Priority classes for critical workloads in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a PriorityClass in Kubernetes?

A PriorityClass is a Kubernetes resource that defines the priority level for pods. It helps the system decide which pods to schedule or evict first when resources are limited.

intermediate

How does Kubernetes use PriorityClasses during resource contention?

Kubernetes schedules pods with higher priority classes before lower priority ones. If resources run out, it evicts lower priority pods first to make room for higher priority pods.

beginner

What is the significance of the 'value' field in a PriorityClass?

The 'value' field is a number that defines the priority level. Higher numbers mean higher priority. For example, a PriorityClass with value 1000 is more important than one with 500.

intermediate

Can you create a PriorityClass for a critical workload? What key fields must it include?

Yes. A PriorityClass must include: metadata.name (unique name), value (priority number), and optionally description and globalDefault (if it should be default).

beginner

What happens if a pod does not specify a PriorityClass?

If a pod does not specify a PriorityClass, it gets the default priority, which is usually zero or the globalDefault PriorityClass if set. It will be scheduled and evicted with lower priority compared to pods with higher PriorityClasses.

What does a higher 'value' in a PriorityClass mean?

A Higher priority for scheduling and eviction decisions

B Lower priority for scheduling

C No effect on pod scheduling

D Only affects pod labels

Higher 'value' means the pod is more important and gets scheduled first or evicted last.

Which pods are evicted first when the node runs out of resources?

A Pods with the lowest PriorityClass value

B Pods with the highest PriorityClass value

C Pods with the most CPU usage

D Pods created last

Pods with lower priority are evicted first to free resources for higher priority pods.

What is the purpose of the 'globalDefault' field in a PriorityClass?

A Makes the PriorityClass apply only to global pods

B Marks this PriorityClass as the default for pods without a specified priority

C Disables the PriorityClass

D Sets the priority to zero

'globalDefault: true' means pods without a PriorityClass get this priority by default.

How do you assign a PriorityClass to a pod?

A Use an annotation 'priority-class' on the pod

B Set a label 'priorityClass' on the pod

C Specify 'priorityClassName' in the pod spec

D PriorityClass is assigned automatically

Pods specify the PriorityClass by setting 'priorityClassName' in their spec.

What happens if two pods have the same PriorityClass value?

A Both pods are scheduled simultaneously always

B Pods with the same value are evicted immediately

C Pods with the same value cannot exist

D Kubernetes uses other factors like creation time to decide scheduling

If priorities are equal, Kubernetes uses other criteria like creation time or resource requests.

Explain how PriorityClasses help Kubernetes manage critical workloads during resource shortages.

Think about how Kubernetes decides which pods to keep or remove when resources are tight.

Describe the steps to create and use a PriorityClass for a critical workload pod.

Focus on resource creation and pod specification.