example of workflow ci/cd for monorepo with github actions

workflow.yml

name: CI/CD Monorepo

env:
  AWS_REGION: us-east-1 # N. Virginia

on:
  push:
    branches:
      - main
    paths-ignore:
      - '**.md'

jobs:
  yarn:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        node-version: [12]

    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v2
        with:
          node-version: ${{ matrix.node-version }}
      - uses: actions/cache@v2
        name: yarn-cache
        id: yarn-cache
        with:
          path: |
            **/node_modules
            ${{ steps.yarn-cache-dir-path.outputs.dir }}
          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
          restore-keys: |
            ${{ runner.os }}-yarn
      - name: Yarn
        if: steps.yarn-cache.outputs.cache-hit != 'true'
        run: yarn install --frozen-lockfile --prefer-offline --non-interactive --ignore-scripts

  gatekeeper-server:
    runs-on: ubuntu-latest

    outputs:
      has-changed: ${{ steps.gatekeeper-cerberus.outputs.changed }}
    steps:
      - uses: actions/checkout@v2
        with:
          fetch-depth: 2
      - uses: marceloprado/has-changed-path@v1
        id: gatekeeper-cerberus
        with:
          paths: packages/server packages/utils packages/connectors packages/entities packages/events

  build-server:
    needs: [yarn, gatekeeper-server]
    if: needs.gatekeeper-cerberus.outputs.has-changed == 'true'
    runs-on: ubuntu-latest
    strategy:
      matrix:
        node-version: [12]

    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v2
        with:
          node-version: ${{ matrix.node-version }}
      - uses: actions/cache@v2
        name: yarn-cache
        id: yarn-cache
        with:
          path: |
            **/node_modules
            ${{ steps.yarn-cache-dir-path.outputs.dir }}
          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
          restore-keys: |
            ${{ runner.os }}-yarn
      - name: Build Server
        run: yarn workspace @monorepo/server build
      - name: Build Utils
        run: yarn workspace @monorepo/utils build
      - name: Build Connectors
        run: yarn workspace @monorepo/connectors build
      - name: Build Entities
        run: yarn workspace @monorepo/entities build
      - name: Build Events
        run: yarn workspace @monorepo/events build
      - name: Copy Dockerrun.aws.json
        run: |
          cp config/Dockerrun.aws.json Dockerrun.aws.json
      - name: Generate Deployment Package
        run: zip -r docker-multicontainer-v2.zip . --exclude '*.git*' '*node_modules*' '*.md' '*-web*' '*shared*' '*generators*'
      - name: Upload Deploy Zip Artifact
        uses: actions/upload-artifact@v2
        with:
          name: docker-multicontainer-v2.zip
          path: docker-multicontainer-v2.zip

  deploy-server:
    needs: [build-server]
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Download Deploy Zip Artifact
        uses: actions/download-artifact@v2
        with:
          name: docker-multicontainer-v2.zip
      - name: Configure AWS Credentials
        uses: aws-actions/configure-aws-credentials@v1
        with:
          aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
          aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
          aws-region: ${{ env.AWS_REGION }}
      - name: Get Current Date
        id: get_date
        run: echo "::set-output name=date::$(date +'%Y-%m-%d %H:%M:%S')"
      - name: Deploy Server to ELB
        uses: einaregilsson/beanstalk-deploy@v16
        with:
          aws_access_key: ${{ secrets.AWS_ACCESS_KEY_ID }}
          aws_secret_key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
          application_name: Awesome
          environment_name: Awesome-Staging
          region: ${{ env.AWS_REGION }}
          version_label: aewsome-staging-${{ steps.get_date.outputs.date }}-${{ github.run_id }}-${{ github.run_number }}
          version_description: awesome-server-build-${{ github.SHA }}
          deployment_package: docker-multicontainer-v2.zip
      - name: Deployed!
        run: echo Server Deployed to ELB

