Application Migration

Application migration from the cluster on a third-party cloud consists of two steps: application backup and application migration. That is, applications in the cluster on a third-party cloud are backed up and then migrated to the destination cluster through data restoration.

k8clone is a simple Kubernetes metadata cloning tool. It can save Kubernetes metadata (objects) as a local package and restore the metadata to the destination cluster (Huawei Cloud cluster or on-premises cluster of UCS). In this way, applications can be migrated from clusters in an on-premises data center to the cloud.

Constraints

Currently, applications in a cluster of a later version cannot be migrated to a cluster of an earlier version.

Prerequisites

Ensure that services (data not in the cluster, such as images, storage, and databases) on which cloud native applications depend have been migrated.
Ensure that the metadata backup in the source cluster has been downloaded to the server where k8clone is executed.

How k8clone Restores Data

Data restoration process:

Figure 1 Data restoration process

Before the restoration, prepare a data restoration configuration file restore.json to automatically change the storage class names of PVC and StatefulSet and the repository address of the image used by the workload during application restoration.

The file content is as follows:

{
    "StorageClass": 
          "OldStorageClassName": "NewStorageClassName"  // The StorageClassName field of PVC and StatefulSet can be changed.
    "ImageRepo": 
          "OldImageRepo1": "NewImageRepo1",   //eg:"dockerhub.com": "cn-north-4.swr.huaweicloud.com"
          "OldImageRepo2": "NewImageRepo2",   //eg:"dockerhub.com/org1": "cn-north-4.swr.huaweicloud.com/org2"
          "NoRepo": "NewImageRepo3"   //eg:"golang": "swr.cn-north-4.myhuaweicloud.com/paas/golang"
}

StorageClass: The storage class names of PVC and VolumeClaimTemplates can be automatically changed based on settings.
ImageRepo: The repository address of the image used by the workload can be changed. The workload can be Deployment (including initContainer), StatefulSet, Orphaned Pod, Job, CronJob, Replica Set, Replication Controller, and DaemonSet.

k8clone Usage for Restoration

k8clone can run on Linux (x86 and Arm) and Windows. The usage is similar in both environments. This section uses the Linux (x86) environment as an example.

If Linux (Arm) or Windows is used, replace k8clone-linux-amd64 in the following command with k8clone-linux-arm64 or k8clone-windows-amd64.exe.

Run ./k8clone-linux-amd64 restore -h in the directory where k8clone is located to learn about its usage.

-k, --kubeconfig: specifies the location of the kubeconfig file of kubectl. The default value is $HOME/.kube/config. The kubeconfig file is used to configure access to the Kubernetes cluster. The kubeconfig file contains the authentication credentials and endpoints (access addresses) required for accessing and registering the Kubernetes cluster. For details, see the Kubernetes documentation.
-s, --api-server: Kubernetes API Server URL. The default value is "".
-q, --context: Kubernetes Configuration Context. The default value is "".
-f, --restore-conf: path of restore.json. The default value is the directory where k8clone is located.
-d, --local-dir: path for storing backup data. The default value is the directory where k8clone is located.

$ ./k8clone-linux-amd64 restore -h
ProcessRestore from backup

Usage:
     k8clone restore [flags]

Flags:
   -s, --api-server string     Kubernetes api-server url
   -q, --context string        Kubernetes configuration context
   -h, --help                  help for restore
   -k, --kubeconfig string     The kubeconfig of k8s cluster's. Default is the $HOME/.kube/config. 
   -d, --local-dir string      Where to restore (default "./k8clone-dump.zip")
   -f, --restore-conf string   restore conf file (default "./restore.json")

Example:

./k8clone-linux-amd64 restore -d ./k8clone-dump.zip -f ./restore.json

Procedure

Connect to the destination cluster using kubectl. For details, see Connecting to a Cluster Using kubectl.
Prepare the data restoration configuration file restore.json.
Create a restore.json file, modify it based on the format, and place it in the directory where k8clone is located.

Example:
```
{
  "StorageClass": {
    "csi-disk": "csi-disk-new"
  },
  "ImageRepo": {
    "quay.io/coreos": "swr.cn-north-4.myhuaweicloud.com/paas"
  }
}
```
Go to the directory where k8clone is located and run the restoration command to restore the backup data to the destination cluster.
Example:

./k8clone-linux-amd64 restore -d ./k8clone-dump.zip -f ./restore.json