Re-create pods only if all replicas are running (#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 <sergey.dudoladov@zalando.de>
Co-authored-by: Felix Kunde <felix-kunde@gmx.de>

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
+
+}