lerna-docker

Streamline building Docker containers from lerna monorepo projects.

When To Use lerna-docker

lerna-docker solves a bit of a niche problem, albeit a frustrating one. If you:

• Are using lerna.
• Have multiple deployable projects that depend on common packages.
• Need those deployable projects built into Docker containers.
• Want to only build those deployable projects when there are changes to it or it's dependencies.

...this is the library for you

Usage

There are multiple ways to use lerna-docker but you'll most likely use it within CI in some fashion.

As An NPM Package

yarn add @halfmatthalfcat/lerna-docker

or

npm i @halfmatthalfcat/lerna-docker

After installing into your project, you can either add a script into your package.json and call lerna-docker from there or you can call ./node_modules/@halfmatthalfcat/lerna-docker/index.js directly.

As A Github Action

lerna-docker comes out-of-the-box as a Github Action however, you still must install it into your project as a dev dependency. This is mostly to avoid committing node_modules into this repo. To use it in a Github Workflow, can do the following:

jobs:
  build:
    steps:
      # all your usual build steps
      - name: Dockerize
        uses: ./node_modules/@halfmatthalfcat/lerna-docker
        env:
          # any/all the configuration options

Configuration

Variable	Required	Description
VERSION_PREFIX	X	The SemVer prerelease prefix (rc, dev, pr)
VERSION_PRERELEASE		The SemVer prerelease to "force"
GIT_EMAIL	X	The git email to use when tagging
GIT_USERNAME	X	The git username to use when tagging
DOCKER_REGISTRY	X	The docker registry to publish to
DOCKER_REGISTRY_USERNAME		An optional username to use when auth-ing against a docker registry
DOCKER_REGISTRY_PASSWORD		An optional password to use when auth-ing against a docker registry
DOCKER_IMAGE_PREFIX		An optional docker image prefix to use in the final image path
DOCKER_BUILD_ARG_*		Optional build args to use when building
DOCKER_LABEL_*		Optional image labels to attach when building

How lerna-docker Works

There are certain requirements/concessions necessary in order for lerna-docker to work.

1. You are already using lerna.
   1. You technically don't have to be using lerna, however a properly configured lerna.json file at the root of your project is necessary.
2. You have a top-level /docker directory that contains Dockerfiles for the projects which require containerizing.
   1. The Dockerfiles should directly map to the package name. Packages that do not have an associated Dockerfile will not be built.
3. You are comfortable with a time-based SemVer tag pattern (year.month.date).

High Level Flow

1. Changes are made to the repository to any or all dependencies.
2. Those changes are pushed to the origin.
3. lerna changed is ran to determine which packages changed from the previous tag.
4. If any packages that have changed have an associated Dockerfile under /docker, that Dockerfile is built against the root of the project.
5. A new SemVer tag is created based on the current date and current build against the trunk.
6. The container(s) are pushed to their respective registries.
7. The created tag is push to the origin.
   1. This is a manual step done by the pipeline after successful pushes

Example

Consider the following directory structure:

project_root/
├─ docker/
│  ├─ user_service.Dockerfile/
│  ├─ auth_service.Dockerfile/
├─ packages/
│  ├─ common/
│  ├─ models/
│  │  ├─ dependencies: common
│  ├─ user_service/
│  │  ├─ dependencies: common, models
│  ├─ auth_service/
│  │  ├─ dependencies: common, models
├─ .dockerignore
├─ lerna.json

We have four packages (common, models, user_service and auth_service) that all have various dependencies on each other. We want to deploy user_service and auth_service both independently and if/when their dependencies on other packages change.

Changes to auth_service

Direct changes to auth_service will trigger a build of auth_service alone during CI. A new container of auth_service will be created with the latest tag and pushed to the registry.

Changes to models

Both auth_service and user_service have dependencies on models and thus, will be built, tagged with the latest version and pushed to the registry.

Changes to common

Since everything is dependent on common, everything has "changed". However, models does not have an associated Dockerfile under /docker, so no container will be built for models however, containers will be built, tagged and pushed for user_service and auth_service.

Versioning

lerna-docker takes an opinionated approach to versioning. The primary reasoning behind this is traditional major.minor.patch versioning is difficult in a monorepo. How do we decide what to bump when? Projects like Conventional Commits try to accomplish this through commit messages however lerna-docker strives to streamline this process.

Because of this, it's probably less appropriate to use lerna-docker for packaging libraries that need to abide by major.minor.patch to telegraph actual changes to the project.

The versioning for lerna-docker operates as so:

{year}.         - the current year
{month}.        - the current month
{day}.          - the current day
-{prefix}.      - a user-defined prerelease prefix (rc, dev, pr)
{prerelease}    - a prerelease version (automatic or manual)

Imagine it's the first day of the year and we've designated builds against main to hold the prefix rc, for release candidate. The resulting first version of the first commit on main would be 2023.1.1-rc.0.

Any subsequent builds for that day would increment the rc version monotonically. The value would reset to 0 on the following day.

Now let's imagine we want to build containers for each commit of a pull request. For this we'll designate the prefix to be pr. We can manually define the prerelease version (as an environment variable) instead of letting lerna-docker manually increment one. For example, we could use the Pull Request number and Workflow run as our prerelease, resulting in a tag such as 2023.1.1-pr.22.53. The prerelease value should be a valid SemVer prerelease value.