As containers continue to dominate modern application deployment models, many organizations still rely heavily on virtual machines (VMs) for legacy workloads, specialized environments, or complex system-level applications. Instead of choosing between the two, what if we could run both—VMs and containers—side by side within a single Kubernetes cluster?
That's exactly what KubeVirt enables.
What Is KubeVirt?
KubeVirt is an open-source project that extends Kubernetes to manage not only containers but also virtual machines. It treats VMs as first-class citizens in the Kubernetes ecosystem by abstracting VMs into custom resources and scheduling them using Kubernetes-native workflows.
Simply put: KubeVirt lets you run VMs like containers, but without sacrificing the advantages of virtualization.
Why Would You Run VMs in Kubernetes?
You might ask: “Isn’t Kubernetes meant for cloud-native, containerized apps?” Yes. But many enterprises face these challenges:
- Legacy workloads that can’t be containerized easily.
- Specialized software requiring full OS-level control.
- Gradual migration where some components are containerized, and others are not.
- Hybrid cloud strategies with mixed workloads.
- Dev/Test environments needing VM support alongside microservices.
How Does KubeVirt Work?
KubeVirt introduces a new CRD (Custom Resource Definition) called VirtualMachineInstance (VMI). When you define a VM using a YAML manifest, KubeVirt:
- Uses libvirt and QEMU to create the VM.
- Schedules it on a Kubernetes node using the usual scheduler.
- Runs the VM inside a container (usually inside a pod with special privileges).
- Exposes networking and storage through standard Kubernetes mechanisms (e.g., Services, PVCs).
Example: Spinning Up a VM Using KubeVirt
Here's a simple manifest to launch a VM inside Kubernetes:
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
name: ubuntu-vm
spec:
running: true
template:
metadata:
labels:
kubevirt.io/domain: ubuntu-vm
spec:
domain:
devices:
disks:
- disk:
bus: virtio
name: containerdisk
resources:
requests:
memory: 1Gi
volumes:
- name: containerdisk
containerDisk:
image: kubevirt/ubuntu-cloud-container-disk-demo
This creates a lightweight Ubuntu VM managed like any Kubernetes workload.
Benefits of Using KubeVirt
- Unified Platform: Manage both VMs and containers using the same tooling, policies, and CI/CD pipelines.
- Reduced Operational Overhead: No need to maintain separate systems like OpenStack or VMware for VMs.
- Kubernetes-native APIs: Developers interact with VMs just like any Kubernetes object (via kubectl).
- Elasticity: Leverage Kubernetes autoscaling and scheduling for VMs too.
- Enhanced Security and Multi-tenancy: Apply Kubernetes-native RBAC, NetworkPolicies, and isolation models to VMs.
- Dev/Test Use Cases: Great for developers needing full VMs for OS-level testing or legacy software.
Real-World Use Cases
| Use Case | Description |
|---|---|
| Legacy Modernization | Slowly migrate VMs to containers in the same platform. |
| Secure Sandboxing | Run apps in full OS environments for added isolation. |
| Dev/Test Labs | Launch VMs on demand for testing operating systems, agents, etc. |
| Mixed Workloads | Run microservices and monoliths side-by-side. |
| Edge Computing | Use lightweight Kubernetes nodes to host both VMs and containers at the edge. |
Challenges & Considerations
- Performance Overhead: VMs don’t have the same lightweight performance as containers.
- Security Boundaries: Running VMs inside pods introduces complexity in isolation.
- Persistent Storage: Proper planning required for VM disks and stateful workloads.
- Networking: Integrating VMs with container networking (CNI plugins) requires some setup.
Hey, if you have read thus far.
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