adding etcd overview

Author: lahinson

architecture/control-plane.adoc

@@ -52,6 +52,13 @@ include::modules/understanding-machine-config-operator.adoc[leveloffset=+1]
 
 * For information about preventing the control plane machines from rebooting after the Machine Config Operator makes changes to the machine configuration, see xref:../support/troubleshooting/troubleshooting-operator-issues.adoc#troubleshooting-disabling-autoreboot-mco_troubleshooting-operator-issues[Disabling Machine Config Operator from automatically rebooting].
 
+include::modules/etcd-overview.adoc[leveloffset=+1]
+
+[role="_additional-resources"]
+.Additional resources
+* xref:../scalability_and_performance/recommended-host-practices.adoc#recommended-etcd-practices_recommended-host-practices[Recommended etcd practices]
+* xref:../backup_and_restore/control_plane_backup_and_restore/backing-up-etcd.adoc#backing-up-etcd[Backing up etcd]
+
 include::modules/hosted-control-planes-overview.adoc[leveloffset=+1]
 
 [role="_additional-resources"]

modules/etcd-overview.adoc

@@ -0,0 +1,32 @@
+// Module included in the following assemblies:
+//
+// * architecture/control-plane.adoc
+
+
+:_content-type: CONCEPT
+[id="etcd-overview_{context}"]
+= Overview of etcd
+
+etcd is a consistent, distributed key-value store that holds small amounts of data that can fit entirely in memory. Although etcd is a core component of many projects, it is the primary data store for Kubernetes, which is the standard system for container orchestration.
+
+[id="etcd-benefits_{context}"]
+== Benefits of using etcd
+
+By using etcd, you can benefit in several ways:
+
+* Maintain consistent uptime for your cloud-native applications, and keep them working even if individual servers fail
+* Store and replicate all cluster states for Kubernetes
+* Distribute configuration data to provide redundancy and resiliency for the configuration of nodes
+
+[id="etcd-architecture_{context}"]
+== How etcd works
+
+To ensure a reliable approach to cluster configuration and management, etcd uses the etcd Operator. The Operator simplifies the use of etcd on a Kubernetes container platform like {product-title}. With the etcd Operator, you can create or delete etcd members, resize clusters, perform backups, and upgrade etcd.
+
+The etcd Operator observes, analyzes, and acts:
+
+. It observes the cluster state by using the Kubernetes API.
+. It analyzes differences between the current state and the state that you want.
+. It fixes the differences through the etcd cluster management APIs, the Kubernetes API, or both.
+
+etcd holds the cluster state, which is constantly updated. This state is continuously persisted, which leads to a high number of small changes at high frequency. As a result, it is critical to back the etcd cluster member with fast, low-latency I/O. For more information about best practices for etcd, see "Recommended etcd practices".