doc: add document for argocd

Signed-off-by: Yang Chiu <yang.chiu@suse.com>

content/docs/1.6.0/deploy/install/_index.md

@@ -13,6 +13,7 @@ Longhorn can be installed on a Kubernetes cluster in several ways:
 - [kubectl](./install-with-kubectl/)
 - [Helm](./install-with-helm/)
 - [Fleet](./install-with-fleet/)
+- [ArgoCD](./install-with-argocd/)
 
 To install Longhorn in an air gapped environment, refer to [this section.](../../advanced-resources/deploy/airgap)
 

content/docs/1.6.0/deploy/install/install-with-argocd.md

@@ -0,0 +1,98 @@
+---
+title: Install with ArgoCD
+weight: 12
+---
+
+## Prerequisites
+- Your workstation: Install the [Argo CD CLI](https://argo-cd.readthedocs.io/en/stable/cli_installation/).
+- Kubernetes cluster:
+  - Ensure that each node fulfills the [installation requirements](../#installation-requirements).
+  - Install [Argo CD](https://argo-cd.readthedocs.io/en/stable/).
+
+    ```bash
+    kubectl create namespace argocd
+    kubectl apply -n argocd -f https://raw.githubusercontent.com/argoproj/argo-cd/stable/manifests/core-install.yaml
+    ```
+    Allow some time for the deployment of Argo CD components in the `argocd` namespace.
+
+> Use [this script](https://github.com/longhorn/longhorn/blob/v{{< current-version >}}/scripts/environment_check.sh) to check the Longhorn environment for potential issues.
+
+## Installing Longhorn
+
+1. Log in to Argo CD.
+
+    ```bash
+    argocd login --core
+    ```
+
+1. Set the current namespace to `argocd`.
+
+    ```bash
+    kubectl config set-context --current --namespace=argocd
+    ```
+
+3. Create the Longhorn Application custom resource.
+
+    ```bash
+    cat > longhorn-application.yaml <<EOF
+    apiVersion: argoproj.io/v1alpha1
+    kind: Application
+    metadata:
+      name: longhorn
+      namespace: argocd
+    spec:
+      project: default
+      sources:
+        - chart: longhorn
+          repoURL: https://charts.longhorn.io/
+          targetRevision: v1.6.0 # Replace with the Longhorn version you'd like to install or upgrade to
+          helm:
+            values: |
+              helmPreUpgradeCheckerJob:
+                enabled: false
+      destination:
+        server: https://kubernetes.default.svc
+        namespace: longhorn-system
+    EOF
+    kubectl apply -f longhorn-application.yaml
+    ```
+
+1. Deploy Longhorn with the configured settings.
+
+    ```bash
+    argocd app sync longhorn
+    ```
+
+1. Verify that Longhorn was installed successfully.
+
+    ```bash
+    kubectl -n longhorn-system get pod
+    ```
+
+    Example of a successful Longhorn installation:
+
+    ```bash
+    NAME                                                READY   STATUS    RESTARTS   AGE
+    longhorn-ui-b7c844b49-w25g5                         1/1     Running   0          2m41s
+    longhorn-manager-pzgsp                              1/1     Running   0          2m41s
+    longhorn-driver-deployer-6bd59c9f76-lqczw           1/1     Running   0          2m41s
+    longhorn-csi-plugin-mbwqz                           2/2     Running   0          100s
+    csi-snapshotter-588457fcdf-22bqp                    1/1     Running   0          100s
+    csi-snapshotter-588457fcdf-2wd6g                    1/1     Running   0          100s
+    csi-provisioner-869bdc4b79-mzrwf                    1/1     Running   0          101s
+    csi-provisioner-869bdc4b79-klgfm                    1/1     Running   0          101s
+    csi-resizer-6d8cf5f99f-fd2ck                        1/1     Running   0          101s
+    csi-provisioner-869bdc4b79-j46rx                    1/1     Running   0          101s
+    csi-snapshotter-588457fcdf-bvjdt                    1/1     Running   0          100s
+    csi-resizer-6d8cf5f99f-68cw7                        1/1     Running   0          101s
+    csi-attacher-7bf4b7f996-df8v6                       1/1     Running   0          101s
+    csi-attacher-7bf4b7f996-g9cwc                       1/1     Running   0          101s
+    csi-attacher-7bf4b7f996-8l9sw                       1/1     Running   0          101s
+    csi-resizer-6d8cf5f99f-smdjw                        1/1     Running   0          101s
+    instance-manager-b34d5db1fe1e2d52bcfb308be3166cfc   1/1     Running   0          114s
+    engine-image-ei-df38d2e5-cv6nc                      1/1     Running   0          114s
+    ```
+
+1. [Create an NGINX Ingress controller with basic authentication](../../accessing-the-ui/longhorn-ingress) to access the Longhorn UI. Authentication to the Longhorn UI is not enabled by default.
+
+1. [Access the Longhorn UI](../../accessing-the-ui).