docs: Grafana Dashboard Configuration (#731)

docs/en/latest/plugins/prometheus.md

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+---
+title: prometheus
+---
+
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+
+This guide shows how to monitor Apache APISIX Ingress Controller using Prometheus and Grafana.
+
+## Enable Prometheus
+
+Use CRD file to enable Prometheus in global configurations. The definition file for custom resources is `ApisixClusterConfig`, so the configuration should be:
+
+```yaml
+apiVersion: apisix.apache.org/v2beta3
+kind: ApisixClusterConfig
+metadata:
+  name: default
+spec:
+  monitoring:
+    prometheus:
+      enable: true
+```
+
+## Configure Prometheus Server
+
+The Prometheus server address should be `127.0.0.1:9090` by default. You can set the target url for `apisix-ingress-controller` manually in `prometheus.yml`.
+For example:
+
+```yaml
+...
+scrape_configs:
+  - job_name: "apisix-ingress-controller"
+    static_configs:
+    - targets: ["localhost:9092"]
+```
+
+According to the above example, the metrics are exposed in `http://localhost:9092/metrics` now.  
+Visit `http://localhost:9090` in your browser, and select `apisix-ingress-controller` in `targets`
+or visit `http://localhost:9092/metrics` to see the data.
+![metrics_data.png](../../../assets/images/metrics_data.png)
+
+## Grafana Dashboard
+
+Grafana dashboard shows the metrics exposed in Prometheus graphically.  
+[Installing Grafana](https://grafana.com/docs/grafana/latest/#installing-grafana)  
+Visit `http://localhost:3000/` in your browser to access Grafana. The default username and password are `admin`.
+Then create a new dashboard for `apisix-ingress-controller`.  
+![grafana.png](../../../assets/images/grafana.png)  
+Follow the steps to apply the configuration of Grafana Dashboard for `apisix-ingress-controller`.
+
+- Add an empty panel, and import via panel json in `apisix-ingress-controller/docs/assets/other/json/apisix-ingress-controller-grafana.json`.
+![img.png](../../../assets/images/img.png)
+![import_via_panel_json.png](../../../assets/images/import_via_panel_json.png)
+- Select `Prometheus database` as the datasource. Set the URL according to your Prometheus server configuration.  
+![datasource_1.png](../../../assets/images/datasource_1.png)
+![datasource_2.png](../../../assets/images/datasource_2.png)
+
+### Preview
+
+![dashboard_view_1.png](../../../assets/images/dashboard_view_1.png)
+![dashboard_view_2.png](../../../assets/images/dashboard_view_2.png)
+![dashboard_view_3.png](../../../assets/images/dashboard_view_3.png)
+
+## Available metrics
+
+- `Is leader` A gauge type metric with value 0 or 1, indicates whether the role of controller instance is leader, for leader is 1 and candidate is 0.  
+Labels:
+  - controller_pod
+  - controller_namespace
+- `Status codes` status codes of requests to APISIX.  
+Labels:
+  - controller_pod
+  - controller_namespace
+  - status_code: the HTTP status code returned by APISIX.  
+  - resource
+- `Latency` Request latencies with APISIX.  
+Labels:
+  - controller_pod
+  - controller_namespace
+- `Requests` Number of requests to APISIX.  
+Labels:
+  - controller_pod
+  - controller_namespace
+  - resource
+- `Check cluster health` Number of cluster health check operations.  
+Labels:
+  - controller_pod
+  - controller_namespace
+  - name: cluster name.
+- `Sync operation` Number of sync operations.  
+Labels:
+  - controller_pod
+  - controller_namespace
+  - resource
+  - result: sync success or failure.
+- `Cache sync` Number of cache sync operations.  
+Labels:
+  - controller_pod
+  - controller_namespace
+  - result: sync success or failure.
+- `Controller events` Number of events handled by the controller.  
+Labels:
+  - controller_pod
+  - controller_namespace
+  - resource
+  - operation: includes `add`, `update`, `delete`.
+