Update the Alerting HA docs (#60292)

* Update the Alerting HA docs

* Update docs/sources/alerting/set-up/configure-high-availability/_index.md

Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

* Update docs/sources/alerting/set-up/configure-high-availability/_index.md

Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

* Update docs/sources/alerting/set-up/configure-high-availability/_index.md

Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

* Update docs/sources/alerting/set-up/configure-high-availability/_index.md

Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

* Update docs/sources/alerting/set-up/configure-high-availability/_index.md

Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

* Update HA introduction paragraph

* Apply prettier

Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

docs/sources/alerting/set-up/configure-high-availability/_index.md

@@ -15,9 +15,9 @@ weight: 300
 
 # Enable alerting high availability
 
-You can enable alerting high availability support by updating the Grafana configuration file. On Kubernetes, you can enable alerting high availability by updating the Kubernetes container definition.
+You can enable alerting high availability support by updating the Grafana configuration file. If you run Grafana in a Kubernetes cluster, additional steps are required. Both options are described below.
 
-## Update Grafana configuration file
+## Enable alerting high availability in Grafana
 
 ### Before you begin
 
@@ -31,9 +31,9 @@ Since gossiping of notifications and silences uses both TCP and UDP port `9094`,
 3. Set `[ha_listen_address]` to the instance IP address using a format of `host:port` (or the [Pod's](https://kubernetes.io/docs/concepts/workloads/pods/) IP in the case of using Kubernetes).
    By default, it is set to listen to all interfaces (`0.0.0.0`).
 
-## Update Kubernetes container definition
+## Enable alerting high availability using Kubernetes
 
-If you are using Kubernetes, you can expose the pod IP [through an environment variable](https://kubernetes.io/docs/tasks/inject-data-application/environment-variable-expose-pod-information/) via the container definition such as:
+If you are using Kubernetes, you can expose the pod IP [through an environment variable](https://kubernetes.io/docs/tasks/inject-data-application/environment-variable-expose-pod-information/) via the container definition.
 
 ```bash
 env:
@@ -42,3 +42,57 @@ env:
     fieldRef:
       fieldPath: status.podIP
 ```
+
+1. Add the port 9094 to the Grafana deployment:
+
+```yaml
+ports:
+  - containerPort: 3000
+    name: http-grafana
+    protocol: TCP
+  - containerPort: 9094
+    name: grafana-alert
+    protocol: TCP
+```
+
+2. Add the environment variables to the Grafana deployment:
+
+```yaml
+env:
+  - name: POD_IP
+    valueFrom:
+      fieldRef:
+        fieldPath: status.podIP
+```
+
+3. Create a headless service that returns the pod IP instead of the service IP, which is what the `ha_peers` need:
+
+```yaml
+apiVersion: v1
+kind: Service
+metadata:
+  name: grafana-alerting
+  namespace: grafana
+  labels:
+    app.kubernetes.io/name: grafana-alerting
+    app.kubernetes.io/part-of: grafana
+spec:
+  type: ClusterIP
+  clusterIP: 'None'
+  ports:
+    - port: 9094
+  selector:
+    app: grafana
+```
+
+4. Make sure your grafana deployment has the label matching the selector, e.g. `app:grafana`.
+
+5. Add in the grafana.ini:
+
+```bash
+[unified_alerting]
+enabled = true
+ha_listen_address = "${POD_IP}:9094"
+ha_peers = "grafana-alerting.grafana:9094"
+ha_advertise_address = "${POD_IP}:9094"
+```