The Problem

I run a small team working on a growing monorepo. Every commit, some CI checks run on the entire codebase, from GitHub actions. The checks were taking ~8 minutes to complete. We wanted them to run faster.

We use yarn workspaces to manage dependencies, so a single yarn install at root is enough to install the dependencies for all clients.

Trouble is, this yarn install was taking ~4.5 minutes on the CI. On my local machine, where the node modules have already been saved, this can take as little as 5 seconds. I wanted to speed up the CI.

The first thing I tried

GitHub actions recommends that you cache yarn’s cache. This means you end up with 2 steps that look like this:

- name: Get yarn cache directory path
  id: yarn-cache-dir-path
  run: echo "::set-output name=dir::$(yarn cache dir)"

- uses: actions/cache@v2
  id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)
  with:
    path: ${{ steps.yarn-cache-dir-path.outputs.dir }}
    key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
    restore-keys: |
      ${{ runner.os }}-yarn-

The first step grabs the yarn cache directory path, and saves it. The second step looks for anything stored in the cache, and restores it.

This sped things up a little, but it didn’t reach the heights I was hoping for.

The Solution

Instead of caching the yarn cache, you should cache your node_modules.

- uses: actions/cache@v2
  with:
    path: '**/node_modules'
    key: ${{ runner.os }}-modules-${{ hashFiles('**/yarn.lock') }}

This caches all of your node_modules folders throughout your repository, and busts the cache every time a yarn.lock file changes.

This works for our monorepo, and it should also work for single folder projects too.

This took our install step from ~4.5 minutes to ~30 seconds.

The Full Snippet

name: Automated Tests and Linting

on: [push]

jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v1

      - uses: actions/cache@v2
        with:
          path: '**/node_modules'
          key: ${{ runner.os }}-modules-${{ hashFiles('**/yarn.lock') }}

      - name: Install packages
        run: yarn install

      - name: Autogenerate GraphQL
        run: yarn codegen

      - name: Run Typescript Checks
        run: yarn lint

      - name: Run Tests
        run: yarn test:ci