Update watchPods() behavior for Patroni role change

Add an additional check to the existing watchPods function to
queue an event when an instance Pod is first given the 'master'
role.

Issue: PGO-190

Author: tjmoore4

internal/controller/postgrescluster/watches.go

@@ -57,6 +57,18 @@ func (*Reconciler) watchPods() handler.Funcs {
 				}})
 				return
 			}
+
+			// Queue an event to start applying changes if the PostgreSQL instance
+			// now has the "master" role.
+			if len(cluster) != 0 &&
+				!patroni.PodIsPrimary(e.ObjectOld) &&
+				patroni.PodIsPrimary(e.ObjectNew) {
+				q.Add(reconcile.Request{NamespacedName: client.ObjectKey{
+					Namespace: e.ObjectNew.GetNamespace(),
+					Name:      cluster,
+				}})
+				return
+			}
 		},
 	}
 }

internal/patroni/reconcile.go

@@ -181,6 +181,24 @@ func instanceProbes(cluster *v1beta1.PostgresCluster, container *corev1.Containe
 	}
 }
 
+// PodIsPrimary returns whether or not pod is currently acting as the leader with
+// the "master" role. This role will be called "primary" in the future, see:
+// - https://github.com/zalando/patroni/blob/master/docs/releases.rst?plain=1#L213
+func PodIsPrimary(pod metav1.Object) bool {
+	if pod == nil {
+		return false
+	}
+
+	// TODO(cbandy): This works only when using Kubernetes for DCS.
+
+	// - https://github.com/zalando/patroni/blob/v3.1.1/patroni/ha.py#L296
+	// - https://github.com/zalando/patroni/blob/v3.1.1/patroni/ha.py#L583
+	// - https://github.com/zalando/patroni/blob/v3.1.1/patroni/ha.py#L782
+	// - https://github.com/zalando/patroni/blob/v3.1.1/patroni/ha.py#L1574
+	status := pod.GetAnnotations()["status"]
+	return strings.Contains(status, `"role":"master"`)
+}
+
 // PodIsStandbyLeader returns whether or not pod is currently acting as a "standby_leader".
 func PodIsStandbyLeader(pod metav1.Object) bool {
 	if pod == nil {

internal/patroni/reconcile_test.go

@@ -231,6 +231,31 @@ volumes:
 	`))
 }
 
+func TestPodIsPrimary(t *testing.T) {
+	// No object
+	assert.Assert(t, !PodIsPrimary(nil))
+
+	// No annotations
+	pod := &corev1.Pod{}
+	assert.Assert(t, !PodIsPrimary(pod))
+
+	// No role
+	pod.Annotations = map[string]string{"status": `{}`}
+	assert.Assert(t, !PodIsPrimary(pod))
+
+	// Replica
+	pod.Annotations["status"] = `{"role":"replica"}`
+	assert.Assert(t, !PodIsPrimary(pod))
+
+	// Standby leader
+	pod.Annotations["status"] = `{"role":"standby_leader"}`
+	assert.Assert(t, !PodIsPrimary(pod))
+
+	// Primary
+	pod.Annotations["status"] = `{"role":"master"}`
+	assert.Assert(t, PodIsPrimary(pod))
+}
+
 func TestPodIsStandbyLeader(t *testing.T) {
 	// No object
 	assert.Assert(t, !PodIsStandbyLeader(nil))