Don't create an impossible disruption budget for smaller clusters.

pkg/cluster/k8sres.go

@@ -1052,6 +1052,11 @@ func (c *Cluster) generateCloneEnvironment(description *acidv1.CloneDescription)
 func (c *Cluster) generatePodDisruptionBudget() *policybeta1.PodDisruptionBudget {
 	minAvailable := intstr.FromInt(1)
 
+	// Avoid creating an unsatisfyable budget.
+	if c.Spec.NumberOfInstances <= 1 {
+		minAvailable = intstr.FromInt(0)
+	}
+
 	return &policybeta1.PodDisruptionBudget{
 		ObjectMeta: metav1.ObjectMeta{
 			Name:      c.podDisruptionBudgetName(),

pkg/cluster/k8sres_test.go

@@ -4,7 +4,12 @@ import (
 	acidv1 "github.com/zalando-incubator/postgres-operator/pkg/apis/acid.zalan.do/v1"
 	"github.com/zalando-incubator/postgres-operator/pkg/util/config"
 	"github.com/zalando-incubator/postgres-operator/pkg/util/k8sutil"
+	"reflect"
 	"testing"
+
+	policyv1beta1 "k8s.io/api/policy/v1beta1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/util/intstr"
 )
 
 func True() *bool {
@@ -17,6 +22,11 @@ func False() *bool {
 	return &b
 }
 
+func toIntStr(val int) *intstr.IntOrString {
+	b := intstr.FromInt(val)
+	return &b
+}
+
 func TestCreateLoadBalancerLogic(t *testing.T) {
 	var cluster = New(
 		Config{
@@ -75,3 +85,87 @@ func TestCreateLoadBalancerLogic(t *testing.T) {
 		}
 	}
 }
+
+func TestGeneratePodDisruptionBudget(t *testing.T) {
+	tests := []struct {
+		c   *Cluster
+		out policyv1beta1.PodDisruptionBudget
+	}{
+		// With multiple instances.
+		{
+			New(
+				Config{OpConfig: config.Config{Resources: config.Resources{ClusterNameLabel: "cluster-name", PodRoleLabel: "spilo-role"}, PDBNameFormat: "postgres-{cluster}-pdb"}},
+				k8sutil.KubernetesClient{},
+				acidv1.Postgresql{
+					ObjectMeta: metav1.ObjectMeta{Name: "myapp-database", Namespace: "myapp"},
+					Spec:       acidv1.PostgresSpec{TeamID: "myapp", NumberOfInstances: 3}},
+				logger),
+			policyv1beta1.PodDisruptionBudget{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "postgres-myapp-database-pdb",
+					Namespace: "myapp",
+					Labels:    map[string]string{"team": "myapp", "cluster-name": "myapp-database"},
+				},
+				Spec: policyv1beta1.PodDisruptionBudgetSpec{
+					MinAvailable: toIntStr(1),
+					Selector: &metav1.LabelSelector{
+						MatchLabels: map[string]string{"spilo-role": "master", "cluster-name": "myapp-database"},
+					},
+				},
+			},
+		},
+		// With a single instance.
+		{
+			New(
+				Config{OpConfig: config.Config{Resources: config.Resources{ClusterNameLabel: "cluster-name", PodRoleLabel: "spilo-role"}, PDBNameFormat: "postgres-{cluster}-pdb"}},
+				k8sutil.KubernetesClient{},
+				acidv1.Postgresql{
+					ObjectMeta: metav1.ObjectMeta{Name: "myapp-database", Namespace: "myapp"},
+					Spec:       acidv1.PostgresSpec{TeamID: "myapp", NumberOfInstances: 1}},
+				logger),
+			policyv1beta1.PodDisruptionBudget{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "postgres-myapp-database-pdb",
+					Namespace: "myapp",
+					Labels:    map[string]string{"team": "myapp", "cluster-name": "myapp-database"},
+				},
+				Spec: policyv1beta1.PodDisruptionBudgetSpec{
+					MinAvailable: toIntStr(0),
+					Selector: &metav1.LabelSelector{
+						MatchLabels: map[string]string{"spilo-role": "master", "cluster-name": "myapp-database"},
+					},
+				},
+			},
+		},
+		// With non-default PDBNameFormat.
+		{
+			New(
+				Config{OpConfig: config.Config{Resources: config.Resources{ClusterNameLabel: "cluster-name", PodRoleLabel: "spilo-role"}, PDBNameFormat: "postgres-{cluster}-databass-budget"}},
+				k8sutil.KubernetesClient{},
+				acidv1.Postgresql{
+					ObjectMeta: metav1.ObjectMeta{Name: "myapp-database", Namespace: "myapp"},
+					Spec:       acidv1.PostgresSpec{TeamID: "myapp", NumberOfInstances: 3}},
+				logger),
+			policyv1beta1.PodDisruptionBudget{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "postgres-myapp-database-databass-budget",
+					Namespace: "myapp",
+					Labels:    map[string]string{"team": "myapp", "cluster-name": "myapp-database"},
+				},
+				Spec: policyv1beta1.PodDisruptionBudgetSpec{
+					MinAvailable: toIntStr(1),
+					Selector: &metav1.LabelSelector{
+						MatchLabels: map[string]string{"spilo-role": "master", "cluster-name": "myapp-database"},
+					},
+				},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		result := tt.c.generatePodDisruptionBudget()
+		if !reflect.DeepEqual(*result, tt.out) {
+			t.Errorf("Expected PodDisruptionBudget: %#v, got %#v", tt.out, *result)
+		}
+	}
+}