Merge pull request #23737 from sftim/20200907_add_workload_concept_introduction

Add introduction to Workloads concept

Author: k8s-ci-robot

content/en/docs/concepts/workloads/_index.md

@@ -3,5 +3,55 @@ title: "Workloads"
 weight: 50
 description: >
   Understand Pods, the smallest deployable compute object in Kubernetes, and the higher-level abstractions that help you to run them.
+no_list: true
 ---
 
+{{< glossary_definition term_id="workload" length="short" >}}
+Whether your workload is a single component or several that work together, on Kubernetes you run
+it inside a set of [Pods](/docs/concepts/workloads/pods).
+In Kubernetes, a Pod represents a set of running {{< glossary_tooltip text="containers" term_id="container" >}}
+on your cluster.
+
+A Pod has a defined lifecycle. For example, once a Pod is running in your cluster then
+a critical failure on the {{< glossary_tooltip text="node" term_id="node" >}} where that
+Pod is running means that all the Pods on that node fail. Kubernetes treats that level
+of failure as final: you would need to create a new Pod even if the node later recovers.
+
+However, to make life considerably easier, you don't need to manage each Pod directly.
+Instead, you can use _workload resources_ that manage a set of Pods on your behalf.
+These resources configure {{< glossary_tooltip term_id="controller" text="controllers" >}}
+that make sure the right number of the right kind of Pod are running, to match the state
+you specified.
+
+Those workload resources include:
+
+* [Deployment](/docs/concepts/workloads/controllers/deployment/) and [ReplicaSet](/docs/concepts/workloads/controllers/replicaset/)
+  (replacing the legacy resource {{< glossary_tooltip text="ReplicationController" term_id="replication-controller" >}});
+* [StatefulSet](/docs/concepts/workloads/controllers/statefulset/);
+* [DaemonSet](/docs/concepts/workloads/controllers/daemonset/) for running Pods that provide
+  node-local facilities, such as a storage driver or network plugin;
+* [Job](/docs/concepts/workloads/controllers/job/) and
+  [CronJob](/docs/concepts/workloads/controllers/cronjob/)
+  for tasks that run to completion.
+
+There are also two supporting concepts that you might find relevant:
+* [Garbage collection](/docs/concepts/workloads/controllers/garbage-collection/) tidies up objects
+  from your cluster after their _owning resource_ has been removed.
+* The [_time-to-live after finished_ controller](/docs/concepts/workloads/controllers/ttlafterfinished/)
+  removes Jobs once a defined time has passed since they completed.
+
+## {{% heading "whatsnext" %}}
+
+As well as reading about each resource, you can learn about specific tasks that relate to them:
+
+* [Run a stateless application using a Deployment](/docs/tasks/run-application/run-stateless-application-deployment/)
+* Run a stateful application either as a [single instance](/docs/tasks/run-application/run-single-instance-stateful-application/)
+  or as a [replicated set](/docs/tasks/run-application/run-replicated-stateful-application/)
+* [Run Automated Tasks with a CronJob](/docs/tasks/job/automated-tasks-with-cron-jobs/)
+
+Once your application is running, you might want to make it available on the internet as
+a [Service](/docs/concepts/services-networking/service/) or, for web application only,
+using an [Ingress](/docs/concepts/services-networking/ingress).
+
+You can also visit [Configuration](/docs/concepts/configuration/) to learn about Kubernetes'
+mechanisms for separating code from configuration.

content/en/docs/concepts/workloads/controllers/_index.md

@@ -1,5 +1,5 @@
 ---
-title: "Controllers"
+title: "Workload Resources"
 weight: 20
 ---