# 4. Running VMs in **Kubernetes**
crun-vm can also be used as a [Kubernetes] runtime, allowing you to run VMs as
regular pods.
Note that there is already a very featureful project, [KubeVirt], that enables
using Kubernetes to run VMs with great configurability. However, for simple use
cases, crun-vm may be a good fit.
Navigation
1. [Installing crun-vm](1-installing.md)
2. [Running VMs with **Podman** or **Docker**](2-podman-docker.md)
3. [Running VMs as **systemd** services](3-systemd.md)
4. **Running VMs in **Kubernetes****
- [**Setting up**](#setting-up)
- [**Creating VMs**](#creating-vms)
- [**Interacting with VMs**](#interacting-with-vms)
- [Exec'ing into VMs](#execing-into-vms)
- [Port forwarding](#port-forwarding)
- [**First-boot configuration**](#first-boot-configuration)
5. [**crun-vm(1)** man page](5-crun-vm.1.ronn)
## Setting up
You can use the [util/minikube-start.sh] script to set up a local [minikube]
Kubernetes cluster with crun-vm available as a runtime, and use it to easily try
out the examples below (note that this also points `kubectl` at the minikube
cluster):
```console
$ ./minikube-start.sh
Compiling crun-vm v0.2.0 (/home/afaria/crun-vm)
Finished dev [unoptimized + debuginfo] target(s) in 1.70s
😄 [crun-vm-example] minikube v1.32.0 on Fedora 40
[...]
🏄 Done! kubectl is now configured to use "crun-vm-example" cluster and "default" namespace by default
runtimeclass.node.k8s.io/crun-vm created
```
Once you're done, you can delete the cluster with:
```console
$ minikube -p crun-vm-example delete
```
To enable crun-vm on a real Kubernetes cluster, follow the instructions in [1.
Installing crun-vm].
## Creating VMs
To run a VM in your cluster, simply create a pod that references the
`RuntimeClass` corresponding to crun-vm (here we assume it is named `crun-vm`):
```yaml
apiVersion: v1
kind: Pod
metadata:
name: my-vm
spec:
containers:
- name: my-vm
image: quay.io/crun-vm/example-http-server:latest
ports:
- containerPort: 80
runtimeClassName: crun-vm
```
All the image formats supported by crun-vm when using Podman or Docker are also
supported here. See [2. Running VMs with **Podman** or
**Docker**](2-podman-docker.md#booting-vms) to know more.
You can inspect the VM's console output with the standard [`kubectl logs`]
command:
```console
$ kubectl logs my-vm
```
## Interacting with VMs
### Exec'ing into VMs
Assuming a VM supports cloud-init or Ignition, you can `ssh` into it using
`kubectl exec`:
```console
$ kubectl exec my-vm -- --as fedora whoami
fedora
$ kubectl exec -it my-vm -- --as fedora bash
[fedora@my-vm ~]$
```
The supported crun-vm specific options like `--as fedora` are the same as when
using crun-vm with Podman or Docker. See [2. Running VMs with **Podman** or
**Docker**](2-podman-docker.md#execing-into-vms) to know more.
### Port forwarding
The VM pod defined above actually exposes an HTTP server on port 80. To talk to
it, we must first forward a local port to the VM:
```console
$ kubectl port-forward my-vm 8000:80
Forwarding from 127.0.0.1:8000 -> 80
Forwarding from [::1]:8000 -> 80
```
With this command running, navigate to [`localhost:8000`] on your browser, or
run the following on a second terminal:
```console
$ curl localhost:8000
Directory listing for /
[...]
```
## First-boot configuration
Options supported when using crun-vm with Podman or Docker, like `--password`,
`--cloud-init`, and `--ignition`, are also supported here (see [2. Running VMs
with **Podman** or **Docker**](2-podman-docker.md#configuring-vms-on-first-boot)
for more information).
However, paths given to `--cloud-init` and `--ignition` are interpreted in the
context of the VM, instead of the host. This means that first-boot configuration
files can be retrieved from mounted volumes. For instance, you could store your
cloud-init configuration in a `ConfigMap`:
```yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: my-cloud-init-config
data:
meta-data: ""
user-data: |
#cloud-config
runcmd:
- echo 'Hello, world!' > /home/fedora/hello-world
```
And apply it to your VMs like so:
```yaml
apiVersion: v1
kind: Pod
metadata:
name: my-other-vm
spec:
containers:
- name: my-other-vm
image: quay.io/containerdisks/fedora:40
args:
- --cloud-init=/etc/cloud-init
volumeMounts:
- name: cloud-init-vol
mountPath: /etc/cloud-init
volumes:
- name: cloud-init-vol
configMap:
name: my-cloud-init-config
runtimeClassName: crun-vm
```
[`kubectl logs`]: https://kubernetes.io/docs/reference/kubectl/
[`localhost:8000`]: http://localhost:8000/
[1. Installing crun-vm]: 1-installing.md
[Kubernetes]: https://kubernetes.io/
[KubeVirt]: https://kubevirt.io/
[minikube]: https://minikube.sigs.k8s.io/
[util/minikube-start.sh]: ../util/minikube-start.sh