lerna-example

Illustrating the monorepo concept using lerna.

This tool has great benefits:

• Can manage recursive internal dependencies. Same logic for both internal and external dependencies, it's completely transparent.

• Ability to hoist common dependencies in 'master' lerna repo, this reduces complexity and build time.

• Run an npm command in a bulk lenra run on all subrepos or a filtered list (--scope flag) , can be parallelized (--parallel flag). See also lerna exec.

  This is great when dealing with microservices when needing to bring them all up or when needing to run tests for all of them.

• lerna import enables the import of an external git repository into the monorepo packages.

• Sophisticated npm package publishing based on many CI/CD scenarios using lerna publish and lerna version commands.

setup of a lerna monorepo from scratch

$ #first you have to install npx command runner gloablly (may need root user)
$ npm install -g npx

#install lerna as a dev dependency
$ npm init
$ npm i lerna --save-dev

$ #init monorepo config , this will create packages folder and lerna.json config
$ npx lerna init --independent

--independant flag means that each subrepo has its own npm versionning, there is also --exact mode : all of the subrepos follow the same versionning.

• You can customize lerna.json: yarn or npm as a package manager, projects tree, refine package publishing policy etc..

• Create your subrepo projects under packages folder. Each project under its own folder a it was a repository by itself.

Developer commands

It's preferrable to run commands from project root (where lerna.json resides)

• npx lerna bootstrap : The first command to launch. Must be ran when a subrepo is added/removed or after a fresh git clone. it links subrepos, installs npm deps and does some magic..

• npx lerna publish : publish to npm. Each time you publish, you will get a prompt for each package that has changed to specify if it's a patch, minor, major or custom change.

• npx lerna add <your local or remote package> : installs a package to all of the subrepos. when adding --scope=project-a for exemple this restricts to the given subrepo. Further doc

• npx lerna create <subrepo name> : adds a new subrepo.

Examples

• install lodash for project-a : npx lerna add lodash --scope=project-a

• install project-a as a dep for project-b : npx lerna add project-a --scope=project-b

The dependency schema in this sample monorepo is the following:

project-c -> | project-a | project-b -> project-a

Lerna with docker

base build image docker build . -f Dockerfilebase -t dependencies

then build service image:

docker build . -t project-c