Live Migration

Live Migration is a common virtualization feature supported by KubeVirt where virtual machines running on one cluster node move to another cluster node without shutting down the guest OS or its applications.

To experiment with KubeVirt live migration in a Kubernetes test environment, some setup is required.

Start a Kubernetes cluster with the following requirements:

• Two or more nodes
• CNI plugin: Flannel is a good pick for proof on concept environments.
• Nested or emulated virtualization
• KubeVirt

For a simple test environment using Minikube, refer to the Minikube Quickstart on this site.

Check the status of nodes and kubevirt

To check on the nodes and their IP ranges run:

kubectl get nodes -o wide

This will return a report like

NAME           STATUS   ROLES                  AGE     VERSION   INTERNAL-IP      EXTERNAL-IP   OS-IMAGE               KERNEL-VERSION   CONTAINER-RUNTIME
minikube       Ready    control-plane,master   2m43s   v1.20.7   192.168.39.240   <none>        Buildroot 2020.02.12   4.19.182         docker://20.10.6
minikube-m02   Ready    <none>                 118s    v1.20.7   192.168.39.245   <none>        Buildroot 2020.02.12   4.19.182         docker://20.10.6

Check that kubevirt has fully deployed:

kubectl -n kubevirt get kubevirt
NAME       AGE     PHASE
kubevirt   3m20s   Deployed

Enable Live Migration

Live migration is, at the time of writing, not a standard feature in KubeVirt. To enable the feature, create a ConfigMap in the “kubevirt” Namespace called “kubevirt-config”.

kubectl apply -f - <<EOF
apiVersion: v1
kind: ConfigMap
metadata:
  name: kubevirt-config
  namespace: kubevirt
  labels:
    kubevirt.io: ""
data:
  feature-gates: "LiveMigration"
EOF

Create a Virtual Machine

Next, create a VM. This lab uses the “testvm” from lab1.

kubectl apply -f https://kubevirt.io/labs/manifests/vm.yaml
virtctl start testvm

In a multi-node environment, it is helpful to know on which node a pod is running. View its node using -o wide:

kubectl get pod -o wide

Notice in this example, the pod shows as running on NODE “minikube-m02”:

NAME                         READY   STATUS    RESTARTS   AGE   IP            NODE           NOMINATED NODE   READINESS GATES
virt-launcher-testvm-c8nzz   2/2     Running   0          32s   10.244.1.12   minikube-m02   <none>           <none>

Start a Service on the Virtual Machine

Using virtctl, expose two ports for testing, ssh and http/8080:

virtctl expose vmi testvm --name=testvm-ssh --port=22 --type=NodePort
virtctl expose vmi testvm --name=testvm-http --port=8080 --type=NodePort

Start by logging in to the console and running a simple web server using netcat:

virtctl console testvm

The default user “cirros” and its password are mentioned on the console login prompt, use them to log in. Next, run the following while loop to continuously respond to any http connection attempt with a test message:

while true; do ( echo "HTTP/1.0 200 Ok"; echo; echo "Migration test" ) | nc -l -p 8080; done

Leave the loop running, and either break out of the console with CTRL-] or open another terminal on the same machine.

To test the service, several bits of information will need to be coordinated. To collect the minikube node IP address and the NodePort of the http service, run:

IP=$(minikube ip)
PORT=$(kubectl get svc testvm-http -o jsonpath='{.spec.ports[0].nodePort}')

Now use curl to read data from the simple web service:

curl ${IP}:${PORT}

This should output Migration test. If all is well, it is time to migrate the virtual machine to another node.

Migrate VM

To migrate the testvm vmi from one node to the other, run:

virtctl migrate testvm

To ensure migration happens, watch the pods in “wide” view:

kubectl get pods -o wide

NAME                         READY   STATUS      RESTARTS   AGE    IP            NODE           NOMINATED NODE   READINESS GATES
virt-launcher-testvm-8src7   0/2     Completed   0          5m     10.244.1.14   minikube-m02   <none>           <none>
virt-launcher-testvm-zxlts   2/2     Running     0          21s    10.244.0.7    minikube       <none>           <none>

Notice the original virt-launcher pod has entered the Completed state and the virtual machine is now running on the minikube node. Test the service previously started is still running:

curl ${IP}:${PORT}

Again, this should output Migration test.

Summary

This lab is now concluded. This exercise has demonstrated the ability of KubeVirt Live Migration to move a running virtual machine from one node to another without requiring restart of running applications.