Set the ServiceName for new StatefulSets (#305)

* make sure the ServiceName is set

* update changelog

CHANGELOG.md

@@ -9,6 +9,10 @@ Changelog for Cass Operator, new PRs should update the `main / unreleased` secti
 * [BUGFIX]
 ```
 
+## unreleased
+
+* [BUGFIX] [#304](https://github.com/k8ssandra/cass-operator/issues/304) Hostname lookups on Cassandra pods fail
+
 ## v1.10.1
 
 * [BUGFIX] [#278](https://github.com/k8ssandra/cass-operator/issues/278) ImageRegistry json key was incorrect in the definition type. Fixed from "imageRegistryOverride" to "imageRegistry"

pkg/reconciliation/construct_statefulset.go

@@ -179,7 +179,7 @@ func newStatefulSetForCassandraDatacenter(
 	}
 	result.Annotations = map[string]string{}
 
-	if sts != nil && sts.Spec.ServiceName != result.Spec.ServiceName {
+	if sts != nil && sts.Spec.ServiceName != "" && sts.Spec.ServiceName != result.Spec.ServiceName {
 		result.Spec.ServiceName = sts.Spec.ServiceName
 	}
 

pkg/reconciliation/construct_statefulset_test.go

@@ -6,6 +6,8 @@ package reconciliation
 import (
 	"fmt"
 	"github.com/k8ssandra/cass-operator/pkg/oplabels"
+	"github.com/stretchr/testify/require"
+	appsv1 "k8s.io/api/apps/v1"
 	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"reflect"
 	"testing"
@@ -152,6 +154,25 @@ func Test_newStatefulSetForCassandraDatacenter_rackNodeAffinitylabels(t *testing
 	assert.Equal(t, expected, nodeAffinityLabels)
 }
 
+func Test_newStatefulSetForCassandraDatacenter_ServiceName(t *testing.T) {
+	dc := &api.CassandraDatacenter{
+		Spec: api.CassandraDatacenterSpec{
+			ClusterName:   "test",
+			ServerType:    "cassandra",
+			ServerVersion: "4.0.3",
+			Size:          1,
+			StorageConfig: api.StorageConfig{
+				CassandraDataVolumeClaimSpec: &corev1.PersistentVolumeClaimSpec{},
+			},
+		},
+	}
+
+	sts, err := newStatefulSetForCassandraDatacenter(&appsv1.StatefulSet{}, "default", dc, 1, false)
+
+	require.NoError(t, err)
+	assert.Equal(t, dc.GetAllPodsServiceName(), sts.Spec.ServiceName)
+}
+
 func Test_newStatefulSetForCassandraDatacenterWithAdditionalVolumes(t *testing.T) {
 	type args struct {
 		rackName     string