Add concept page about Controllers (#15733)

* Add controller concept

* Fix controller glossary entries

* Link from Understanding Kubernetes Objects to Controllers

content/en/docs/concepts/workloads/controllers/cron-jobs.md

@@ -36,7 +36,7 @@ If `startingDeadlineSeconds` is set to a large value or left unset (the default)
 and if `concurrencyPolicy` is set to `Allow`, the jobs will always run
 at least once.
 
-For every CronJob, the CronJob controller checks how many schedules it missed in the duration from its last scheduled time until now. If there are more than 100 missed schedules, then it does not start the job and logs the error
+For every CronJob, the CronJob {{< glossary_tooltip term_id="controller" >}} checks how many schedules it missed in the duration from its last scheduled time until now. If there are more than 100 missed schedules, then it does not start the job and logs the error
 
 ````
 Cannot determine if job needs to be started. Too many missed start time (> 100). Set or decrease .spec.startingDeadlineSeconds or check clock skew.

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

@@ -86,10 +86,10 @@ When the two are specified the result is ANDed.
 If the `.spec.selector` is specified, it must match the `.spec.template.metadata.labels`. Config with these not matching will be rejected by the API.
 
 Also you should not normally create any Pods whose labels match this selector, either directly, via
-another DaemonSet, or via other controller such as ReplicaSet.  Otherwise, the DaemonSet
-controller will think that those Pods were created by it.  Kubernetes will not stop you from doing
-this.  One case where you might want to do this is manually create a Pod with a different value on
-a node for testing.
+another DaemonSet, or via another workload resource such as ReplicaSet.  Otherwise, the DaemonSet
+{{< glossary_tooltip term_id="controller" >}} will think that those Pods were created by it.
+Kubernetes will not stop you from doing this. One case where you might want to do this is manually
+create a Pod with a different value on a node for testing.
 
 ### Running Pods on Only Some Nodes
 

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

@@ -13,10 +13,10 @@ weight: 30
 
 {{% capture overview %}}
 
-A _Deployment_ controller provides declarative updates for [Pods](/docs/concepts/workloads/pods/pod/) and
+A _Deployment_ provides declarative updates for [Pods](/docs/concepts/workloads/pods/pod/) and
 [ReplicaSets](/docs/concepts/workloads/controllers/replicaset/).
 
-You describe a _desired state_ in a Deployment, and the Deployment controller changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.
+You describe a _desired state_ in a Deployment, and the Deployment {{< glossary_tooltip term_id="controller" >}} changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.
 
 {{< note >}}
 Do not manage ReplicaSets owned by a Deployment. Consider opening an issue in the main Kubernetes repository if your use case is not covered below.

content/en/docs/concepts/workloads/controllers/jobs-run-to-completion.md

@@ -173,10 +173,10 @@ parallelism, for a variety of reasons:
 - For _fixed completion count_ Jobs, the actual number of pods running in parallel will not exceed the number of
   remaining completions.   Higher values of `.spec.parallelism` are effectively ignored.
 - For _work queue_ Jobs, no new Pods are started after any Pod has succeeded -- remaining Pods are allowed to complete, however.
-- If the controller has not had time to react.
-- If the controller failed to create Pods for any reason (lack of `ResourceQuota`, lack of permission, etc.),
+- If the Job {{< glossary_tooltip term_id="controller" >}} has not had time to react.
+- If the Job controller failed to create Pods for any reason (lack of `ResourceQuota`, lack of permission, etc.),
   then there may be fewer pods than requested.
-- The controller may throttle new Pod creation due to excessive previous pod failures in the same Job.
+- The Job controller may throttle new Pod creation due to excessive previous pod failures in the same Job.
 - When a Pod is gracefully shut down, it takes time to stop.
 
 ## Handling Pod and Container Failures

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

@@ -32,7 +32,7 @@ ReplicaSet's identifying information within their ownerReferences field. It's th
 knows of the state of the Pods it is maintaining and plans accordingly.
 
 A ReplicaSet identifies new Pods to acquire by using its selector. If there is a Pod that has no OwnerReference or the
-OwnerReference is not a controller and it matches a ReplicaSet's selector, it will be immediately acquired by said
+OwnerReference is not a {{< glossary_tooltip term_id="controller" >}} and it matches a ReplicaSet's selector, it will be immediately acquired by said
 ReplicaSet.
 
 ## When to use a ReplicaSet

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

@@ -32,8 +32,8 @@ following.
 
 In the above, stable is synonymous with persistence across Pod (re)scheduling.
 If an application doesn't require any stable identifiers or ordered deployment,
-deletion, or scaling, you should deploy your application with a controller that
-provides a set of stateless replicas. Controllers such as
+deletion, or scaling, you should deploy your application using a workload object
+that provides a set of stateless replicas.
 [Deployment](/docs/concepts/workloads/controllers/deployment/) or
 [ReplicaSet](/docs/concepts/workloads/controllers/replicaset/) may be better suited to your stateless needs.
 
@@ -164,8 +164,9 @@ This must be done manually.
 
 ### Pod Name Label
 
-When the StatefulSet controller creates a Pod, it adds a label, `statefulset.kubernetes.io/pod-name`, 
-that is set to the name of the Pod. This label allows you to attach a Service to a specific Pod in 
+When the StatefulSet {{< glossary_tooltip term_id="controller" >}} creates a Pod,
+it adds a label, `statefulset.kubernetes.io/pod-name`, that is set to the name of
+the Pod. This label allows you to attach a Service to a specific Pod in
 the StatefulSet.
 
 ## Deployment and Scaling Guarantees