of the deploy script will give you the API endpoint for your deployed function(s), so you should be able to test the deployed API via that URL.

🔬 A Labs project from your friends at Postlight. Happy coding!

postlight/serverless-typescript-starter

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