Automating your package deployment in an Nx Monorepo with Changeset

All right, all right. I know, another monorepo package deployment post. But this was a pattern I didn't have luck finding with my Google Fu, and I figure that others may be interested in how to make an Nx workspace work with the changesets package.

If you haven't heard of Nx, it's a monorepo build framework that helps keep your build, test, and run scripts ini the same format while having different actions, along with being smart enough to determine what has and hasn't been affected since your last changes.

Changesets on the other hand is a semver version management tool that integrates well with pnpm and yarn workspaces by looking at the workspace file and walking you through a wizard for setting up which packages have changed (and has a great GitHub Actions integration and bot for previewing which packages will be updated and how).

Now that these are defined, onto the meat of those post.

So what's the problem?

I migrated from using a pnpm workspace to using Nx with pnpm workspaces so that I could take advantage of running all of my commands through Nx and get some sweet caching of my commands and familiarity between all of the commands. So now instead of having to try to remember "Is it pnpm -r build?" and the "How do I filter to only some of the projects again?", I only have to remember pnpm nx build <project> or pnpm nx --run-many build --all. I promise, these commands start rolling off your fingers as you keep using them.

Now, with my pnpm workspace, every package was built in a dist directory right next to the src so I'd have packages/<package>/src and packages/<package>/dist and I could easily keep a package.json per package and have it deploy from right there. With Nx, that's not really the case anymore. There's a root package.json that holds all of the dependencies and most of the time, the outDir is set to be <workspaceRoot>/dist/<package>/src. Kind of makes deploying from a central location just a bit harder.

For the build command with Nx, I'm actually using the @nrwl/node:package executor, which runs a build command via tsc and copies over the package.json (if you have one), and sets it up with the proper path for publishing, and copies the package's README and CHANGELOG if they exist. If you don't have a package.json for the library, Nx will create one for you and populate it with the dependencies it finds in the compiled code. You can set the outputPath to anything you want, but I've found that dist/<package> works really well for this automation setup. You could actually do packages/<package>, but then your ts and your js will get mixed with each other, which I find very messy and confusing.

So now why is having these packages in the dist/ directory a problem? Well, because changesets works by reading the workspace's configuration, and as we want to have our source code version tracked, but not the compiled code, we don't normally include the dist in our git repository. Because of this, when we do things like pnpm changeset to create a new changeset, we'll eventually be modifying the package.json in the packages/<package>/ directory.

The changeset action that I mentioned earlier works like this during your CI workflow:

1. check if there's one or more changeset file(s)
   1. if yes, open a PR with the updates to the appropriate package.jsons (in the packages/<package> directories)
   2. if no, check that the packages in the workspace configuration are all up to date
      1. if no, run the publish action to update npm with the most recent package version

Something to note is that when the package.json for a specific package, that package will then be picked up by nx affected meaning that you can only build the packages that will be published in CI if you feel up to going that route.

So a typical workflow would look something like

1. git pull
2. git checkout -b
3. make changes
4. commit changes as often as you normally would
5. pnpm changeset
6. follow the changeset wizard and set up the changes to be made
7. git add .
8. git commit
9. git push origin
10. merge PR
11. let the changeset action make a new version PR
12. review and merge
13. let changeset publish

The final problem occurs in this "let changeset publish" step, and the solution is coming up.

Modifying the workspace file only in CI

So after playing with ideas of using different tools, manual workflows, I finally came to a solution that works well using some bash scripting in CI. For me, my pnpm-workspace.yaml file usually looks something like

packages:
  - 'packages/**

and I realized that with the sed tool I would be able to change that packages/** to dist/** only during CI so that the changeset publish command would look in the correct directory for the packages I want to publish. So now the actions file looks something like this:

name: Release

on:
  push:
    branches:
      - main

env:
  NX_BRANCH: ${{ github.event.pull_request.head.ref }}
  NX_RUN_GROUP: ${{ github.run_id }}
  NX_CLOUD_DISTRIBUTED_EXECUTION: true
  NX_CLOUD_AUTH_TOKEN: ${{ secrets.NX_CLOUD_TOKEN }}

jobs:
  release:
    name: Release
    runs-on: ubuntu-latest
    steps:
      - name: Checkout Repo
        uses: actions/checkout@master
        with:
          # This makes Actions fetch all Git history so that Changesets can generate changelogs with the correct commits
          fetch-depth: 0
      - name: Derive appropriate SHAs for base and head for `nx affected` commands
        uses: nrwl/nx-set-shas@v1

      - name: Setup Node.js 14.x
        uses: actions/setup-node@master
        with:
          node-version: 14.x

      - name: Install pnpm
        run: npm i -g pnpm

      - name: Install Dependencies
        run: pnpm i --frozen-lockfile=false

      - name: Build Projects
        run: pnpm build

      - name: Modify Workspace File
        run: sed -e "s|'packages\/|'dist/|" pnpm-workspace.yaml > pnpm-new.yaml && mv pnpm-new.yaml pnpm-workspace.yaml

      - name: Create Release Pull Request or Publish to npm
        id: changesets
        uses: changesets/action@master
        with:
          # This expects you to have a script called release which does a build for your packages and calls changeset publish
          publish: pnpm release
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          NPM_TOKEN: ${{ secrets.NPM_TOKEN }}

      - name: Stop Nx Cloud Agents
        run: pnpx -y nx-cloud stop-all-agents

  nx_agent:
    runs-on: ubuntu-latest
    name: Nx Agent
    timeout-minutes: 60
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v1
        with:
          node-version: 14.x
      - name: Install pnpm
        run: npm i -g pnpm

      - name: Install Dependencies
        run: pnpm i --frozen-lockfile=false
      - run: pnpx nx-cloud start-agent

Normally, I'd use the -i option for sed, to write in place, but that's not an option on GitHub Action Runners, so writing to a temp file and overwriting the original file works instead.

So now, what's happening is that when a PR is made with a changeset (or multiple changesets) a second PR will be automatically opened by the changeset action to update bump the package versions and generate the CHANGELOG files based on the changesets being merged in. Then, when that PR gets merged, Nx will see what packages have been modified, build them to the dist/<package> directory, copying over the package.json, README, and CHANGELOG. Now our custom sed script will rewrite the pnpm-workspace.yml so that we point changesets to the correct directory for the to-be-published packages. Changesets will then see what packages are there, what is public, and what has mismatched versions compared to what's on the npm registry, and publish whatever is missing so that it's all up to date. Also, a GitHub release will be created during this too, so you have a tag and release pointing to the repo at that point in time.

Overall, I'm pretty excited to have this flow automated and working through three of my favorite package management tools. Everything will also work if you're using a yarn workspace instead, just change the sed script to modify the workspace file for yarn instead of the one for pnpm. I'm currently using this for my ogma and nest-commander repositories, feel free to have a look if you need some inspiration and/or real life examples. If you're developing packages and using an Nx workspace and need automated package deployment, give this a shot.

A side note that I just ran into: if you have workspace in your package.json because you changed from yarn to pnpm or some similar reason, make sure to remove it, or the above workflow will no longer work as expected.