Re-create pods only if all replicas are running (zalando#903)

* adds a Get call to Patroni interface to fetch state of a Patroni member
* postpones re-creating pods if at least one replica is currently being created  

Co-authored-by: Sergey Dudoladov <[email protected]>
Co-authored-by: Felix Kunde <[email protected]>

Author: 3 people

.gitignore

@@ -28,6 +28,7 @@ _testmain.go
 /vendor/
 /build/
 /docker/build/
+/github.com/
 .idea
 
 scm-source.json

e2e/tests/test_e2e.py

@@ -344,7 +344,6 @@ def test_node_readiness_label(self):
         '''
         k8s = self.k8s
         cluster_label = 'application=spilo,cluster-name=acid-minimal-cluster'
-        labels = 'spilo-role=master,' + cluster_label
         readiness_label = 'lifecycle-status'
         readiness_value = 'ready'
 
@@ -709,14 +708,16 @@ def wait_for_logical_backup_job_deletion(self):
     def wait_for_logical_backup_job_creation(self):
         self.wait_for_logical_backup_job(expected_num_of_jobs=1)
 
-    def update_config(self, config_map_patch):
-        self.api.core_v1.patch_namespaced_config_map("postgres-operator", "default", config_map_patch)
-
+    def delete_operator_pod(self):
         operator_pod = self.api.core_v1.list_namespaced_pod(
             'default', label_selector="name=postgres-operator").items[0].metadata.name
         self.api.core_v1.delete_namespaced_pod(operator_pod, "default")  # restart reloads the conf
         self.wait_for_operator_pod_start()
 
+    def update_config(self, config_map_patch):
+        self.api.core_v1.patch_namespaced_config_map("postgres-operator", "default", config_map_patch)
+        self.delete_operator_pod()
+
     def create_with_kubectl(self, path):
         return subprocess.run(
             ["kubectl", "create", "-f", path],

pkg/cluster/pod.go

@@ -294,6 +294,27 @@ func (c *Cluster) recreatePod(podName spec.NamespacedName) (*v1.Pod, error) {
 	return pod, nil
 }
 
+func (c *Cluster) isSafeToRecreatePods(pods *v1.PodList) bool {
+
+	/*
+	 Operator should not re-create pods if there is at least one replica being bootstrapped
+	 because Patroni might use other replicas to take basebackup from (see Patroni's "clonefrom" tag).
+
+	 XXX operator cannot forbid replica re-init, so we might still fail if re-init is started
+	 after this check succeeds but before a pod is re-created
+	*/
+
+	for _, pod := range pods.Items {
+		state, err := c.patroni.GetPatroniMemberState(&pod)
+		if err != nil || state == "creating replica" {
+			c.logger.Warningf("cannot re-create replica %s: it is currently being initialized", pod.Name)
+			return false
+		}
+
+	}
+	return true
+}
+
 func (c *Cluster) recreatePods() error {
 	c.setProcessName("starting to recreate pods")
 	ls := c.labelsSet(false)
@@ -309,6 +330,10 @@ func (c *Cluster) recreatePods() error {
 	}
 	c.logger.Infof("there are %d pods in the cluster to recreate", len(pods.Items))
 
+	if !c.isSafeToRecreatePods(pods) {
+		return fmt.Errorf("postpone pod recreation until next Sync: recreation is unsafe because pods are being initilalized")
+	}
+
 	var (
 		masterPod, newMasterPod, newPod *v1.Pod
 	)

pkg/util/patroni/patroni.go

@@ -3,6 +3,7 @@ package patroni
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"net"
@@ -11,7 +12,7 @@ import (
 	"time"
 
 	"github.com/sirupsen/logrus"
-	"k8s.io/api/core/v1"
+	v1 "k8s.io/api/core/v1"
 )
 
 const (
@@ -25,6 +26,7 @@ const (
 type Interface interface {
 	Switchover(master *v1.Pod, candidate string) error
 	SetPostgresParameters(server *v1.Pod, options map[string]string) error
+	GetPatroniMemberState(pod *v1.Pod) (string, error)
 }
 
 // Patroni API client
@@ -123,3 +125,36 @@ func (p *Patroni) SetPostgresParameters(server *v1.Pod, parameters map[string]st
 	}
 	return p.httpPostOrPatch(http.MethodPatch, apiURLString+configPath, buf)
 }
+
+//GetPatroniMemberState returns a state of member of a Patroni cluster
+func (p *Patroni) GetPatroniMemberState(server *v1.Pod) (string, error) {
+
+	apiURLString, err := apiURL(server)
+	if err != nil {
+		return "", err
+	}
+	response, err := p.httpClient.Get(apiURLString)
+	if err != nil {
+		return "", fmt.Errorf("could not perform Get request: %v", err)
+	}
+	defer response.Body.Close()
+
+	body, err := ioutil.ReadAll(response.Body)
+	if err != nil {
+		return "", fmt.Errorf("could not read response: %v", err)
+	}
+
+	data := make(map[string]interface{})
+	err = json.Unmarshal(body, &data)
+	if err != nil {
+		return "", err
+	}
+
+	state, ok := data["state"].(string)
+	if !ok {
+		return "", errors.New("Patroni Get call response contains wrong type for 'state' field")
+	}
+
+	return state, nil
+
+}