Vercel monorepo: install only a single project dependencies with Yarn
May 4, 2024
May 4, 2024
If you have a Vercel app as part of a monorepo, it may bother you that by default every build installs the whole monorepo dependencies.
If the Vercel app is the main project in the monorepo, it should go unnoticed, but if you have a bunch of other packages whose dependencies differ a lot from that of the Vercel app, then it will be very obvious that youâre spending a lot of time installing useless stuff on every build.
If youâre using a modern version of Yarn, aka not âYarn classicâ, aka
Yarn âBerryâ and later, which would be Yarn 4 today, then you can use
yarn workspaces focus to
do just that.
In Yarn 3, you need to
install the workspace-tools plugin via yarn plugin import workspace-tools for this to work. In Yarn 4, the command is supported
out of the box.
yarn workspaces focus, when run from inside a specific workspace
directory, will install that workspace dependencies, as well as the
dependencies of all the workspaces it depends on.
Note: if youâre using nodeLinker: node-modules, the node_modules
layout may differ a bit, especially the fact that packages from your
other workspaces are no longer installed at the root of the monorepo.
This will make it obvious if youâre implicitly depending on packages that are part of your monorepo but not depended on by your specific workspace.
In order to configure that on Vercel, you can configure the following in
vercel.json:
{
"installCommand": "yarn workspaces focus"
}
Note: youâll probably want to mirror that configuration inside your app settings in the Vercel dashboard in Settings > Build & Development Settings > Install Command, otherwise after you deploy, Vercel will warn you that âthe configuration of the current production deployment differ from your current project settingsâ.
Thereâs one more problem. Now you download only the dependencies of your project, which is much better, but on subsequent builds, Yarn keeps re-downloading everything again. Itâs like thereâs no cache!
Thatâs because Vercel and Yarn 3 and greater donât play well together.
Yarn needs its .yarn/cache and Vercel doesnât cache it between builds.
More details in this other post. đ
TLDR: use the following command.
{
"installCommand": "YARN_CACHE_FOLDER=.next/cache/yarn-cache yarn workspaces focus"
}