Clearer information about the emptyDir and correction for how topolog…

…yKey works (#42780)

* removes "tmpfs is cleared on node reboot"

I believe the statement is confusing since we are in the emptyDir section of the documentation.  

If a Node is restarted then all pods that resided on that node will be rescheduled onto another Node.  Rescheduled pods will have an empty volume  whether you choose emptyDir.medium "Memory" or not.

* removes bad comma

* improves memory limit description

Co-authored-by: Tim Bannister <[email protected]>

* removes incorrect explanation for topologyKey in an affinity or anti-affinity rule (#1)

The existing text does not make sense to me.  

There is no zone "V" or "R" in the example.  

I have changed the text to be consistent with top answer here which seems to make more sense: https://stackoverflow.com/questions/72240224/what-is-topologykey-in-pod-affinity

* gives more context to node label configuration

* manually wraps text and replaces absolute links with relative ones

* Update assign-pod-node.md

---------

Co-authored-by: Tim Bannister <[email protected]>
Co-authored-by: Qiming Teng <[email protected]>

content/en/docs/concepts/scheduling-eviction/assign-pod-node.md

@@ -35,8 +35,10 @@ specific Pods:
 ## Node labels {#built-in-node-labels}
 
 Like many other Kubernetes objects, nodes have
-[labels](/docs/concepts/overview/working-with-objects/labels/). You can [attach labels manually](/docs/tasks/configure-pod-container/assign-pods-nodes/#add-a-label-to-a-node).
-Kubernetes also populates a [standard set of labels](/docs/reference/node/node-labels/) on all nodes in a cluster.
+[labels](/docs/concepts/overview/working-with-objects/labels/). You can
+[attach labels manually](/docs/tasks/configure-pod-container/assign-pods-nodes/#add-a-label-to-a-node).
+Kubernetes also populates a [standard set of labels](/docs/reference/node/node-labels/)
+on all nodes in a cluster.
 
 {{<note>}}
 The value of these labels is cloud provider specific and is not guaranteed to be reliable.
@@ -303,17 +305,23 @@ Pod affinity rule uses the "hard"
 `requiredDuringSchedulingIgnoredDuringExecution`, while the anti-affinity rule
 uses the "soft" `preferredDuringSchedulingIgnoredDuringExecution`.
 
-The affinity rule says that the scheduler can only schedule a Pod onto a node if
-the node is in the same zone as one or more existing Pods with the label
-`security=S1`. More precisely, the scheduler must place the Pod on a node that has the
-`topology.kubernetes.io/zone=V` label, as long as there is at least one node in
-that zone that currently has one or more Pods with the Pod label `security=S1`.
-
-The anti-affinity rule says that the scheduler should try to avoid scheduling
-the Pod onto a node that is in the same zone as one or more Pods with the label
-`security=S2`. More precisely, the scheduler should try to avoid placing the Pod on a node that has the
-`topology.kubernetes.io/zone=R` label if there are other nodes in the
-same zone currently running Pods with the `Security=S2` Pod label.
+The affinity rule specifies that the scheduler is allowed to place the example Pod 
+on a node only if that node belongs to a specific [zone](/docs/concepts/scheduling-eviction/topology-spread-constraints/topology-spread-constraints/)
+where other Pods have been labeled with `security=S1`. 
+For instance, if we have a cluster with a designated zone, let's call it "Zone V," 
+consisting of nodes labeled with `topology.kubernetes.io/zone=V`, the scheduler can 
+assign the Pod to any node within Zone V, as long as there is at least one Pod within 
+Zone V already labeled with `security=S1`. Conversely, if there are no Pods with `security=S1` 
+labels in Zone V, the scheduler will not assign the example Pod to any node in that zone.
+
+The anti-affinity rule specifies that the scheduler should try to avoid scheduling the Pod 
+on a node if that node belongs to a specific [zone](/docs/concepts/scheduling-eviction/topology-spread-constraints/topology-spread-constraints/)
+where other Pods have been labeled with `security=S2`. 
+For instance, if we have a cluster with a designated zone, let's call it "Zone R," 
+consisting of nodes labeled with `topology.kubernetes.io/zone=R`, the scheduler should avoid 
+assigning the Pod to any node within Zone R, as long as there is at least one Pod within 
+Zone R already labeled with `security=S2`. Conversely, the anti-affinity rule does not impact 
+scheduling into Zone R if there are no Pods with `security=S2` labels.
 
 To get yourself more familiar with the examples of Pod affinity and anti-affinity,
 refer to the [design proposal](https://git.k8s.io/design-proposals-archive/scheduling/podaffinity.md).
@@ -327,7 +335,8 @@ to learn more about how these work.
 In principle, the `topologyKey` can be any allowed label key with the following
 exceptions for performance and security reasons:
 
-- For Pod affinity and anti-affinity, an empty `topologyKey` field is not allowed in both `requiredDuringSchedulingIgnoredDuringExecution`
+- For Pod affinity and anti-affinity, an empty `topologyKey` field is not allowed in both
+  `requiredDuringSchedulingIgnoredDuringExecution`
   and `preferredDuringSchedulingIgnoredDuringExecution`.
 - For `requiredDuringSchedulingIgnoredDuringExecution` Pod anti-affinity rules,
   the admission controller `LimitPodHardAntiAffinityTopology` limits

content/en/docs/concepts/storage/volumes.md

@@ -245,9 +245,8 @@ The `emptyDir.medium` field controls where `emptyDir` volumes are stored. By
 default `emptyDir` volumes are stored on whatever medium that backs the node
 such as disk, SSD, or network storage, depending on your environment. If you set
 the `emptyDir.medium` field to `"Memory"`, Kubernetes mounts a tmpfs (RAM-backed
-filesystem) for you instead.  While tmpfs is very fast, be aware that unlike
-disks, tmpfs is cleared on node reboot and any files you write count against
-your container's memory limit.
+filesystem) for you instead.  While tmpfs is very fast be aware that, unlike
+disks, files you write count against the memory limit of the container that wrote them.
 
 
 A size limit can be specified for the default medium, which limits the capacity