Sometimes you may want to run multiple applications that are using the same build image. In these cases, it may be more efficient to create a custom GitHub workflow that will build the image once and then deploy the applications from the same image. 
"on":
    push:
        branches:
            - main
env:
    PORTER_BASE_APP_NAME: base-app
    PORTER_BASE_IMAGE_REPOSITORY_URI: <base-image-repository-uri>
    PORTER_CLUSTER: <cluster-id>
    PORTER_DEPLOYMENT_TARGET_ID: <deployment-target-id>
    PORTER_HOST: https://dashboard.porter.run
    PORTER_PR_NUMBER: ${{ github.event.number }}
    PORTER_PROJECT: <project-id>
    PORTER_REPO_NAME: ${{ github.event.repository.name }}
    PORTER_TOKEN: ${{ secrets.<porter-token-secret-name> }}
jobs:
  build_image:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout Code
        uses: actions/checkout@v4

      - name: Setup Porter
        uses: porter-dev/setup-porter@v0.1.1

      - name: Build Image from Dockerfile
        run: exec porter app build $PORTER_BASE_APP_NAME --build-method docker --build-context . --dockerfile ./Dockerfile --tag $GITHUB_SHA

      - name: Push Image to Registry
        run: exec porter app push $PORTER_BASE_APP_NAME --tag $GITHUB_SHA

  deploy_apps:
    runs-on: ubuntu-latest
    needs: [build_image]
    strategy:
      matrix:
        app: ["base-app", "app-with-same-image-1", "app-with-same-image-2"]
    steps:
      - name: Checkout code
        uses: actions/checkout@v4

      - name: Setup Porter
        uses: porter-dev/setup-porter@v0.1.1

      - name: Deploy App
        run: exec porter app update ${{ matrix.app }} --image-repository $PORTER_BASE_IMAGE_REPOSITORY_URI --tag $GITHUB_SHA
To set up this workflow, you need to:
  1. Choose one of your applications to serve as the base application (PORTER_BASE_APP_NAME). The built images will be pushed to the repository for that application. You can choose any application with the shared build image.
  2. Get the repository URI for the base application and set PORTER_BASE_IMAGE_REPOSITORY_URI.
  3. Set the other fields including PORTER_CLUSTER, PORTER_PROJECT, PORTER_DEPLOYMENT_TARGET_ID, and PORTER_TOKEN. If you previously created a GitHub workflow for the base application, you should be able to use the same values.
  4. Update the deploy_apps job to include the names of the applications that will be deployed from the same image (deploy_apps.strategy.matrix.app).