feat: only redeploy formations that have had their values changed

Rather than redeploy every formation, only deploy formations that have had their values changed from the defaults.

This still doesn't handle the case where we touch existing processes when scaling _up_, but should decrease the number of services touched otherwise during scaling.

Also note that there are no tests for this new behavior yet (tests incoming).

Refs #7396

plugins/ps/functions.go

@@ -247,33 +247,77 @@ func scaleReport(appName string) error {
 	return nil
 }
 
-func scaleSet(appName string, skipDeploy bool, clearExisting bool, processTuples []string) error {
-	formations, err := parseProcessTuples(processTuples)
+// scaleSetInput is the input for the scaleSet function
+type scaleSetInput struct {
+	// appName is the name of the app to scale
+	appName string
+
+	// skipDeploy is a flag to skip the deploy phase
+	skipDeploy bool
+
+	// clearExisting is a flag to clear the existing scale
+	clearExisting bool
+
+	// processTuples is a list of process tuples to scale
+	processTuples []string
+
+	// deployOnlyChanged is a flag to deploy only the changed formations
+	deployOnlyChanged bool
+}
+
+func scaleSet(input scaleSetInput) error {
+	existingFormations, err := getFormations(input.appName)
 	if err != nil {
 		return err
 	}
 
-	if err := updateScale(appName, clearExisting, formations); err != nil {
-		return err
-	}
-
-	if skipDeploy {
-		return nil
-	}
-
-	if !common.IsDeployed(appName) {
-		return nil
-	}
-
-	imageTag, err := common.GetRunningImageTag(appName, "")
+	formations, err := parseProcessTuples(input.processTuples)
 	if err != nil {
 		return err
 	}
 
-	for _, formation := range formations {
+	if err := updateScale(input.appName, input.clearExisting, formations); err != nil {
+		return err
+	}
+
+	if input.skipDeploy {
+		return nil
+	}
+
+	if !common.IsDeployed(input.appName) {
+		return nil
+	}
+
+	imageTag, err := common.GetRunningImageTag(input.appName, "")
+	if err != nil {
+		return err
+	}
+
+	changedFormations := FormationSlice{}
+	if input.deployOnlyChanged {
+		for _, formation := range formations {
+			isChanged := true
+			for _, existingFormation := range existingFormations {
+				if existingFormation.ProcessType == formation.ProcessType {
+					if existingFormation.Quantity == formation.Quantity {
+						isChanged = false
+						break
+					}
+				}
+			}
+
+			if isChanged {
+				changedFormations = append(changedFormations, formation)
+			}
+		}
+	} else {
+		changedFormations = formations
+	}
+
+	for _, formation := range changedFormations {
 		_, err := common.CallPlugnTrigger(common.PlugnTriggerInput{
 			Trigger:     "deploy",
-			Args:        []string{appName, imageTag, formation.ProcessType},
+			Args:        []string{input.appName, imageTag, formation.ProcessType},
 			StreamStdio: true,
 		})
 		if err != nil {

plugins/ps/subcommands.go

@@ -160,7 +160,13 @@ func CommandScale(appName string, skipDeploy bool, processTuples []string) error
 	}
 
 	common.LogInfo1(fmt.Sprintf("Scaling %s processes: %s", appName, strings.Join(processTuples, " ")))
-	return scaleSet(appName, skipDeploy, false, processTuples)
+	return scaleSet(scaleSetInput{
+		appName:           appName,
+		skipDeploy:        skipDeploy,
+		clearExisting:     false,
+		processTuples:     processTuples,
+		deployOnlyChanged: true,
+	})
 }
 
 // CommandSet sets or clears a ps property for an app

plugins/ps/triggers.go

@@ -339,7 +339,13 @@ func TriggerPsCurrentScale(appName string) error {
 
 // TriggerPsSetScale configures the scale parameters for a given app
 func TriggerPsSetScale(appName string, skipDeploy bool, clearExisting bool, processTuples []string) error {
-	return scaleSet(appName, skipDeploy, clearExisting, processTuples)
+	return scaleSet(scaleSetInput{
+		appName:           appName,
+		skipDeploy:        skipDeploy,
+		clearExisting:     clearExisting,
+		processTuples:     processTuples,
+		deployOnlyChanged: false,
+	})
 }
 
 func TriggerPsGetProperty(appName string, property string) error {