Expose NGINX Plus dashboard (nginx#1488)

* Expose NGINX Plus dashboard

Problem: As a user, I want observability into the NGINX Plus configuration and metrics.

Solution: By exposing the NGINX Plus dashboard, a user can easily visualize real-time metrics and information about the configuration.

* Code review comments

* Reapply allow/deny; fix image tag

* Arch note

Author: miledxz

internal/mode/static/nginx/conf/nginx-plus.conf

@@ -26,6 +26,21 @@ http {
   sendfile on;
   tcp_nopush on;
 
+  server {
+    listen 127.0.0.1:8765;
+    root /usr/share/nginx/html;
+    access_log off;
+
+    allow 127.0.0.1;
+    deny all;
+
+    location = /dashboard.html {}
+
+    location /api {
+      api write=off;
+    }
+  }
+
   server {
     listen unix:/var/run/nginx/nginx-plus-api.sock;
     access_log off;

site/content/how-to/monitoring/dashboard.md

@@ -0,0 +1,30 @@
+---
+title: "NGINX Plus Dashboard"
+description: "Learn how to view the NGINX Plus dashboard to see real-time metrics."
+weight: 200
+toc: true
+docs: "DOCS-000"
+---
+
+{{<custom-styles>}}
+
+## Overview
+
+The NGINX Plus dashboard offers a real-time live activity monitoring interface that shows key load and performance metrics of your server infrastructure. The dashboard is enabled by default for NGINX Gateway Fabric deployments that use NGINX Plus as the data plane. The dashboard is available on port 8765.
+
+To access the dashboard:
+
+1. Use port-forwarding to forward connections to port 8765 on your local machine to port 8765 on the NGINX Gateway Fabric pod (replace `<nginx-gateway-fabric-pod>` with the actual name of the pod).
+
+    ```shell
+    kubectl port-forward <nginx-gateway-fabric-pod> 8765:8765 -n nginx-gateway
+    ```
+
+1. Open your browser to [http://127.0.0.1:8765/dashboard.html](http://127.0.0.1:8765/dashboard.html) to access the dashboard.
+
+The dashboard will look like this:
+
+{{<img src="img/nginx-plus-dashboard.png" alt="">}}
+
+
+{{< note >}}The [API](https://nginx.org/en/docs/http/ngx_http_api_module.html), which the dashboard uses to get the metrics, is also accessible using the `/api` path.{{< /note >}}

site/content/how-to/monitoring/monitoring.md renamed to site/content/how-to/monitoring/prometheus.md

@@ -1,6 +1,6 @@
 ---
-title: "Monitoring NGINX Gateway Fabric"
-description: "Learn how to monitor your NGINX Gateway Fabric effectively. This guide provides easy steps for configuring monitoring settings and understanding key performance metrics."
+title: "Prometheus Metrics"
+description: "Learn how to monitor your NGINX Gateway Fabric effectively. This guide provides easy steps for configuring and understanding key performance metrics using Prometheus."
 weight: 100
 toc: true
 docs: "DOCS-000"

site/content/how-to/monitoring/troubleshooting.md

@@ -1,7 +1,7 @@
 ---
 title: "Troubleshooting"
 
-weight: 200
+weight: 300
 toc: true
 docs: "DOCS-000"
 ---

site/content/overview/gateway-architecture.md

@@ -92,6 +92,12 @@ The following list describes the connections, preceeded by their types in parent
 1. (HTTP, HTTPS) A _client_ sends traffic to and receives traffic from any of the _NGINX workers_ on ports 80 and 443.
 1. (HTTP, HTTPS) An _NGINX worker_ sends traffic to and receives traffic from the _backends_.
 
+### Differences with NGINX Plus
+
+The previous diagram depicts NGINX Gateway Fabric using NGINX Open Source. NGINX Gateway Fabric with NGINX Plus has the following difference:
+
+- An _admin_ can connect to the NGINX Plus API using port 8765. NGINX only allows connections from localhost.
+
 ## Pod readiness
 
 The `nginx-gateway` container includes a readiness endpoint available through the path `/readyz`. A [readiness probe](https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/#define-readiness-probes) periodically checks the endpoint on startup, returning a `200 OK` response when the pod can accept traffic for the data plane. Once the control plane successfully starts, the pod becomes ready.