yarn-lock-to-package-json

A simple script to be used in Dockerfile to do yarn install without copying all package.jsons in a monorepo workspace. Use case inspired by pnpm's fetch command but for Yarn Berry.

Usage in Dockerfile

# ------------------------------------------------------------------------------
# First image (install dependencies)
# ------------------------------------------------------------------------------
FROM node:16-alpine as yarn
LABEL stage=yarn

WORKDIR /workspace

COPY .yarn ./.yarn
COPY yarn.lock .yarnrc.yml ./

RUN yarn dlx yarn-lock-to-package-json

RUN yarn install --immutable
# ------------------------------------------------------------------------------
# Server image (build image with production dependencies only)
# ------------------------------------------------------------------------------
FROM yarn as server
LABEL stage=server

WORKDIR /workspace

# Overwrite dummy package.json with actual ones (so that we can use scripts)
COPY package.json ./
COPY packages ./packages
COPY apps/server ./apps/server

RUN yarn workspaces foreach -tR --from @workspace-name/server run build

RUN cd apps/server && yarn workspaces focus --production

CMD ["yarn", "workspace", "@workspace-name/server", "start"]

Yarn Plugin

For similar functionality but packaged in a yarn plugin you can check out yarn-plugin-fetch by @devthejo, it uses this package internally to provide the same feature plus adds workspace focus support and more tools.

Working

What it does is parse the lockfile and recreate the monorepo structure by creating dummy package.json for each package in the workspace. These dummy package.json don't invalidate your docker cache when you change a script or increment a version and so your docker build cache remains valid up to the layer of RUN yarn install --immutable.

Test it by copying your yarn.lock to a new folder and run npx yarn-lock-to-package-json.

This is the dummy file generated:

{
  "name": "@monorepo/package",
  "version": "0.0.0",
  "description": "**DON'T COMMIT** Generated file for caching",
  "private": true,
  "dependencies": {
    "typescript": "^4.5.5"
  }
}

Motivation

These existing issues in yarn

• Install without package.json
• Fetch dependencies from yarn.lock only
• A command to just download and cache dependencies from lockfile