Pod priority and preemption in Kubernetes - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the priority class name for a pod.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: example-pod
spec:
  priorityClassName: [1]
  containers:
  - name: nginx
    image: nginx

Drag options to blanks, or click blank then click option'

Ahigh-priority

Blow-priority

Cmedium-priority

Dno-priority

Attempts:

3 left

💡 Hint

Common Mistakes

Using a priority class name that does not exist in the cluster.

The priorityClassName field assigns the pod's priority. "medium-priority" is a common default priority class.

2fill in blank

medium

Complete the command to create a priority class with high priority.

Kubernetes

kubectl create priorityclass [1] --value=1000 --description="High priority class"

Drag options to blanks, or click blank then click option'

Amedium-priority

Blow-priority

Cdefault-priority

Dhigh-priority

Attempts:

3 left

💡 Hint

Common Mistakes

Using a priority class name that does not match the value.

The command creates a priority class named "high-priority" with a high value of 1000.

3fill in blank

hard

Fix the error in the pod spec to enable preemption by setting the correct field.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: preemptible-pod
spec:
  priorityClassName: high-priority
  [1]: "PreemptLowerPriority"
  containers:
  - name: busybox
    image: busybox
    command: ["sleep", "3600"]

Drag options to blanks, or click blank then click option'

AenablePreemption

BpreemptionPolicy

Cpreemptible

DallowPreemption

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent fields like 'enablePreemption' or 'allowPreemption'.

The correct field to control preemption behavior is preemptionPolicy. Setting it to "PreemptLowerPriority" enables preemption.

4fill in blank

hard

Fill both blanks to create a priority class YAML with correct apiVersion and kind.

Kubernetes

apiVersion: [1]
kind: [2]
metadata:
  name: custom-priority
value: 500
globalDefault: false
description: "Custom priority class"

Drag options to blanks, or click blank then click option'

Ascheduling.k8s.io/v1

Bv1

CPriorityClass

DPodPriority

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'v1' as apiVersion or 'PodPriority' as kind.

The apiVersion for priority classes is 'scheduling.k8s.io/v1' and the kind is 'PriorityClass'.

5fill in blank

hard

Fill in the blanks to write a pod spec that uses a priority class and disables preemption.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: no-preempt-pod
spec:
  priorityClassName: [1]
  preemptionPolicy: [2]
  containers:
  - name: app
    image: nginx
    command: ["nginx", "-g", "daemon off;"]

Drag options to blanks, or click blank then click option'

Ahigh-priority

BNever

Creplicas

Dpriority

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'replicas' in pod spec (only for deployments).

Setting preemptionPolicy to wrong values.

The pod uses the 'high-priority' class, sets preemptionPolicy to 'Never' to disable preemption.

Practice

1. What is the main purpose of pod priority in Kubernetes?

easy

A. To decide which pods get scheduled first when resources are limited

B. To assign network policies to pods

C. To control pod security settings

D. To manage pod storage volumes

Solution

1. Step 1: Understand pod priority concept

   Pod priority is used to rank pods by importance for scheduling decisions.

2. Step 2: Identify scheduling impact

   When resources are scarce, higher priority pods are scheduled before lower priority ones.

3. Final Answer:

   To decide which pods get scheduled first when resources are limited -> Option A

4. Quick Check:

   Pod priority controls scheduling order = A [OK]

Hint: Pod priority ranks pods for scheduling under resource limits [OK]

Common Mistakes:

• Confusing priority with security or network policies
• Thinking priority controls storage or volumes
• Assuming priority affects pod runtime behavior

2. Which YAML field correctly assigns a priority class to a pod?

easy

A. spec.priority: high-priority

B. metadata.priorityClass: high-priority

C. metadata.priorityClassName: high-priority

D. spec.priorityClassName: high-priority

Solution

1. Step 1: Recall pod spec fields

   The priority class is set under the pod's spec using priorityClassName.

2. Step 2: Verify correct YAML syntax

   Correct field is spec.priorityClassName, not metadata or spec.priority.

3. Final Answer:

   spec.priorityClassName: high-priority -> Option D

4. Quick Check:

   Priority class set in spec.priorityClassName = C [OK]

Hint: Use spec.priorityClassName to assign priority class in pod YAML [OK]

Common Mistakes:

• Placing priorityClassName under metadata instead of spec
• Using spec.priority instead of priorityClassName
• Misspelling the field name

3. Given these pods with priorities: Pod A (priority 1000), Pod B (priority 500), Pod C (priority 1000). If resources are limited and only two pods can run, which pods will Kubernetes schedule?

medium

A. Pod B and Pod C

B. Pod A and Pod C

C. Pod A and Pod B

D. Pod B only

Solution

1. Step 1: Compare pod priorities

   Pod A and Pod C have priority 1000, Pod B has 500.

2. Step 2: Select highest priority pods

   Kubernetes schedules pods with highest priority first, so Pod A and Pod C run.

3. Final Answer:

   Pod A and Pod C -> Option B

4. Quick Check:

   Highest priority pods scheduled = A [OK]

Hint: Schedule pods with highest priority first when resources are limited [OK]

Common Mistakes:

• Choosing pods with lower priority over higher
• Assuming all pods run regardless of resources
• Ignoring equal priority pods

4. You created a pod with priorityClassName: "high-priority" but it is not preempting lower priority pods when scheduled. What could be the reason?

medium

A. The priority class "high-priority" is not defined in the cluster

B. Pod preemption is disabled by default in Kubernetes

C. The pod spec is missing resource requests

D. The pod is running on a node with no other pods

Solution

1. Step 1: Check priority class existence

   If the priority class "high-priority" is not defined, the pod cannot use it for preemption.

2. Step 2: Understand preemption behavior

   Preemption requires a valid priority class; missing it disables preemption.

3. Final Answer:

   The priority class "high-priority" is not defined in the cluster -> Option A

4. Quick Check:

   Undefined priority class blocks preemption = D [OK]

Hint: Ensure priority class exists before expecting preemption [OK]

Common Mistakes:

• Assuming preemption is disabled by default
• Ignoring missing resource requests impact
• Not checking node pod status

5. You have a cluster with pods of different priorities. A new pod with priority 2000 is pending due to lack of resources. How does Kubernetes handle this situation?

hard

A. It waits until resources are manually freed without preemption

B. It schedules the new pod alongside others, causing resource overcommit

C. It preempts lower priority pods to free resources for the new pod

D. It deletes the new pod automatically due to insufficient resources

Solution

1. Step 1: Understand preemption role

   When a high priority pod is pending, Kubernetes can preempt lower priority pods to free resources.

2. Step 2: Apply preemption behavior

   Kubernetes stops lower priority pods to schedule the higher priority pod if possible.

3. Final Answer:

   It preempts lower priority pods to free resources for the new pod -> Option C

4. Quick Check:

   High priority pod triggers preemption = B [OK]

Hint: High priority pods preempt lower ones to get scheduled [OK]

Common Mistakes:

• Thinking Kubernetes waits without preemption
• Assuming resource overcommit happens automatically
• Believing new pods get deleted if pending