Add Grafana Dashboard for NGINX metrics

Author: Rulox

README.md

@@ -140,6 +140,9 @@ Note: the binary is built for the OS/arch of your machine. To build binaries for
 
 The binary is built with the name `nginx-prometheus-exporter`.
 
+## Grafana Dashboard
+The official Grafana dashboard is provided with the exporter for NGINX. Check the [Grafana Dashboard](./grafana/README.md) documentation for more information.
+
 ## Support
 
 The commercial support is available for NGINX Plus customers when the NGINX Prometheus Exporter is used with NGINX Ingress Controller.

grafana/README.md

@@ -0,0 +1,35 @@
+# Grafana Dashboard
+We provide the official Grafana dashboard that visualizes the NGINX metrics exposed by the exporter. The dashboard allows you to filter metrics per instance or see the metrics from all instances.
+
+## Prerequisites
+
+The dashboard has been tested with the following software versions:
+
+* NGINX Prometheus Exporter >= 0.4.1
+* Grafana >= v5.0.0
+* Prometheus >= v2.0.0
+
+A Prometheus data source needs to be [added](https://prometheus.io/docs/visualization/grafana/#using) before installing the dashboard.
+
+## Installing the Dashboard
+
+In the Grafana UI complete the following steps:
+
+1. Use the *New Dashboard* button and click *Import*.
+2. Upload `dashboard.json` or copy and paste the contents of the file in the textbox and click *Load*.
+3. Set the Prometheus data source and click *Import*.
+4. The dashboard will appear. Note how you can filter the instance label just below the dashboard title (top left corner). This allows you to filter metrics per instance. By default, all instances are selected.
+
+![dashboard](./dashboard.png)
+
+## Graphs
+
+The dashboard comes with 2 rows with the following graphs for NGINX metrics:
+
+* Status
+  * Up/Down graph per instance. It shows the `nginx_up` metric.
+* Metrics
+  * Processed connections (`nginx_connections_accepted` and `nginx_connections_handled` metrics). This graph shows an [irate](https://prometheus.io/docs/prometheus/latest/querying/functions/#irate) in a range of 5 minutes. Useful for seeing the variation of the processed connections in time. 
+  * Active connections (`nginx_connections_active`, `nginx_connections_reading`, `nginx_connections_waiting` and `nginx_connections_writing`). Useful for checking what is happening right now.
+  * Total Requests with an irate (5 minutes range too) of the total number of client requests (`nginx_http_requests_total`) over time.
+