Allow scaling with Deployments directly

app/actions/deployment_create.rb

@@ -43,6 +43,8 @@ def create(app:, user_audit_info:, message:)
 
           desired_instances = desired_instances(app.oldest_web_process, previous_deployment)
 
+          validate_quota!(message, app)
+
           deployment = DeploymentModel.create(
             app: app,
             state: starting_state(message),
@@ -55,7 +57,8 @@ def create(app:, user_audit_info:, message:)
             revision_version: revision&.version,
             strategy: message.strategy,
             max_in_flight: message.max_in_flight,
-            canary_steps: message.options&.dig(:canary, :steps)
+            canary_steps: message.options&.dig(:canary, :steps),
+            web_instances: message.web_instances || desired_instances
           )
 
           MetadataUpdate.update(deployment, message)
@@ -163,7 +166,21 @@ def record_audit_event(deployment, droplet, user_audit_info, message)
 
       private
 
+      def validate_quota!(message, app)
+        return if message.web_instances.blank?
+
+        current_web_process = app.newest_web_process
+        current_web_process.instances = message.web_instances
+
+        current_web_process.validate
+
+        raise Sequel::ValidationFailed.new(current_web_process) unless current_web_process.valid?
+
+        current_web_process.reload
+      end
+
       def deployment_for_stopped_app(app, message, previous_deployment, previous_droplet, revision, target_state, user_audit_info)
+        app.newest_web_process.update(instances: message.web_instances) if message.web_instances
         # Do not create a revision here because AppStart will not handle the rollback case
         AppStart.start(app: app, user_audit_info: user_audit_info, create_revision: false)
 
@@ -179,7 +196,8 @@ def deployment_for_stopped_app(app, message, previous_deployment, previous_dropl
           revision_version: revision&.version,
           strategy: message.strategy,
           max_in_flight: message.max_in_flight,
-          canary_steps: message.options&.dig(:canary, :steps)
+          canary_steps: message.options&.dig(:canary, :steps),
+          web_instances: message.web_instances || desired_instances(app.oldest_web_process, previous_deployment)
         )
 
         MetadataUpdate.update(deployment, message)
@@ -223,6 +241,8 @@ def starting_state(message)
       def starting_process_instances(deployment, desired_instances)
         starting_process_count = if deployment.strategy == DeploymentModel::CANARY_STRATEGY
                                    deployment.canary_step[:canary]
+                                 elsif deployment.web_instances
+                                   deployment.web_instances
                                  else
                                    desired_instances
                                  end

app/messages/deployment_create_message.rb

@@ -13,6 +13,7 @@ class DeploymentCreateMessage < MetadataBaseMessage
     ALLOWED_OPTION_KEYS = %i[
       canary
       max_in_flight
+      web_instances
     ].freeze
 
     ALLOWED_STEP_KEYS = [
@@ -43,6 +44,10 @@ def max_in_flight
       options&.dig(:max_in_flight) || 1
     end
 
+    def web_instances
+      options&.dig(:web_instances)
+    end
+
     private
 
     def mutually_exclusive_droplet_sources
@@ -62,6 +67,7 @@ def validate_options
       disallowed_keys = options.keys - ALLOWED_OPTION_KEYS
       errors.add(:options, "has unsupported key(s): #{disallowed_keys.join(', ')}") if disallowed_keys.present?
 
+      validate_web_instances if options[:web_instances]
       validate_max_in_flight if options[:max_in_flight]
       validate_canary if options[:canary]
     end
@@ -74,6 +80,14 @@ def validate_max_in_flight
       errors.add(:max_in_flight, 'must be an integer greater than 0')
     end
 
+    def validate_web_instances
+      web_instances = options[:web_instances]
+
+      return unless !web_instances.is_a?(Integer) || web_instances < 1
+
+      errors.add(:web_instances, 'must be an integer greater than 0')
+    end
+
     def validate_canary
       canary_options = options[:canary]
       unless canary_options.is_a?(Hash)

app/models/runtime/deployment_model.rb

@@ -113,6 +113,14 @@ def continuable?
       state == DeploymentModel::PAUSED_STATE
     end
 
+    def desired_web_instances
+      # It seems redundant to have method since web_instances defaults to original_web_process_instance_count,
+      # (in deployment create action)
+      # but this should handle deployments created on old API vms mid bosh deployment
+      # we can probably clean this up in the future
+      web_instances || original_web_process_instance_count
+    end
+
     def current_canary_instance_target
       canary_step[:canary]
     end
@@ -133,11 +141,17 @@ def canary_step_plan
 
       return [{ canary: 1, original: original_web_process_instance_count }] if canary_steps.nil?
 