  gatekeeper-web-1:
    runs-on: ubuntu-latest

    outputs:
      has-changed: ${{ steps.gatekeeper-web-1.outputs.changed }}
    steps:
      - uses: actions/checkout@v2
        with:
          fetch-depth: 2
      - uses: marceloprado/has-changed-path@v1
        id: gatekeeper-deatheaters
        with:
          paths: packages/web-1 packages/shared packages/utils

  deploy-web-1:
    needs: [yarn, build-server, deploy-server, gatekeeper-web-1]
    if: |
      always() && 
      needs.gatekeeper-web-1.outputs.has-changed == 'true' && 
      (needs.build-server.result == 'success' || needs.build-server.result == 'skipped') &&
      (needs.deploy-server.result == 'success' || needs.deploy-server.result == 'skipped')
    runs-on: ubuntu-latest
    strategy:
      matrix:
        node-version: [12]

    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v2
        with:
          node-version: ${{ matrix.node-version }}
      - uses: actions/cache@v2
        name: yarn-cache
        id: yarn-cache
        with:
          path: |
            **/node_modules
            ${{ steps.yarn-cache-dir-path.outputs.dir }}
          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
          restore-keys: |
            ${{ runner.os }}-yarn-
      - name: Build Utils
        run: yarn workspace @monorepo/utils build
      - name: Build Web 1
        run: yarn workspace @monorepo/web-1 build
      - name: Configure AWS Credentials
        uses: aws-actions/configure-aws-credentials@v1
        with:
          aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
          aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
          aws-region: ${{ env.AWS_REGION }}
      - name: Deploy to S3 Bucket
        run: |
          cd packages/web-1/build
          aws s3 cp . s3://awesome-bucket --recursive --exclude '*.txt'
      - name: Invalidate Cache CloudFront
        run: |
          aws cloudfront create-invalidation --distribution-id ${{ secrets.CLOUDFRONT_WEB_1_ID }} --paths '/index.html'

  gatekeeper-web-2:
    runs-on: ubuntu-latest

    outputs:
      has-changed: ${{ steps.gatekeeper-web-2.outputs.changed }}
    steps:
      - uses: actions/checkout@v2
        with:
          fetch-depth: 2
      - uses: marceloprado/has-changed-path@v1
        id: gatekeeper-diagonalley
        with:
          paths: packages/web-2 packages/shared packages/utils

  deploy-web-2:
    runs-on: ubuntu-latest
    needs: [yarn, build-server, deploy-server, gatekeeper-web-2]
    if: |
      always() && 
      needs.gatekeeper-web-2.outputs.has-changed == 'true' &&
      (needs.build-server.result == 'success' || needs.build-server.result == 'skipped') &&
      (needs.deploy-server.result == 'success' || needs.deploy-server.result == 'skipped')
    strategy:
      matrix:
        node-version: [12]

    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v2
        with:
          node-version: ${{ matrix.node-version }}
      - uses: actions/cache@v2
        name: yarn-cache
        id: yarn-cache
        with:
          path: |
            **/node_modules
            ${{ steps.yarn-cache-dir-path.outputs.dir }}
          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
          restore-keys: |
            ${{ runner.os }}-yarn-
      - name: Build Utils
        run: yarn workspace @monorepo/utils build
      - name: Build Web 2
        run: yarn workspace @monorepo/web-2 build
      - name: Configure AWS Credentials
        uses: aws-actions/configure-aws-credentials@v1
        with:
          aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
          aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
          aws-region: ${{ env.AWS_REGION }}
      - name: Deploy to S3 Bucket
        run: |
          cd packages/web-2/build
          aws s3 cp . s3://awesome-bucket-url --recursive --exclude '*.txt'
      - name: Invalidate Cache CloudFront
        run: |
          aws cloudfront create-invalidation --distribution-id ${{ secrets.CLOUDFRONT_WEB_2_ID }} --paths '/index.html'

• cache dependencies
• deploy only if has changed
• deploy server to elastic beanstalk with docker multicontainer
• deploy web to s3
• invalidate web cache on cloudfront

It doesn't seem to be necessary to use matrix strategy if your matrix/array has one value given.