JIRA2582: include overview for the backup and restore book

    pick a520911be JIRA2582: include overview for the backup and restore book

Author: chinmayi-chandrasekar

_topic_map.yml

@@ -2127,6 +2127,8 @@ Name: Backup and restore
 Dir: backup_and_restore
 Distros: openshift-origin,openshift-enterprise
 Topics:
+- Name: Overview of backup and restore operations
+  File: index
 - Name: Shutting down a cluster gracefully
   File: graceful-cluster-shutdown
 - Name: Restarting a cluster gracefully

backup_and_restore/index.adoc

@@ -0,0 +1,29 @@
+[id="backup-restore-overview"]
+= Backup and restore
+include::modules/common-attributes.adoc[]
+:context: backup-restore-overview
+
+toc::[]
+
+
+[id="backup-restore-operations-overview"]
+== Overview of backup and restore operations in {product-title}
+
+As a cluster administrator, you might need to stop an {product-title} cluster for a period and restart it later. Some reasons for restarting a cluster are that you need to perform maintenance on a cluster or want to reduce resource costs. In {product-title}, you can perform a xref:../backup_and_restore/graceful-cluster-shutdown.adoc#graceful-shutdown-cluster[graceful shutdown of a cluster] so that you can easily restart the cluster later.
+
+You must xref:../backup_and_restore/control_plane_backup_and_restore/backing-up-etcd.adoc#backup-etcd[back up etcd data] before shutting down a cluster; etcd is the key-value store for {product-title}, which persists the state of all resource objects. An etcd backup plays a crucial role in disaster recovery. In {product-title}, you can also xref:../backup_and_restore/control_plane_backup_and_restore/replacing-unhealthy-etcd-member.adoc#replacing-unhealthy-etcd-member[replace an unhealthy etcd member].
+
+When you want to get your cluster running again, xref:../backup_and_restore/graceful-cluster-restart.adoc#graceful-restart-cluster[restart the cluster gracefully].
+
+[NOTE]
+====
+A cluster's certificates expire one year after the installation date. You can shut down a cluster and expect it to restart gracefully while the certificates are still valid. Although the cluster automatically retrieves the expired control plane certificates, you must still xref:../backup_and_restore/control_plane_backup_and_restore/disaster_recovery/scenario-3-expired-certs.adoc#dr-recovering-expired-certs[approve the certificate signing requests (CSRs)].
+====
+
+You might run into several situations where {product-title}  does not work as expected, such as:
+
+* You have a cluster that is not functional after the restart because of unexpected conditions, such as node failure, or network connectivity issues.
+* You have deleted something critical in the cluster by mistake.
+* You have lost the majority of your control plane hosts, leading to etcd quorum loss.
+
+You can always recover from a disaster situation by xref:../backup_and_restore/control_plane_backup_and_restore/disaster_recovery/scenario-2-restoring-cluster-state.adoc#dr-restoring-cluster-state[restoring your cluster to its previous state] using the saved etcd snapshots.