Lerna

May 4, 2020

nodejs, docker, expressjs, lerna, monorepo

Monorepo (all projects are stored in a single repository) is a relatively new concept (to me) and so I’ve provided more than usual hits/sample code in the kata. This is primarily to help me cement the core commands.

The BACKGROUND to why I’ve created this is kata is this. I’ve recently needed to create several RabbitMQ consumers through a devised pattern, including additional common functionality. As there is common code, I did not want to violate the DRY principle so set about researching a way to do this, easily, with a nodejs repo. As these consumers, plus additional functionality, are small, I felt it UNNECESSARY to create a layer of complexity that would have come about if I were to have gone down the multiple repository route as well as having a private npm registry for the common code. THANKFULLY I found Lerna and Lerna fits my requirements perfectly.

Requirements

Create a new lerna project:

$ mkdir lerna-kata && cd lerna-kata
$ npm i lerna
$ lerna init

Create a new package called @kata/web:

$ lerna create @kata/web -y

Add these sections into packages/web/package.json:

  "script" : {
      "start": "node lib/web.js"
  },
  "dependencies": {    
      "express": "^4.17.1"
  }

Cut & Paste and overwrite in packages/web/lib/web.js:

const common = require('@kata/common')
const express = require('express')
const app = express()
const router = express.Router()
const http = require('http').createServer(app)
const port = process.env.PORT || 3000
router.get('/', async (req, res) => {
    res.status(200).send(common.getMessage())
})

app.use('/', router)

http.listen(port, () => {
    console.log(`Connected, listening on port: ${port}`)
})

Create a new package called @kata/common:

$ lerna create @kata/common -y

Add these sections into packages/common.package.json:

  "script" : {
      "start": "node lib/common.js"
  }
  "dependencies": {    
      "moment": "^2.25.2"
  }

Cut & Paste and overwrite in packages/common/lib/common.js

const moment = require('moment')
const started = moment(Date.now())
const getMessage = () => {
    return `Web started ${moment(Date.now()).diff(started, "seconds")} seconds ago`
}
module.exports = {
    getMessage
}

Add @kata/common reference to @kata/web
Configure root package.json to bootstrap project dependencies
Configure root package.json to start all projects
Configure root package.json to stream logs
Now run
Set version in all packages:

$ git add .
$ git commit -m "chore(release): set version"
$ lerna version --no-push --conventional-commits --no-changelog

info cli using local version of lerna
lerna notice cli v3.20.2
lerna info current version 0.0.4
lerna info Looking for changed packages since v0.0.4
lerna info getChangelogConfig Successfully resolved preset "conventional-changelog-angular"

Changes:
 - @kata/common: 0.0.4 => 0.0.5
 - @kata/web: 0.0.4 => 0.0.5

? Are you sure you want to create these versions? Yes
lerna info execute Skipping git push
lerna info execute Skipping releases
lerna success version finished

Advanced 1 - scoped project

Start a scoped project
Create Dockerfile & run

Advanced 2 - import

Import existing repository

$ lerna import <local git repository> --dest=src

src above ^^^ must also be listed in the list of packages in the <root>/lerna.json file:

"packages": ["packages/*","src/*"]

Tech

nodejs
lerna
docker

References

Hints

Hint 1 - initial setup

$ mkdir lerna-kata && cd lerna-kata
$ npm i lerna
$ lerna init
$ lerna create @kata/web -y
$ lerna create @kata/common -y

Hint 2 - bootstrap & run

To bootstrap all packages AND just have one shared node_modules folder, OR to start all projects (not scoped to a specific package), add this to <root>/package.js:

"scripts": {
    "bootstrap": "lerna clean && lerna bootstrap --hoist",
    "start": "lerna run start --stream"
}

Hint 3 - add package reference

To add a reference from one project to another, run:

$ lerna add @kata/common --scope @kata/web

Hint 4 - install dependencies

To bootstrap all dependencies, run:

$ cd <root>
$ npm run bootstrap

Hint 5 - run

To run:

$ cd <root>
$ npm run start
$ curl -X GET localhost:3000

To access root web page:

Linux

run:

$ curl -X GET http://localhost:3000
Web started 654 seconds ago

Windows

run:

$ curl http://localhost:3000 -UseBasicParsing

StatusCode        : 200
StatusDescription : OK
Content           : Web started 483 seconds ago
RawContent        : HTTP/1.1 200 OK
                    Connection: keep-alive
                    Content-Length: 27
                    Content-Type: text/html; charset=utf-8
                    ETag: W/"1b-499fpsrG7b9xfw5MwAIxMn33THg"
                    X-Powered-By: Expres...
Forms             :
Headers           : {[Connection, keep-alive], [Content-Length, 27], [Content-Type, text/html; charset=utf-8], [Date, Mon, 04 May
                    2020 14:34:31 GMT]...}
Images            : {}
InputFields       : {}
Links             : {}
ParsedHtml        :
RawContentLength  : 27