# Enforcing Pod Priority Classes

Pods can have priority. Priority indicates the importance of a Pod relative to other Pods. If a Pod cannot be scheduled, the scheduler tries to preempt (evict) lower priority Pods to make scheduling of the pending Pod possible. See [Kubernetes documentation](https://kubernetes.io/docs/concepts/scheduling-eviction/pod-priority-preemption/). 

In a multi-tenant cluster, not all users can be trusted, as a tenant owner could create Pods at the highest possible priorities, causing other Pods to be evicted/not get scheduled.

To prevent misuses of Pod Priority Class, Bill, the cluster admin, can enforce the allowed Pod Priority Class at tenant level:

```yaml
kubectl apply -f - << EOF
apiVersion: capsule.clastix.io/v1beta1
kind: Tenant
metadata:
  name: oil
spec:
  owners:
  - name: alice
    kind: User
  priorityClasses:
    allowed:
    - default
    allowedRegex: "^tier-.*$"
EOF
```

With the said Tenant specification, Alice can create a Pod resource if `spec.priorityClassName` equals to:

- `default`
- `tier-gold`, `tier-silver`, or `tier-bronze`, since these compile the allowed regex. 

If a Pod is going to use a non-allowed _Priority Class_, it will be rejected by the Validation Webhook enforcing it.

# What’s next

See how Bill, the cluster admin, can assign a pool of nodes to Alice's tenant. [Assign a nodes pool](./nodes-pool.md).