How to use an ACK One Fleet instance to deploy an application across multiple clusters -

You can use a Distributed Cloud Container Platform for Kubernetes (ACK One) Fleet instance to deploy an application across multiple clusters that are associated with the Fleet instance. To use the preceding method, you need to create Kubernetes resources, such as Deployments, Services, and Ingresses, for the application. Then, you need to specify the clusters in which you want to deploy the application and create the application. You can view the deployment progress of the application in each cluster. This topic describes how to use an ACK One Fleet instance to deploy an application across multiple clusters.

Prerequisites

The Fleet management feature is enabled. For more information, see Enable Fleet management.
Multiple clusters are associated with the Fleet instance. For more information, see Associate clusters with a Fleet instance.
The kubeconfig file of the Fleet instance is obtained in the ACK One console and a kubectl client is connected to the Fleet instance.
The AMC command-line tool is installed. For more information, see Use AMC.

Creates an application.

Run the following command to create a namespace.
Replace <your-namespace> with the name of the namespace that you want to create.
```
kubectl create namespace <your-namespace>
```

Create a file named app-meta.yaml and add the following content to the file. The file defines the Kubernetes resources that are required for deploying an application.

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: demo
  name: demo
  namespace: demo
spec:
  replicas: 1
  selector:
    matchLabels:
      app: demo
  template:
    metadata:
      labels:
        app: demo
    spec:
      containers:
      - image: registry.cn-hangzhou.aliyuncs.com/acs/rollouts-demo:red
        name: demo
---
apiVersion: v1
kind: Secret
metadata:
  name: demo
  namespace: demo
  labels:
    app: demo
type: Opaque
data:
  version: MQ==
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: demo-1
  namespace: demo
  labels:
    app: demo
data:
  version: "1"
---
apiVersion: v1
kind: Service
metadata:
  name: demo
  namespace: demo
  labels:
    app: demo
spec:
  selector:
    app: demo
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: demo
  namespace: demo
  labels:
    app: demo
spec:
  rules:
    - host: app.demo.example.com
      http:
        paths:
        - path: /
          pathType: Prefix
          backend:
            service:
              name: demo
              port:
                number: 80

Run the following command to deploy an application named demo on the Fleet instance:
```
kubectl apply -f app-meta.yaml
```

Create a file named app.yaml and add the following content to the file. The file defines a KubeVela application named demo.

Run the following command to query the clusters that are associated with the Fleet instance:

kubectl get managedclusters

Expected output:

NAME                     HUB ACCEPTED   MANAGED CLUSTER URLS   JOINED   AVAILABLE   AGE
managedcluster-c5****    true                                  True     True        12d
managedcluster-c1****    true                                  True     True        12d

Replace <clusterid1> and <clusterid2> with the IDs of the clusters in which you want to deploy the application.

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: demo
  namespace: demo
  annotations:
    app.oam.dev/publishVersion: version1
spec:
  components:
    - name: demo
      type: ref-objects
      properties:
        objects:
          - apiVersion: apps/v1
            kind: Deployment
            name: demo
          - apiVersion: v1
            kind: ConfigMap
            selector:
              app: demo
          - apiVersion: v1
            kind: Secret
            name: demo
          - apiVersion: v1
            kind: Service
            name: demo
          - apiVersion: networking.k8s.io/v1
            kind: Ingress
            name: demo
  policies:
    - type: topology
      name: beijing-clusters
      properties:
        clusters: ["<clusterid1>", "<clusterid2>"]  # Specify the IDs of the clusters in which you want to deploy the application. You can add or remove cluster IDs on demand.

