Can't use yarn in subdirectory

[rugged girder]

I'm trying to deploy a monorepo (/client + /server) from a single service.

My build command is: cd client && yarn run build && cd ../server && yarn run build

My deployments are failing with the error message: /bin/bash: line 1: yarn: command not found

I think this is because Railway only installs yarn if a yarn.lock file is found in the root directory. In this case, I have yarn.lock files in the app subdirectories, but not the root directory.

Is there a way to force yarn to be used for my service? Or is the issue something else?

[lofty dust]

You can force yarn by setting NIXPACKS_PKGS=yarn but it'd be better if you run client and server as two separate services.