[kubeforward] add to external plugin (#323)

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

Author: Paramoshka

content/explugins/kubeforward.md

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+title = "kubeforward"
+description = "*kubeforward* - dynamically updates DNS forwarders based on changes to a specified Kubernetes Service."
+weight = 10
+tags = ["plugin", "kubeforward", "kubernetes", "dns"]
+categories = ["plugin", "external"]
+date = "2025-04-04T17:15:00+00:00"
+repo = "https://github.com/deckhouse/coredns-kubeforward"
+home = "https://github.com/deckhouse/coredns-kubeforward/blob/main/README.md"
++++
+
+## Description
+
+The **kubeforward** plugin enables CoreDNS to dynamically update its list of DNS forwarders by monitoring changes to a specified Kubernetes Service. It observes `EndpointSlices` associated with the Service and adjusts the DNS forwarding configuration in real-time as endpoints are added, removed, or updated. This functionality enhances the reliability and resilience of DNS services within Kubernetes clusters.
+
+## Syntax
+
+```txt
+kubeforward {
+    namespace <namespace>
+    service_name <service_name>
+    port_name <port_name>
+    expire <duration>
+    health_check <duration>
+    force_tcp
+    prefer_udp
+}
+```
+
+## Configuration Parameters
+
+- `namespace` (required): Specifies the Kubernetes namespace where the target Service resides.
+
+- `service_name` (required): The name of the Service to monitor for endpoint changes.
+
+- `port_name`: The name of the port in the Service resource responsible for handling DNS queries.
+
+- `expire`: Duration after which cached connections expire. Default is 10s.
+
+- `health_check`: Interval for performing health checks on upstream servers. Default is 0.5s.
+
+- `force_tcp`: Forces the use of TCP for forwarding queries.
+
+- `prefer_udp`: Prefers the use of UDP for forwarding queries.
+
+## Examples
+
+```
+.:53 {
+    errors
+    log
+    kubeforward {
+        namespace kube-system
+        service_name kube-dns
+        port_name dns
+        expire 10m
+        health_check 5s
+        prefer_udp
+        force_tcp
+    }
+}
+```
+
+## Limitations
+
+Limited Support for Forward Plugin Options: The plugin utilizes the functionality of the forward plugin for serving DNS under the hood but does not support the full list of classic forward options due to the lack of a public interface for configuring options.
+
+
+