[placement] Allow zone to be overridden

This allows us to direct placement writes
to an etcd cluster other than the hardcoded "embedded"
zone.

pkg/apis/m3dboperator/v1alpha1/cluster.go

@@ -323,6 +323,11 @@ type ClusterSpec struct {
 	// OnDeleteUpdateStrategy sets StatefulSets created by the operator to
 	// have OnDelete as the update strategy instead of RollingUpdate.
 	OnDeleteUpdateStrategy bool `json:"onDeleteUpdateStrategy,omitempty"`
+
+	// Zone defines the zone that placement instances will be written to if set.
+	// If not set, the default zone of "embedded" will be used.
+	// +optional
+	Zone string `json:"zone,omitempty"`
 }
 
 // ExternalCoordinatorConfig defines parameters for using an external

pkg/k8sops/m3db/placement.go

@@ -88,10 +88,15 @@ func PlacementInstanceFromPod(cluster *myspec.M3DBCluster, pod *corev1.Pod, idPr
 		return nil, pkgerrors.WithMessage(err, "cannot execute node endpoint template")
 	}
 
+	zone := cluster.Spec.Zone
+	if zone == "" {
+		zone = _zoneEmbedded
+	}
+
 	instance := &placementpb.Instance{
 		Id:             idStr,
 		IsolationGroup: isoGroup,
-		Zone:           _zoneEmbedded,
+		Zone:           zone,
 		Weight:         100,
 		Hostname:       pod.Name + "." + epCtx.M3DBService,
 		Endpoint:       str.String(),

pkg/k8sops/m3db/placement_test.go

@@ -86,6 +86,22 @@ func TestPlacementInstanceFromPod(t *testing.T) {
 			Port:           9000,
 		}
 
+		inst, err := PlacementInstanceFromPod(cluster, pod, idProvider)
+		assert.NoError(t, err)
+		assert.Equal(t, expInst, inst)
+	})
+	t.Run("zone override", func(t *testing.T) {
+		cluster.Spec.Zone = "embedded-override"
+		expInst := &placementpb.Instance{
+			Id:             `{"name":"pod-a"}`,
+			IsolationGroup: "zone-a",
+			Zone:           "embedded-override",
+			Weight:         100,
+			Hostname:       "pod-a.m3dbnode-cluster-a",
+			Endpoint:       "pod-a.m3dbnode-cluster-a.my_ns:9000",
+			Port:           9000,
+		}
+
 		inst, err := PlacementInstanceFromPod(cluster, pod, idProvider)
 		assert.NoError(t, err)
 		assert.Equal(t, expInst, inst)