Access to KubeVirt resources are controlled entirely by Kubernete’s Resource Based Access Control (RBAC) system. This system allows KubeVirt to tie directly into the existing authentication and authorization mechanisms Kubernetes already provides to its core api objects.
KubeVirt RBAC Role Basics
Typically, when people think of Kubernetes RBAC system, they’re thinking about granting users access to create/delete kubernetes objects (like Pods, deployments, etc), however those same RBAC mechanisms work naturally with KubeVirt objects as well.
When we look at KubeVirt’s objects, we can see they are structured just like the objects that come predefined in the Kubernetes core.
For example, look here’s an example of a VirtualMachine spec.
apiVersion: kubevirt.io/v1alpha1 kind: VirtualMachine metadata: name: vm-ephemeral spec: domain: devices: disks: - disk: bus: virtio name: registrydisk volumeName: registryvolume resources: requests: memory: 64M volumes: - name: registryvolume registryDisk: image: kubevirt/cirros-registry-disk-demo:devel
In the spec above, we see the KubeVirt VirtualMachine object has an apiVersion field and a kind field just like a Pod spec does. The kubevirt.io portion of the apiVersion field represents KubeVirt apiGroup the resource is a part of. The kind field reflects the resource type.
Using that information, we can create an RBAC role that gives a user permission to create, delete, and view all VirtualMachine objects.
apiVersion: rbac.authorization.k8s.io/v1beta1 kind: ClusterRole metadata: name: vm-access labels: kubevirt.io: "" rules: - apiGroups: - kubevirt.io resources: - virtualmachines verbs: - get - delete - create - update - patch - list - watch
This same logic can be applied when creating RBAC roles for other KubeVirt objects as well. If we wanted to extend this RBAC role to grant similar permissions for VirtualMachinePreset objects, we’d just have to add a second resource kubevirt.io resource list. The result would look like this.
apiVersion: rbac.authorization.k8s.io/v1beta1 kind: ClusterRole metadata: name: vm-access labels: kubevirt.io: "" rules: - apiGroups: - kubevirt.io resources: - virtualmachines - virtualmachinepresets verbs: - get - delete - create - update - patch - list - watch
KubeVirt Subresource RBAC Roles
Access to a VirtualMachines’s VNC and console stream using KubeVirt’s virtctl tool is managed by the Kubernetes RBAC system as well. Permissions for these resources work slightly different than the other KubeVirt objects though.
Console and VNC access is performed using the KubeVirt Stream API, which has its own api group called subresources.kubevirt.io. Below is an example of how to create a role that grants access to the VNC and console streams APIs.
apiVersion: rbac.authorization.k8s.io/v1beta1 kind: ClusterRole metadata: name: vm-vnc-access labels: kubevirt.io: "" rules: - apiGroups: - subresources.kubevirt.io resources: - virtualmachines/console - virtualmachines/vnc verbs: - get
Limiting RBAC To a Single Namespace.
A ClusterRole can be bound to a user in two different ways.
When a ClusterRoleBinding is used, a user is permitted access to all resources defined in the ClusterRole across all namespaces in the cluster.
When a RoleBinding is used, a user is limited to accessing only the resources defined in the ClusterRole within the namespace RoleBinding exists in.
Limiting RBAC To a Single Resource.
A user can also be limit to accessing only a single resource within a resource type. Below is an example that only grants VNC access to the VirtualMachine named ‘bobs-vm’
apiVersion: rbac.authorization.k8s.io/v1beta1 kind: ClusterRole metadata: name: vm-vnc-access labels: kubevirt.io: "" rules: - apiGroups: - subresources.kubevirt.io resources: - virtualmachines/console - virtualmachines/vnc resourceName: - bobs-vm verbs: - get
Default KubeVirt RBAC Roles
The next release of KubeVirt is coming with three default ClusterRoles that admins can use to grant users access to KubeVirt resources. In most cases, these roles will prevent admins from ever having to create their own custom KubeVirt RBAC roles.
More information about these default roles can be found in the KubeVirt user guide here