Priority classes

If a Pod on Kestrel sets priorityClassName, it must be one of the three allowlisted uber-user-* classes: uber-user-significant, uber-user-preempt-medium, or uber-user-preempt-high. Any other value — including the uber-infra-* classes reserved for platform workloads and the cluster-level uber-user-important class, which is not in the tenant allowlist — is rejected at admission. A Pod that omits priorityClassName is admitted at priority 0, below every class, so always set one explicitly. See Priority class allowlist for the Capsule enforcement details.

The three classes

Class	Value	Preemption policy	Can preempt others?	Can be preempted?
uber-user-preempt-high	2000	PreemptLowerPriority	Yes — any lower-priority Pod	Only by uber-infra-* (platform only)
uber-user-preempt-medium	1000	PreemptLowerPriority	Yes — significant-class Pods	By preempt-high and uber-infra-*
uber-user-significant	500	Never	No	By any preempt-* class and uber-infra-*

Higher value = higher scheduling priority. A Pod can only preempt Pods with a lower priority value — a lower-value Pod can never evict a higher-value one. The preempt-* classes use the PreemptLowerPriority policy, so when the cluster is short on resources they evict lower-priority Pods to make room. uber-user-significant uses the Never policy: it never evicts anyone and simply waits for capacity.

How preemption works

Preemption only kicks in when the cluster is full and a Pod cannot be scheduled:

• A uber-user-preempt-* Pod that cannot fit will evict lower-priority Pods to free capacity, lowest priority first.
• A uber-user-significant Pod (policy Never) never evicts anyone — when the cluster is full it sits Pending until capacity frees up.

Which class to use

uber-user-significant

Use for: workloads you can afford to lose — dev pods, scratch experiments, opportunistic batch jobs, and nightly CronJobs with weak SLAs.

Why: lowest user-tier priority. These pods are the first to be evicted when a preempt-* pod needs space. Non-preempting — they never evict anyone else. This is the right default for anything ephemeral or retry-tolerant.

The first-deployment walkthrough uses uber-user-significant because the demo workload is intentionally expendable.

uber-user-preempt-medium

Use for: deadline-bound batch jobs — research runs that need to complete now and are worth taking capacity from significant peers.

Why: preempts significant-class pods to make room. Does not preempt preempt-high. Use when you have a real deadline and are willing to displace opportunistic workloads.

uber-user-preempt-high

Use for: production long-running services and critical interactive workloads — Deployments backing tenant-facing Ingress routes (the /running/workloads/long-running-service recommended variant), live analysis sessions, or time-sensitive dev pods where downtime costs more than the blast radius.

Why: highest user-tier priority. Preempts everything below it in the user tier (preempt-medium and significant) to stay scheduled under cluster pressure. Use sparingly — this is the highest blast radius among the three classes. If everyone uses preempt-high, nobody benefits from preemption because peers cancel each other out.

What about uber-infra-*?

The uber-infra-* classes exist at values around 900,000,000 — effectively infinitely higher than any user class. They are reserved for RCS-operated platform workloads (monitoring agents, Capsule controllers, etc.). Tenants cannot use them; Capsule admission rejects the attempt.

User preempt-* pods cannot evict infra pods. They can only evict each other or significant-class user pods.

Quick-reference mapping

Workload shape	Recommended class	Why
Production Deployment (Ingress-backed)	uber-user-preempt-high	Highest user-tier priority — stays scheduled under pressure
Critical live analysis session	uber-user-preempt-high	Worth the blast radius — use sparingly
Deadline-bound research Job	uber-user-preempt-medium	Willing to preempt opportunistic peers
Dev pod / scratch experiment	uber-user-significant	Expendable, eviction-tolerant
Nightly CronJob (weak SLA)	uber-user-significant	Re-runs tomorrow if preempted