Parameter	Description
`annotations. app.oam.dev/publishVersion`	The version of the application. If an application or the Kubernetes resources that are used by an application are updated, you must change the value of this parameter to trigger the Fleet instance to synchronize the updates to the clusters.
`components. type: ref-objects`	The `apiVersion`, `kind`, and `name` parameters are used to reference Kubernetes resources in the same namespace. The Fleet instance deploys these resources in the specified clusters. ACK One supports the following Kubernetes resources: `Deployment/apps/v1`, `Secret/v1`, `ConfigMap/v1`, and `Ingress/networking.k8s.io/v1`. If you require other resources, submit a ticket to contact the ACK One team.
`policies. type: topology`	Set the type of the policy to topology. A topology policy specifies the destinations to which Kubernetes resources are deployed.
`policies. properties. clusters`	You can specify destinations only by cluster ID. Each destination can contain one or more clusters that are associated with the Fleet instance.

Run the following command to deploy the application demo on the Fleet instance:
```
kubectl apply -f app.yaml
```

Run the following command to query the deployment progress of the application:

kubectl get app demo -n demo

Expected output:

NAME   COMPONENT   TYPE          PHASE     HEALTHY   STATUS   AGE
demo   demo        ref-objects   running   true               24m

Query the deployment progress of the Kubernetes resources in each destination cluster.

kubectl get app demo -n demo -o yaml
......
status:
  appliedResources:
  - apiVersion: apps/v1
    cluster: <clusterid1>
    creator: workflow
    kind: Deployment
    name: demo
    namespace: demo
  - apiVersion: v1
    cluster: <clusterid1>
    creator: workflow
    kind: ConfigMap
    name: demo-1
    namespace: demo
  - apiVersion: v1
    cluster: <clusterid1>
    creator: workflow
    kind: Secret
    name: demo
    namespace: demo
  - apiVersion: networking.k8s.io/v1
    cluster: <clusterid1>
    creator: workflow
    kind: Ingress
    name: demo
    namespace: demo
  - apiVersion: apps/v1
    cluster: <clusterid2>
    creator: workflow
    kind: Deployment
    name: demo
    namespace: demo
  - apiVersion: v1
    cluster: <clusterid2>
    creator: workflow
    kind: ConfigMap
    name: demo-1
    namespace: demo
  - apiVersion: v1
    cluster: <clusterid2>
    creator: workflow
    kind: Secret
    name: demo
    namespace: demo
  - apiVersion: networking.k8s.io/v1
    cluster: <clusterid2>
    creator: workflow
    kind: Ingress
    name: demo
    namespace: demo

Run the following command to query the status of Kubernetes resources in the specified destination cluster:

Replace <clusterid1> with the ID of the destination cluster.

kubectl amc get deployment demo -n demo -m <clusterid1>

Expected output:

Run on ManagedCluster <clusterid1>
NAME   READY   UP-TO-DATE   AVAILABLE   AGE
demo   1/1     1            1           28m

kubectl amc get pod -n demo -m <clusterid1>

Expected output:

Run on ManagedCluster <clusterid1>
NAME                    READY   STATUS      RESTARTS   AGE
demo-7c96b5bffd-****   1/1     Running     0          30m

Update the Kubernetes resources that are used by an application

To update the Kubernetes resources that are used by an application, perform the following steps:

Run the kubectl apply command to modify the Kubernetes resources that are deployed in Step 2.
You can modify the Kubernetes resources based on your business requirements. For example, you can modify the OS image in a Deployment, the port of a Service, or the Secret in a ConfigMap. The updates are automatically synchronized to the destination clusters.
Run the kubectl apply command to modify the Kubernetes resources that are deployed for the application demo in Step 4. You must change the value of annotations: app.oam.dev/publishVersion: version1 to trigger the Fleet instance to deploy the updated Kubernetes resources in the destination clusters.
For example, you can change the value of app.oam.dev/publishVersion to version2.
Repeat Step 6, Step 7, and Step 8 to query the status of the application and resources.

Delete an application

Run the following command to delete an application. After you delete an application, the Kubernetes resources that are deployed in the destination clusters for the application are also deleted.

kubectl delete app demo -n demo