+      instances = if web_instances && web_instances < original_web_process_instance_count
+                    web_instances
+                  else
+                    original_web_process_instance_count
+                  end
+
       canary_steps.map do |step|
         weight = step['instance_weight']
-        target_canary = (original_web_process_instance_count * (weight.to_f / 100)).round.to_i
+        target_canary = (instances * (weight.to_f / 100)).round.to_i
         target_canary = 1 if target_canary.zero?
-        target_original = original_web_process_instance_count - target_canary + 1
+        target_original = instances - target_canary + 1
         target_original = 0 if weight == 100
         { canary: target_canary, original: target_original }
       end

app/presenters/v3/deployment_presenter.rb

@@ -57,7 +57,8 @@ def new_processes
 
     def options(deployment)
       options = {
-        max_in_flight: deployment.max_in_flight
+        max_in_flight: deployment.max_in_flight,
+        web_instances: deployment.desired_web_instances
       }
 
       if deployment.strategy == VCAP::CloudController::DeploymentModel::CANARY_STRATEGY && deployment.canary_steps

db/migrations/20250304215542_add_web_instances_to_deployments.rb

@@ -0,0 +1,12 @@
+Sequel.migration do
+  up do
+    alter_table(:deployments) do
+      add_column :web_instances, :integer, null: true
+    end
+  end
+  down do
+    alter_table(:deployments) do
+      drop_column :web_instances
+    end
+  end
+end

docs/v3/source/includes/api_resources/_deployments.erb

@@ -19,6 +19,7 @@
   "strategy": "canary",
   "options" : {
     "max_in_flight": 3,
+    "web_instances": 5,
     "canary": {
       "steps": [
         {

docs/v3/source/includes/resources/deployments/_create.md.erb

@@ -78,6 +78,7 @@ Name | Type | Description | Default
 **revision**<sup>[1]</sup> | _object_ | The [revision](#revisions) whose droplet to deploy for the app; this will update the app's [current droplet](#get-current-droplet-association-for-an-app) to this droplet |
 **strategy** | _string_ | The strategy to use for the deployment | `rolling`
 **options.max_in_flight** | _integer_ | The maximum number of new instances to deploy simultaneously | 1
+**options.web_instances** | _integer_ | The number of web instances the deployment will scale to | The current web process's instance count
 **options.canary.steps** | _array of [canary step objects](#canary-steps-object)_ | An array of canary steps to use for the deployment
 **metadata.labels** | [_label object_](#labels) | Labels applied to the deployment
 **metadata.annotations**  | [_annotation object_](#annotations) | Annotations applied to the deployment

docs/v3/source/includes/resources/deployments/_object.md.erb

@@ -20,6 +20,7 @@ Name | Type | Description
 **status.canary.steps.total** | _integer_ |  The total number of canary steps. Only available for deployments with strategy 'canary'. (experimental)
 **strategy** | _string_ | Strategy used for the deployment; supported strategies are `rolling` and `canary` (experimental)
 **options.max_in_flight** | _integer_ | The maximum number of new instances to deploy simultaneously
+**options.web_instances** | _integer_ | The number of web instances the deployment will scale to
 **options.canary.steps** | _array of [canary step objects](#canary-steps-object)_ | Canary steps to use for the deployment. Only available for deployments with strategy 'canary'. (experimental)
 **droplet.guid** | _string_ | The droplet guid that the deployment is transitioning the app to
 **previous_droplet.guid** | _string_ | The app's [current droplet guid](#get-current-droplet-association-for-an-app) before the deployment was created

lib/cloud_controller/deployment_updater/updater.rb

@@ -14,7 +14,7 @@ def initialize(deployment, logger)
 
       def scale
         with_error_logging('error-scaling-deployment') do
-          finished = Actions::Scale.new(deployment, logger, deployment.original_web_process_instance_count).call
+          finished = Actions::Scale.new(deployment, logger, deployment.desired_web_instances).call
           Actions::Finalize.new(deployment).call if finished
           logger.info("ran-deployment-update-for-#{deployment.guid}")
         end