Migrating to Yarn 2
Last updated June 01, 2021
Table of Contents
To our excitement, Yarn 2 was released in early 2020. The team has created a “zero downloads” package manager, which means users may use “vendor” directories to include their yarn binaries, dependencies, and development dependencies in their repositories. Learn more about Yarn’s new philosophy.
This article is intended to help current Heroku users migrate from Yarn 1 to Yarn 2. Apps being migrated should already be using Yarn 1 and are using the most up-to-date version of the Heroku Node.js buildpack. This article will not work for applications that install Yarn from other scripts, such as the Heroku Ruby buildpack. Heroku expects all dependencies to be included in the
.yarn directory to take full advantage of “zero downloads”.
Heroku users using Yarn are not required to migrate to Yarn 2, and users will have access to Yarn 1 in their apps after it is deprecated. However, it’s advised to migrate to Yarn 2 to ensure the most up-to-date bug fixes and security patches in the package manager.
Use this article to migrate your app code locally to Yarn 2, as well your application on Heroku.
The following will reference checking files into
git while directions could also be applied to other version control systems.
Prepare local environment
Enter the directory of the source code that needs the migration. The local commands will be run at the root of the project. Make sure the local yarn version is up to date. To update it locally, run install with npm:
npm install -g yarn
The version should be
>= 1.22.4. Run
yarn -v to confirm.
Move custom cache directories to workspaces
package.json, change your
workspaces. For example, if you have the following:
"cacheDirectories": [ "client/node_modules" ]
Change it to the following, and specify that the project is private:
"workspaces": [ "client" ], "private": true,
There’s no need to specify the
node_modules directory. Make sure the
"name" key in the
package.json of the subdirectory reflects the directory name and the workspace name specified in the root
Next, delete any
node_modules folders and
yarn.lock files in subdirectories, and go to your application directory and run
cd ~/path/to/project && yarn install
This should update the
yarn.lock file of your directory to reflect the entire dependency tree specified by the workspaces. Confirm that the lock file has been updated by looking for a dependency that has been specified in a
package.json of a subdirectory.
Make changes to source code
There are additional files that must be checked into git in order to use Yarn 2 on Heroku. Yarn subscribes to a “zero-download” philosophy. There will be additional download costs to checking into git more files and directories, but this will create faster builds on Heroku.
yarn to set the yarn version on the source code.
yarn set version berry
This will create a
.yarnrc.yml file and a
.yarn directory. Check both into git and make sure they are available to Heroku at build time. In the
.yarn directory, there is a
releases directory that contains a
Next, install the dependencies from the
yarn.lock file will be modified. Check these changes into git.
Add the following to your
.yarn/* !.yarn/cache !.yarn/releases !.yarn/plugins !.yarn/sdks !.yarn/versions
pnp.js file is also generated - this is the “Plug N Play” file. Yarn uses it to access the packages. There are also additional directories that are generated in the
.yarn directory, including a new directory
cache where dependencies are installed. Check the tracked contents of
.yarn into git.
The contents of
.yarn/cache are not comparable to
node_modules. The files are compressed and are meant to be checked into the project.
Clear Heroku App cache
Since Heroku won’t be restoring the cache at the beginning of the build or storing it at the end of the build, you can go ahead and purge any build cache that is leftover from previous builds.
Make sure you have
heroku-cli installed. Then, install the
heroku plugins:install heroku-builds
Next, run the command to clear the cache.
heroku builds:cache:purge --app $APP_NAME
After this, you’ll want to redeploy your app, but first finish up the next steps to ensure a successful deploy.
Update Heroku environment (with Plug'n'Play)
If you’re using Yarn 2, you have the option of using Yarn’s Plug'n'Play to reference dependencies, or you can continue to use node modules. Each requires a slightly different set up, so if you intend to use node modules, set up your app accordingly.
Disable dependency caching
Right now, Heroku doesn’t cache dependencies with Yarn 2 from the
.yarn/cache directory. When using Plug'n'Play, Yarn will expect zipped up dependencies to be in the
.yarn/cache directory. However, the buildpack will still run
yarn install to ensure that
postinstall scripts will be run for all dependencies.
You will want to remove the environment variables that are associated with Yarn 1 and
node_modules. Therefore, remove the
NODE_MODULES_CACHE environment variable. This variable should be set to
heroku config:set NODE_MODULES_CACHE=false
Heroku is working on caching from the
.yarn/cache directory, but it is not supported yet. If you’d like to use a custom cache setup, you can do with custom caching configuration.
Remove private registry environment variables
If you’ve set any tokens for accessing a private registry and you’re using Yarn 2 with a checked in cache, unset those as well. You may do something like this:
heroku config:unset PRIVATE_NPM_TOKEN
Update Heroku environment (for node modules)
As described above, you will either be using Plug'n'Play or node modules for dependencies. To use Plug'n'Play, you’ll want to follow the instructions above.
Set up Yarn configuration
If you’ve opted out of using PnP for dependencies, you’ll need to specify this in your
.yarnrc.yml. Add the following:
There’s more customizable Yarn 2 configurations documented here.
Now you’re ready to use node modules with Yarn 2!
If you’re using node modules, it’s up to you if you want to use the Heroku cache to store dependencies between builds. It’s advised to test which provides a more performant and secure build for your app.
If you are already caching dependencies, test your app with the cache turned off.
heroku config:set NODE_MODULES_CACHE=false
To reenable the cache, reset the
heroku config:set NODE_MODULES_CACHE=true
The Yarn 2 package manager is modularized, so you’ll have to install the workspaces plugin in order to prune out devDependencies. This is suggested because the Node.js runtime will not need devDependencies installed, so it’s preferred to remove them after the build is complete so that they are not compiled into the slug.
In order to install, run the following:
yarn plugin import workspaces-tools
Check in all the created artifacts into git with the other files that have been generated to use Yarn in the .yarn file.
Test your App
After you’ve made your changes, make sure to run your test suite on your app’s code. Once the tests have passed successfully, deploy your application to Heroku. Confirm that the build has been successful.
If you run into any issues, please open an Issue on GitHub.