GCP: Add additional checks for compact cluster installs

Add checks around number of compute replicas requested, the number
of worker manifests and whether masters are schedulable. These are
useful especially for compact cluster installs.

Author: sadasu

pkg/asset/cluster/tfvars/tfvars.go

@@ -15,6 +15,7 @@ import (
 	coreosarch "github.com/coreos/stream-metadata-go/arch"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
+	"k8s.io/utils/ptr"
 	"sigs.k8s.io/yaml"
 
 	configv1 "github.com/openshift/api/config/v1"
@@ -214,6 +215,11 @@ func (t *TerraformVariables) Generate(parents asset.Parents) error {
 		return errors.Errorf("master slice cannot be empty")
 	}
 
+	numWorkers := int64(0)
+	for _, worker := range installConfig.Config.Compute {
+		numWorkers += ptr.Deref(worker.Replicas, 0)
+	}
+
 	switch platform {
 	case aws.Name:
 		var vpc string
@@ -267,13 +273,7 @@ func (t *TerraformVariables) Generate(parents asset.Parents) error {
 		if err != nil {
 			return err
 		}
-		// Based on the number of workers, we could have the following outcomes:
-		// 1. workers > 0, masters not schedulable, valid cluster
-		// 2. workers = 0, masters schedulable, valid compact cluster but currently unsupported
-		// 3. workers = 0, masters not schedulable, invalid cluster
-		if len(workers) == 0 {
-			return errors.Errorf("compact clusters with 0 workers are not supported at this time")
-		}
+
 		workerConfigs := make([]*machinev1beta1.AWSMachineProviderConfig, len(workers))
 		for i, m := range workers {
 			workerConfigs[i] = m.Spec.Template.Spec.ProviderSpec.Value.Object.(*machinev1beta1.AWSMachineProviderConfig) //nolint:errcheck // legacy, pre-linter
@@ -372,13 +372,6 @@ func (t *TerraformVariables) Generate(parents asset.Parents) error {
 		if err != nil {
 			return err
 		}
-		// Based on the number of workers, we could have the following outcomes:
-		// 1. workers > 0, masters not schedulable, valid cluster
-		// 2. workers = 0, masters schedulable, valid compact cluster but currently unsupported
-		// 3. workers = 0, masters not schedulable, invalid cluster
-		if len(workers) == 0 {
-			return errors.Errorf("compact clusters with 0 workers are not supported at this time")
-		}
 		workerConfigs := make([]*machinev1beta1.AzureMachineProviderSpec, len(workers))
 		for i, w := range workers {
 			workerConfigs[i] = w.Spec.Template.Spec.ProviderSpec.Value.Object.(*machinev1beta1.AzureMachineProviderSpec) //nolint:errcheck // legacy, pre-linter
@@ -495,12 +488,16 @@ func (t *TerraformVariables) Generate(parents asset.Parents) error {
 			return err
 		}
 		// Based on the number of workers, we could have the following outcomes:
-		// 1. workers > 0, masters not schedulable, valid cluster
-		// 2. workers = 0, masters schedulable, valid compact cluster but currently unsupported
-		// 3. workers = 0, masters not schedulable, invalid cluster
-		if len(workers) == 0 {
-			return errors.Errorf("compact clusters with 0 workers are not supported at this time")
+		// 1. compute replicas > 0, worker machinesets > 0, masters not schedulable, valid cluster
+		// 2. compute replicas > 0, worker machinesets = 0, invalid cluster
+		// 3. compute replicas = 0, masters schedulable, valid cluster
+		if numWorkers != 0 && len(workers) == 0 {
+			return fmt.Errorf("invalid configuration. No worker assets available for requested number of compute replicas (%d)", numWorkers)
 		}
+		if numWorkers == 0 && !mastersSchedulable {
+			return fmt.Errorf("invalid configuration. No workers requested but masters are not schedulable")
+		}
+
 		workerConfigs := make([]*machinev1beta1.GCPMachineProviderSpec, len(workers))
 		for i, w := range workers {
 			workerConfigs[i] = w.Spec.Template.Spec.ProviderSpec.Value.Object.(*machinev1beta1.GCPMachineProviderSpec) //nolint:errcheck // legacy, pre-linter