docs: Update KubeletConfigDropinDir doc information

Signed-off-by: Sohan Kunkerkar <sohank2602@gmail.com>
Signed-off-by: Peter Hunt <pehunt@redhat.com>

content/en/docs/reference/node/kubelet-config-directory-merging.md

@@ -0,0 +1,155 @@
+---
+content_type: "reference"
+title: Kubelet Configuration Directory Merging
+weight: 50
+---
+
+When using the kubelet's `--config-dir` flag to specify a drop-in directory for
+configuration, there is some specific behavior on how different types are
+merged.
+
+Here are some examples of how different data types behave during configuration merging:
+
+### Structure Fields
+There are two types of structure fields in a YAML structure: singular (or a
+scalar type) and embedded (structures that contain scalar types).
+The configuration merging process handles the overriding of singular and embedded struct fields to create a resulting kubelet configuration.
+
+For instance, you may want a baseline kubelet configuration for all nodes, but you may want to customize the `address` and `authorization` fields.
+This can be done as follows:
+
+Main kubelet configuration file contents:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+port: 20250
+authorization:
+  mode: Webhook
+  webhook:
+    cacheAuthorizedTTL: "5m"
+    cacheUnauthorizedTTL: "30s"
+serializeImagePulls: false
+address: "192.168.0.1"
+```
+
+Contents of a file in `--config-dir` directory:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+authorization:
+  mode: AlwaysAllow
+  webhook:
+    cacheAuthorizedTTL: "8m"
+    cacheUnauthorizedTTL: "45s"
+address: "192.168.0.8"
+```
+
+The resulting configuration will be as follows:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+port: 20250
+serializeImagePulls: false
+authorization:
+  mode: AlwaysAllow
+  webhook:
+    cacheAuthorizedTTL: "8m"
+    cacheUnauthorizedTTL: "45s"
+address: "192.168.0.8"
+```
+
+### Lists
+You can overide the slices/lists values of the kubelet configuration.
+However, the entire list gets overridden during the merging process.
+For example, you can override the `clusterDNS` list as follows:
+
+Main kubelet configuration file contents:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+port: 20250
+serializeImagePulls: false
+clusterDNS:
+  - "192.168.0.9"
+  - "192.168.0.8"
+```
+
+Contents of a file in `--config-dir` directory:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+clusterDNS:
+  - "192.168.0.2"
+  - "192.168.0.3"
+  - "192.168.0.5"
+```
+
+The resulting configuration will be as follows:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+port: 20250
+serializeImagePulls: false
+clusterDNS:
+  - "192.168.0.2"
+  - "192.168.0.3"
+  - "192.168.0.5"
+```
+
+### Maps, including Nested Structures
+
+Individual fields in maps, regardless of their value types (boolean, string, etc.), can be selectively overridden.
+However, for `map[string][]string`, the entire list associated with a specific field gets overridden.
+Let's understand this better with an example, particularly on fields like `featureGates` and `staticPodURLHeader`:
+
+Main kubelet configuration file contents:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+port: 20250
+serializeImagePulls: false
+featureGates:
+  AllAlpha: false
+  MemoryQoS: true
+staticPodURLHeader:
+  kubelet-api-support:
+  - "Authorization: 234APSDFA"
+  - "X-Custom-Header: 123"
+  custom-static-pod:
+  - "Authorization: 223EWRWER"
+  - "X-Custom-Header: 456"
+```
+
+Contents of a file in `--config-dir` directory:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+featureGates:
+  MemoryQoS: false
+  KubeletTracing: true
+  DynamicResourceAllocation: true
+staticPodURLHeader:
+  custom-static-pod:
+  - "Authorization: 223EWRWER"
+  - "X-Custom-Header: 345"
+```
+
+The resulting configuration will be as follows:
+```yaml
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+port: 20250
+serializeImagePulls: false
+featureGates:
+  AllAlpha: false
+  MemoryQoS: false
+  KubeletTracing: true
+  DynamicResourceAllocation: true
+staticPodURLHeader:
+  kubelet-api-support:
+  - "Authorization: 234APSDFA"
+  - "X-Custom-Header: 123"
+  custom-static-pod:
+  - "Authorization: 223EWRWER"
+  - "X-Custom-Header: 345"
+```