OSDOCS#12348: Migrating etcd overview docs to new etcd book

etcd/etcd-overview.adoc

@@ -4,4 +4,27 @@ include::_attributes/common-attributes.adoc[]
 = Overview of etcd
 :context: etcd-overview
 
-// This assembly will contain modules to provide an overview of etcd.
+toc::[]
+
+etcd (pronounced et-see-dee) is a consistent, distributed key-value store that stores small amounts of data across a cluster of machines 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. 
+
+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 offer redundancy and resiliency for the configuration of nodes
+
+The etcd Operator creates and maintains highly-available etcd clusters on Kubernetes, allowing you to easily deploy and manage etcd clusters for your applications.
+
+[IMPORTANT]
+====
+The default etcd configuration optimizes container orchestration. Use it as prescribed for the best experience.
+====
+
+// How etcd works
+include::modules/how-etcd-works.adoc[leveloffset=+1]
+
+// [role="_additional-resources"]
+// .Additional resources
+// * xref:../etcd-practices.adoc#etcd-practices[Recommended etcd practices]
+// * xref:../etcd-backup.adoc#etcd-backup[Backing up and restoring etcd data]

modules/how-etcd-works.adoc

@@ -0,0 +1,21 @@
+// Module included in the following assemblies:
+// * etcd/etcd-overview.adoc
+
+:_mod-docs-content-type: CONCEPT
+[id="how-etcd-works_{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 such as {product-title}. With the etcd Operator, you can complete the following tasks: 
+
+* Create or delete etcd members 
+* Resize clusters 
+* Perform backups
+* Upgrade etcd 
+
+Additionally, use the etcd Operator to deploy and manage etcd clusters for your applications. The etcd Operator:
+
+* Observes the cluster state by using the Kubernetes API.
+* Analyzes differences between the current state and the desired state.
+* Corrects 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 up the etcd cluster member with fast, low-latency I/O. For more information about best practices for etcd, see _Recommended etcd practices_.