Add logical backup (#442)

* Add k8s cron job to spawn logical backups

* Minor doc updates

pkg/util/k8sutil/k8sutil.go

@@ -6,8 +6,11 @@ import (
 
 	b64 "encoding/base64"
 
+	batchv1beta1 "k8s.io/api/batch/v1beta1"
+	clientbatchv1beta1 "k8s.io/client-go/kubernetes/typed/batch/v1beta1"
+
 	"github.com/zalando/postgres-operator/pkg/util/constants"
-	"k8s.io/api/core/v1"
+	v1 "k8s.io/api/core/v1"
 	policybeta1 "k8s.io/api/policy/v1beta1"
 	apiextclient "k8s.io/apiextensions-apiserver/pkg/client/clientset/clientset"
 	apiextbeta1 "k8s.io/apiextensions-apiserver/pkg/client/clientset/clientset/typed/apiextensions/v1beta1"
@@ -40,6 +43,7 @@ type KubernetesClient struct {
 	rbacv1beta1.RoleBindingsGetter
 	policyv1beta1.PodDisruptionBudgetsGetter
 	apiextbeta1.CustomResourceDefinitionsGetter
+	clientbatchv1beta1.CronJobsGetter
 
 	RESTClient      rest.Interface
 	AcidV1ClientSet *acidv1client.Clientset
@@ -101,6 +105,7 @@ func NewFromConfig(cfg *rest.Config) (KubernetesClient, error) {
 	kubeClient.PodDisruptionBudgetsGetter = client.PolicyV1beta1()
 	kubeClient.RESTClient = client.CoreV1().RESTClient()
 	kubeClient.RoleBindingsGetter = client.RbacV1beta1()
+	kubeClient.CronJobsGetter = client.BatchV1beta1()
 
 	apiextClient, err := apiextclient.NewForConfig(cfg)
 	if err != nil {
@@ -159,6 +164,28 @@ func SamePDB(cur, new *policybeta1.PodDisruptionBudget) (match bool, reason stri
 	return
 }
 
+func getJobImage(cronJob *batchv1beta1.CronJob) string {
+	return cronJob.Spec.JobTemplate.Spec.Template.Spec.Containers[0].Image
+}
+
+// SameLogicalBackupJob compares Specs of logical backup cron jobs
+func SameLogicalBackupJob(cur, new *batchv1beta1.CronJob) (match bool, reason string) {
+
+	if cur.Spec.Schedule != new.Spec.Schedule {
+		return false, fmt.Sprintf("new job's schedule %q doesn't match the current one %q",
+			new.Spec.Schedule, cur.Spec.Schedule)
+	}
+
+	newImage := getJobImage(new)
+	curImage := getJobImage(cur)
+	if newImage != curImage {
+		return false, fmt.Sprintf("new job's image %q doesn't match the current one %q",
+			newImage, curImage)
+	}
+
+	return true, ""
+}
+
 func (c *mockSecret) Get(name string, options metav1.GetOptions) (*v1.Secret, error) {
 	if name != "infrastructureroles-test" {
 		return nil, fmt.Errorf("NotFound")