CKAD — QoS Classes

QoS Classes

Kubernetes assigns a Quality of Service class to each Pod based on its resource configuration. This affects eviction priority when a node runs low on resources.

QoS Class	Condition	Eviction Priority
Guaranteed	All containers have equal requests and limits for both CPU and memory	Lowest (last to be evicted)
Burstable	At least one container has requests or limits set, but not equal	Medium
BestEffort	No requests or limits set on any container	Highest (first to be evicted)

Guaranteed Example

resources:
  requests:
    cpu: 500m
    memory: 256Mi
  limits:
    cpu: 500m      # Same as request
    memory: 256Mi   # Same as request

Burstable Example

resources:
  requests:
    cpu: 250m
    memory: 128Mi
  limits:
    cpu: 500m      # Different from request
    memory: 256Mi   # Different from request

BestEffort Example

# No resources section at all
containers:
- name: app
  image: nginx:1.27
  # No resources specified

# Check a Pod's QoS class
kubectl get pod app -o jsonpath='{.status.qosClass}'

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