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

content/en/docs/reference/node/kubelet-files.md

@@ -1,17 +1,19 @@
 ---
 content_type: "reference"
-title: Files written and read by the kubelet
+title: Local Files And Paths Used By The Kubelet
 weight: 42
 ---
 
 The {{< glossary_tooltip text="kubelet" term_id="kubelet" >}} is mostly a stateless
 process running on a Kubernetes {{< glossary_tooltip text="node" term_id="node" >}}.
 This document outlines files that kubelet reads and writes.
 
-Kubelet uses the {{< glossary_tooltip text="control plane" term_id="control-plane" >}} as
+The kubelet typically uses the {{< glossary_tooltip text="control plane" term_id="control-plane" >}} as
 the source of truth on what needs to run on the Node, and the
 {{<glossary_tooltip text="container runtime" term_id="container-runtime">}} to retrieve
-the current state of containers. Kubelet also relies on reading
+the current state of containers. So long as you provide a _kubeconfig_ (API client configuration)
+to the kubelet, the kubelet does connect to your control plane; otherwise the node operates in
+_standalone mode_. On Linux the kubelet also relies on reading
 cgroups and various system files to collect metrics. However, there are still a few other files
 that are used by the kubelet.
 
@@ -50,8 +52,9 @@ Location can be configured using the `staticPodPath` kubelet configuration optio
 #### Checkpoint files
 
 All resource managers keep the mapping of Pods to allocated resources in state files.
-State files located in the kubelet's root directory,
-typically `/var/lib/kubelet`. Kubelet root directory can be configured
+State files are located in the kubelet's base directory, also termed the _root directory_
+(but not the same as `/`, the node root directory). You can configure the base directory
+for the kubelet
 using the kubelet command line argument `--root-dir`.
 
 Names of files:
@@ -61,17 +64,19 @@ Names of files:
 - `kubelet_internal_checkpoint` for Device Manager
 - `dra_manager_state` for DRA
 
-#### Pod Status checkpoint
+#### Pod status checkpoint storage {#pod-status-manager-state}
 
 {{< feature-state feature_gate_name="InPlacePodVerticalScaling" >}}
 
 The pod status is being checkpointed to implement the Pod resize feature.
-The file name is `pod_status_manager_state` in kubelet root directory
-(`/var/lib/kubelet` or configure using `--root-dir`).
+The file name is `pod_status_manager_state` within the kubelet base directory
+(`/var/lib/kubelet` by default on Linux; configurable using `--root-dir`).
 
 ### Sockets
 
-Kubelet opens a few sockets as well as reading some other sockets.
+The kubelet communicates using local Unix-domain sockets. Some are sockets that the
+kubelet listens on, and for other sockets the kubelet discovers them and then connects
+as a client.
 
 #### Container runtime
 
@@ -85,24 +90,35 @@ The actual values of those endpoints depend on the container runtime being used.
 
 #### Device plugins
 
-Kubelet exposes socket `/var/lib/kubelet/device-plugins/kubelet.sock` for
+The kubelet exposes a socket at the path `/var/lib/kubelet/device-plugins/kubelet.sock` for
 various [Device Plugins to register](/docs/concepts/extend-kubernetes/compute-storage-net/device-plugins/#device-plugin-implementation).
 
 When a device plugin registers itself, it provides its socket path for the kubelet to connect.
 
-The device plugin socket should be in the directory `/var/lib/kubelet/device-plugins`.
+The device plugin socket should be in the directory `device-plugins` within the kubelet base
+directory. On a typical Linux node, this means `/var/lib/kubelet/device-plugins`.
 
-#### Pod Resources API
+#### Pod resources API
 
 [Pod Resources API](/docs/concepts/extend-kubernetes/compute-storage-net/device-plugins/#monitoring-device-plugin-resources)
-will be exposed at the address `/var/lib/kubelet/pod-resources`.
+will be exposed at the path `/var/lib/kubelet/pod-resources`.
 
 #### DRA and CSI plugins
 
-DRA and CSI plugins are located in `plugins_registry` in kubelet's root directory
+The kubelet looks for socket files created by device or storage plugins, and then attempts to connect
+to these sockets. The directory that the kubelet looks in is `plugins_registry` within the kubelet base
+directory, so on a typical Linux node this means `/var/lib/kubelet/plugins_registry`.
+
+The types of plugins that can place socket files into that directory are:
+
+- CSI plugins
+- DRA plugins
 (typically `/var/lib/kubelet/plugins_registry`).
 
-### Utility
+### Locking
+
+{{< feature-state state="alpha" for_k8s_version="v1.2" >}}
+
 
 Kubelet lock file, typically `/var/run/kubelet.lock`,
 can be configured using the `--lock-file` kubelet command line argument.