Merge pull request #24602 from sftim/20201015_tweak_workloads_concept_overview

Tweak wording for Workloads overview

Author: k8s-ci-robot

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

@@ -8,50 +8,74 @@ 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.
+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.
+Kubernetes pods have a [defined lifecycle](/docs/concepts/workloads/pods/pod-lifecycle/).
+For example, once a pod is running in your cluster then a critical fault 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` to recover, even if the node later becomes healthy.
 
-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.
+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
+that make sure the right number of the right kind of pod are running, to match the state
 you specified.
 
-Those workload resources include:
+Kubernetes provides several built-in workload resources:
 
-* [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/cron-jobs/)
-  for tasks that run to completion.
+* [`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" >}}).
+  `Deployment` is a good fit for managing a stateless application workload on your cluster,
+  where any `Pod` in the `Deployment` is interchangeable and can be replaced if needed.
+* [`StatefulSet`](/docs/concepts/workloads/controllers/statefulset/) lets you
+  run one or more related Pods that do track state somehow. For example, if your workload
+  records data persistently, you can run a `StatefulSet` that matches each `Pod` with a
+  [`PersistentVolume`](/docs/concepts/storage/persistent-volumes/). Your code, running in the
+  `Pods` for that `StatefulSet`, can replicate data to other `Pods` in the same `StatefulSet`
+  to improve overall resilience.
+* [`DaemonSet`](/docs/concepts/workloads/controllers/daemonset/) defines `Pods` that provide
+  node-local facilities. These might be fundamental to the operation of your cluster, such
+  as a networking helper tool, or be part of an
+  {{< glossary_tooltip text="add-on" term_id="addons" >}}.  
+  Every time you add a node to your cluster that matches the specification in a `DaemonSet`,
+  the control plane schedules a `Pod` for that `DaemonSet` onto the new node.
+* [`Job`](/docs/concepts/workloads/controllers/job/) and
+  [`CronJob`](/docs/concepts/workloads/controllers/cron-jobs/)
+  define tasks that run to completion and then stop. Jobs represent one-off tasks, whereas
+  `CronJobs` recur according to a schedule.
 
-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.
+In the wider Kubernetes ecosystem, you can find third-party workload resources that provide
+additional behaviors. Using a
+[custom resource definition](/docs/concepts/extend-kubernetes/api-extension/custom-resources/),
+you can add in a third-party workload resource if you want a specific behavior that's not part
+of Kubernetes' core. For example, if you wanted to run a group of `Pods` for your application but
+stop work unless _all_ the Pods are available (perhaps for some high-throughput distributed task),
+then you can implement or install an extension that does provide that feature.
 
 ## {{% 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 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/)
+* [Run automated tasks with a `CronJob`](/docs/tasks/job/automated-tasks-with-cron-jobs/)
+
+To learn about Kubernetes' mechanisms for separating code from configuration,
+visit [Configuration](/docs/concepts/configuration/).
+
+There are two supporting concepts that provide backgrounds about how Kubernetes manages pods
+for applications:
+* [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.
 
 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).
+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.