Add supported-versions doc (#1701)

* Add supported-versions doc

Signed-off-by: Flynn <[email protected]>

* Tweaks

Signed-off-by: Flynn <[email protected]>

* Update with minimum versions pulled from Helm charts. Update maxima per logicminds on GitHub, thanks!

Signed-off-by: Flynn <[email protected]>

* Reference K8s versions from install & upgrade task documentation.

Signed-off-by: Flynn <[email protected]>

* Whoops, fix links.

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* Fix greater-than.

Signed-off-by: Flynn <[email protected]>

* Drop 2.10 & 2.11 to K8s 1.23.

Signed-off-by: Flynn <[email protected]>

---------

Signed-off-by: Flynn <[email protected]>

linkerd.io/content/2.14/getting-started/_index.md

@@ -89,6 +89,10 @@ You should see the CLI version, and also `Server version: unavailable`. This is
 because you haven't installed the control plane on your cluster. Don't
 worry—we'll fix that soon enough.
 
+Make sure that your Linkerd version and Kubernetes version are compatible by
+checking Linkerd's [supported Kubernetes
+versions](../reference/k8s-versions/).
+
 ## Step 2: Validate your Kubernetes cluster
 
 Kubernetes clusters can be configured in many different ways. Before we can

linkerd.io/content/2.14/reference/k8s-versions.md

@@ -0,0 +1,31 @@
++++
+title = "Supported Kubernetes Versions"
+description = "Reference documentation for which Linkerd version supports which Kubernetes version"
++++
+
+Linkerd supports all versions of Kubernetes that were supported at the time
+that a given Linkerd version ships. For example, at the time that Linkerd
+stable-2.14.0 shipped, Kubernetes versions 1.26, 1.27, and 1.28 were
+supported, so Linkerd stable-2.14.0 supports all of those Kubernetes versions.
+(In many cases, as you'll see below, Linkerd versions will also support older
+Kubernetes versions.)
+
+Obviously, Linkerd stable-2.14.0 has no knowledge of what changes will come
+_after_ Kubernetes 1.28. In some cases, later versions of Kubernetes end up
+making changes that cause older versions of Linkerd to not work: we will
+update the chart below as these situations arise.
+
+| Linkerd Version | Minimum Kubernetes Version | Maximum Kubernetes Version |
+|-----------------|----------------------------|----------------------------|
+| `stable-2.10`   | `1.16`                     | `1.23`                     |
+| `stable-2.11`   | `1.17`                     | `1.23`                     |
+| `stable-2.12`   | `1.21`                     | `1.24`                     |
+| `stable-2.13`   | `1.21`                     | `1.28`                     |
+| `stable-2.14`   | `1.21`                     | `1.28`                     |
+
+Notes:
+
+1. Linkerd will almost never change the supported Kubernetes version in a
+   minor release, which is why the table above only lists major versions. One
+   known exception: Linkerd 2.11.0 supported Kubernetes 1.16, but 2.11.1 and
+   later required Kubernetes 1.17 as shown in the table above.

linkerd.io/content/2.14/tasks/install.md

@@ -29,6 +29,10 @@ Linkerd requires a Kubernetes cluster on which to run. Where this cluster lives
 is not important: it might be hosted on a cloud provider, may be running on your
 local machine, or even somewhere else.
 
+Make sure that your Linkerd version and Kubernetes version are compatible by
+checking Linkerd's [supported Kubernetes
+versions](../../reference/k8s-versions/).
+
 Before installing the control plane, validate that this Kubernetes cluster is
 configured appropriately for Linkerd by running:
 

linkerd.io/content/2.14/tasks/upgrade.md

@@ -44,8 +44,8 @@ restrictions.
 minor version within the same major version. In other words, if you are
 currently running version *2.x.y*, upgrading to *2.x.z*, where *z* is the latest
 minor version for major version *x*, is safe. This is true even if you would
-skip intermediate intermediate minor versions, i.e. it is still safe even if *z
-> y + 1*.
+skip intermediate intermediate minor versions, i.e. it is still safe even if
+*z* > *y + 1*.
 
 **To the next major version**. It is usually safe to upgrade to the latest minor
 version of the *next* major version. In other words, if you are currently
@@ -88,6 +88,10 @@ of Linkerd is healthy, e.g. by using `linkerd check`. For major version
 upgrades, you should also ensure that your data plane is up-to-date, e.g.
 with `linkerd check --proxy`, to avoid unintentional version skew.
 
+Make sure that your Linkerd version and Kubernetes version are compatible by
+checking Linkerd's [supported Kubernetes
+versions](../../reference/k8s-versions/).
+
 ## Upgrading the CLI
 
 The CLI can be used to validate whether Linkerd was installed correctly.