Use variable to change machine type in Cloud Build

Question

In cloud build trigger I created a variable: key _MACHINE_TYPE value: E2_HIGHCPU_8

I set this variable in my cloudbuild.yaml:

 steps:
  # Build Backend image and push with kaniko
  - name: 'gcr.io/kaniko-project/executor:latest'
    id: '[Backend] Build & Push image'
    args:
      - --dockerfile=backend/Dockerfile
      - --destination=$_BACKEND_IMAGE_REPO:$_APP_VERSION
      - --destination=$_BACKEND_IMAGE_REPO:$_PROJECT
      - --cache=true
      - --build-arg=user=user
      - --build-arg=uid=1000
      - --context=/workspace/backend
      - --target=production

  # Build Frontend image and push with kaniko
  - name: 'gcr.io/kaniko-project/executor:latest'
    id: '[Frontend] Build & Push image'
    args:
      - --dockerfile=frontend/Dockerfile
      - --destination=$_FRONTEND_IMAGE_REPO:$_APP_VERSION
      - --destination=$_FRONTEND_IMAGE_REPO:$_PROJECT
      - --cache=true
      - --build-arg=REACT_APP_VERSION=$_APP_VERSION
      - --build-arg=REACT_APP_WEBSITE_NAME=$_WEBSITE_NAME
      - --build-arg=REACT_APP_BACKEND_BASE_URL=$_BACKEND_URL
      - --build-arg=REACT_APP_GOOGLE_MAP_KEY=$_GOOGLE_MAP_KEY
      - --context=/workspace/frontend
      - --target=production

  # Laravel Migration
  - name: 'gcr.io/google-appengine/exec-wrapper'
    id: 'Laravel Migration'
    args: [
      '-i', $_BACKEND_IMAGE_REPO:$_PROJECT,
      '-e', 'DB_CONNECTION=$_DB_CONNECTION',
      '-e', 'DB_SOCKET=$_DB_SOCKET',
      '-e', 'DB_PORT=$_DB_PORT',
      '-e', 'DB_DATABASE=$_DB_DATABASE',
      '-e', 'DB_USERNAME=$_DB_USERNAME',
      '-e', 'DB_PASSWORD=$_DB_PASSWORD',
      '-s', $_DB_INSTANCE_NAME,
      '--', 'scripts/migration.sh', '--config=$_MIGRATION_CONFIG'
    ]
    waitFor:
      - '[Backend] Build & Push image'
      - '[Frontend] Build & Push image'

 # Deploy Backend image to Cloud Run
  - name: 'gcr.io/google.com/cloudsdktool/cloud-sdk'
    id: '[Backend] Cloud Run Deployment'
    entrypoint: gcloud
    args: [
      'run', 'deploy', '$_BACKEND_SERVICE_NAME',
      '--image', '$_BACKEND_IMAGE_REPO:$_PROJECT', 
      '--region', '$_REGION',
      '--update-env-vars', 'APP_VERSION=$TAG_NAME'
    ]
    waitFor:
      - '[Backend] Build & Push image'
      - '[Frontend] Build & Push image'
      - 'Laravel Migration'

  # Deploy Frontend image to Cloud Run
  - name: 'gcr.io/google.com/cloudsdktool/cloud-sdk'
    id: '[Frontend] Cloud Run Deployment'
    entrypoint: gcloud
    args: [
      'run', 'deploy', '$_FRONTEND_SERVICE_NAME',
      '--image', '$_FRONTEND_IMAGE_REPO:$_PROJECT',
      '--region', '$_REGION'
    ]
    waitFor:
      - '[Backend] Build & Push image'
      - '[Frontend] Build & Push image'
      - 'Laravel Migration'
      - '[Backend] Cloud Run Deployment'

  # Deploy Cloud Scheduler Crons
  - name: 'gcr.io/google.com/cloudsdktool/cloud-sdk'
    id: 'Deploy Cloud Scheduler Crons'
    env:
      - 'PROJECT_ID=$PROJECT_ID'
      - 'PROJECT=$_PROJECT'
      - 'REGION=$_REGION'
      - 'BACKEND_URL=$_BACKEND_URL'
      - 'TASK_MANAGER_TOKEN=$_TASK_MANAGER_TOKEN'
      - 'TASK_PAUSE=$_TASK_PAUSE'
    entrypoint: 'bash'
    args: ['./create-crons.sh']

 options:
  dynamic_substitutions: true
  substitution_option: 'ALLOW_LOOSE'
  machineType: $_MACHINE_TYPE
 timeout: 3600s

But I have this error when I start my pipeline:

failed unmarshalling build config cloudbuild.yaml: unknown value "\"$_MACHINE_TYPE\"" for enum google.devtools.cloudbuild.v1.BuildOptions.MachineType`

How can I use a variable to change the machine type with a substitution ?

Answer 1

The Substituting variable values documentation states that, Use substitutions in your build's steps and images to resolve their values at build time. So, variable substitutions are only available for use within these two steps. The BuildOptions object would be a different object and therefore it is not qualified for this type of variable substitution.

If you really need to use variable substitution, consider using the gcloud builds submit command line instead, then call it with the --machine-type flag.