Check rolling updates using controller revisions.

Compare pods controller revisions with the one for the statefulset
to determine whether the pod is running the latest revision and,
therefore, no rolling update is necessary. This is performed only
during the operator start, afterwards the rolling update status
that is stored locally in the cluster structure is used for all
rolling update decisions.

pkg/cluster/util.go

@@ -39,6 +39,10 @@ func NewSecretOauthTokenGetter(kubeClient *k8sutil.KubernetesClient,
 	return &SecretOauthTokenGetter{kubeClient, OAuthTokenSecretName}
 }
 
+const (
+	podControllerRevisionHashLabel = "controller-revision-hash"
+)
+
 func (g *SecretOauthTokenGetter) getOAuthToken() (string, error) {
 	//TODO: we can move this function to the Controller in case it will be needed there. As for now we use it only in the Cluster
 	// Temporary getting postgresql-operator secret from the NamespaceDefault
@@ -430,3 +434,56 @@ func (c *Cluster) GetSpec() (*spec.Postgresql, error) {
 func (c *Cluster) patroniUsesKubernetes() bool {
 	return c.OpConfig.EtcdHost == ""
 }
+
+func (c *Cluster) setPendingRollingUpgrade(val bool) {
+	if c.pendingRollingUpdate == nil {
+		c.pendingRollingUpdate = new(bool)
+	}
+	*c.pendingRollingUpdate = val
+	c.logger.Debugf("pending rolling upgrade was set to %b", val)
+}
+
+// resolvePendingRollingUpdate figures out if rolling upgrade is necessary
+// based on the states of the cluster statefulset and pods
+func (c *Cluster) resolvePendingRollingUpdate(sset *v1beta1.StatefulSet) error {
+	// XXX: it looks like we will always trigger a rolling update if the
+	// pods are on a different revision from a statefulset, even if the
+	// statefulset change that caused it didn't require a rolling update
+	// originally.
+	if c.pendingRollingUpdate != nil {
+		return nil
+	}
+	c.logger.Debugf("evaluating rolling upgrade requirement")
+	effectiveRevision := sset.Status.UpdateRevision
+	if effectiveRevision == "" {
+		if sset.Status.CurrentRevision == "" {
+			c.logger.Debugf("statefulset doesn't have a current revision, no rolling upgrade")
+			// the statefulset does not have a currentRevision, it must be new; hence, no rollingUpdate
+			c.setPendingRollingUpgrade(false)
+			return nil
+		}
+		effectiveRevision = sset.Status.CurrentRevision
+	}
+
+	// fetch all pods related to this cluster
+	pods, err := c.listPods()
+	if err != nil {
+		return err
+	}
+	// check their revisions
+	for _, pod := range pods {
+		podRevision, present := pod.Labels[podControllerRevisionHashLabel]
+		// empty or missing revision indicates a new pod - doesn't need a rolling upgrade
+		if !present || podRevision == "" {
+			continue
+		}
+		c.logger.Debugf("observing pod revision %q vs statefulset revision %q", podRevision, effectiveRevision)
+		if podRevision != effectiveRevision {
+			// pod is on a different revision - trigger the rolling upgrade
+			c.setPendingRollingUpgrade(true)
+			return nil
+		}
+	}
+	c.setPendingRollingUpgrade(false)
+	return nil
+}