review prometheus docs

examples/customization/custom-vts-metrics-prometheus/nginx/README.md

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+# Deploying the Nginx Ingress controller
+
+This example aims to demonstrate the deployment of an nginx ingress controller and use a ConfigMap to enable [nginx vts module](github.com/vozlt/nginx-module-vts
+) to export metrics in prometheus format. 
+
+# vts-metrics 
+
+Vts-metrics export NGINX metrics. To deploy all the files simply run `kubectl apply -f nginx`. A deployment and service will be
+created which already has a `prometheus.io/scrape: 'true'` annotation and if you added
+the recommended Prometheus service-endpoint scraping [configuration](https://raw.githubusercontent.com/prometheus/prometheus/master/documentation/examples/prometheus-kubernetes.yml),
+Prometheus will scrape it automatically and you start using the generated metrics right away.
+
+## Default Backend
+
+The default backend is a Service capable of handling all url paths and hosts the
+nginx controller doesn't understand. This most basic implementation just returns
+a 404 page:
+
+```console
+$ kubectl apply -f default-backend.yaml
+deployment "default-http-backend" created
+service "default-http-backend" created
+
+$ kubectl -n kube-system get po
+NAME                                    READY     STATUS    RESTARTS   AGE
+default-http-backend-2657704409-qgwdd   1/1       Running   0          28s
+```
+
+## Custom configuration
+
+```console
+$ cat nginx-vts-metrics-conf.yaml
+apiVersion: v1
+data:
+  enable-vts-status: "true"
+kind: ConfigMap
+metadata:
+  name: nginx-vts-metrics-conf
+  namespace: kube-system
+```
+
+```console
+$ kubectl create -f nginx-vts-metrics-conf.yaml
+```
+
+## Controller
+
+You can deploy the controller as follows:
+
+```console
+$ kubectl apply -f nginx-ingress-controller.yaml
+deployment "nginx-ingress-controller" created
+
+$ kubectl -n kube-system get po
+NAME                                       READY     STATUS    RESTARTS   AGE
+default-http-backend-2657704409-qgwdd      1/1       Running   0          2m
+nginx-ingress-controller-873061567-4n3k2   1/1       Running   0          42s
+```
+
+## Result
+Check whether the ingress controller successfully generated the NGINX vts status:
+```console
+$ kubectl exec nginx-ingress-controller-873061567-4n3k2 -n kube-system cat /etc/nginx/nginx.conf|grep vhost_traffic_status_display
+ vhost_traffic_status_display;
+ vhost_traffic_status_display_format html;
+```
+### NGINX vts dashboard
+The vts dashboard provides real time metrics. 
+
+![vts dashboard](imgs/vts-dashboard.png)
+
+Because the vts port it's not yet exposed, you should forward the controller port to see it.
+
+```console
+$ kubectl port-forward $(kubectl get pods --selector=k8s-app=nginx-ingress-controller -n kube-system --output=jsonpath={.items..metadata.name}) -n kube-system 18080
+```
+
+Now open the url [http://localhost:18080/nginx_status](http://localhost:18080/nginx_status) in your browser.
+
+
+### Prometheus metrics output
+NGINX Ingress controller already has a parser to convert vts metrics to Prometheus format. It exports prometheus metrics to the address `:10254/metrics`.
+
+```console
+$ kubectl exec -ti -n kube-system $(kubectl get pods --selector=k8s-app=nginx-ingress-controller -n kube-system --output=jsonpath={.items..metadata.name}) curl localhost:10254/metrics
+ingress_controller_ssl_expire_time_seconds{host="foo.bar.com"} -6.21355968e+10
+# HELP ingress_controller_success Cumulative number of Ingress controller reload operations
+# TYPE ingress_controller_success counter
+ingress_controller_success{count="reloads"} 3
+# HELP nginx_bytes_total Nginx bytes count
+# TYPE nginx_bytes_total counter
+nginx_bytes_total{direction="in",ingress_class="nginx",namespace="",server_zone="*"} 3708
+nginx_bytes_total{direction="in",ingress_class="nginx",namespace="",server_zone="_"} 3708
+nginx_bytes_total{direction="out",ingress_class="nginx",namespace="",server_zone="*"} 5256
+nginx_bytes_total{direction="out",ingress_class="nginx",namespace="",server_zone="_"} 5256
+```
+
+### Customize metrics
+
+The default [vts vhost key](https://github.com/vozlt/nginx-module-vts#vhost_traffic_status_filter_by_set_key) is `$geoip_country_code country::*` that expose metrics groupped by server and country code. The example below show how to have metrics grouped by server and server path.
+
+![vts dashboard](imgs/vts-dashboard-filter-key-path.png)
+
+##  NGINX custom configuration ( http level )
+
+```
+  apiVersion: v1
+  kind: ConfigMap
+  data:
+    enable-vts-status: "true"
+    vts-default-filter-key: "$server_name"
+...
+```
+
+## Customize ingress
+
+```
+ apiVersion: extensions/v1beta1
+  kind: Ingress
+  metadata:
+    annotations:
+      ingress.kubernetes.io/vts-filter-key: $uri $server_name
+    name: ingress
+```
+
+## Result 
+
+![prometheus filter key path](imgs/prometheus-filter-key-path.png)