Priority classes for critical workloads in Kubernetes - Mini Project: Build & Apply

Priority classes for critical workloads

📖 Scenario: You are managing a Kubernetes cluster that runs multiple applications. Some applications are critical and must always get resources first when the cluster is busy. To do this, Kubernetes uses PriorityClass objects to assign priority levels to pods.In this project, you will create a priority class for critical workloads and assign it to a pod to ensure it gets scheduled before less important pods.

🎯 Goal: Create a PriorityClass named critical-priority with a high priority value. Then create a pod that uses this priority class. Finally, verify the pod's priority class is set correctly.

📋 What You'll Learn

Create a PriorityClass named critical-priority with value 1000000

Create a pod named critical-pod that uses the critical-priority class

Verify the pod's priority class name is critical-priority

💡 Why This Matters

🌍 Real World

In real Kubernetes clusters, priority classes help ensure that important applications get resources first, especially when the cluster is busy or under resource pressure.

💼 Career

Understanding and using PriorityClasses is essential for Kubernetes administrators and DevOps engineers to manage workload scheduling and maintain application reliability.

1

Create the PriorityClass YAML

Create a YAML manifest named critical-priority.yaml that defines a PriorityClass with the name critical-priority and a value of 1000000. Include a description: "Priority class for critical workloads".

Kubernetes

# Your YAML manifest here

Hint

Use kind: PriorityClass and set metadata.name to critical-priority. The value should be 1000000.

2

Create the Pod YAML with priorityClassName

Create a YAML manifest named critical-pod.yaml that defines a pod with the name critical-pod. Use the critical-priority PriorityClass by setting priorityClassName: critical-priority in the pod spec. Use the nginx image for the container.

Kubernetes

apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: critical-priority
value: 1000000
description: "Priority class for critical workloads"
globalDefault: false
preemptionPolicy: PreemptLowerPriority

# Your pod YAML manifest here

Hint

Set priorityClassName: critical-priority inside the pod spec. Use nginx as the container image.

3

Apply the manifests to the cluster

Run the commands to apply both critical-priority.yaml and critical-pod.yaml to your Kubernetes cluster using kubectl apply -f.

Kubernetes

apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: critical-priority
value: 1000000
description: "Priority class for critical workloads"
globalDefault: false
preemptionPolicy: PreemptLowerPriority
---
apiVersion: v1
kind: Pod
metadata:
  name: critical-pod
spec:
  priorityClassName: critical-priority
  containers:
  - name: nginx
    image: nginx

# Run kubectl apply commands below

Hint

Use kubectl apply -f critical-priority.yaml and kubectl apply -f critical-pod.yaml to apply the manifests.

4

Verify the pod's priority class

Run the command kubectl get pod critical-pod -o jsonpath='{.spec.priorityClassName}' to display the pod's priority class name. This should output critical-priority.

Kubernetes

apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: critical-priority
value: 1000000
description: "Priority class for critical workloads"
globalDefault: false
preemptionPolicy: PreemptLowerPriority
---
apiVersion: v1
kind: Pod
metadata:
  name: critical-pod
spec:
  priorityClassName: critical-priority
  containers:
  - name: nginx
    image: nginx

kubectl apply -f critical-priority.yaml
kubectl apply -f critical-pod.yaml

# Run the command to get the pod's priorityClassName

Hint

Use kubectl get pod critical-pod -o jsonpath='{.spec.priorityClassName}' to check the priority class name.

Practice

1. What does a higher value in a Kubernetes PriorityClass mean?

easy

A. The pod will be scheduled on nodes with more memory.

B. The pod will use less CPU resources.

C. The pod has a higher priority and is more important.

D. The pod will restart automatically on failure.

Solution

1. Step 1: Understand PriorityClass value meaning

   In Kubernetes, the value field in a PriorityClass defines the importance of the pod. Higher values mean higher priority.

2. Step 2: Relate priority to pod importance

   Pods with higher priority are considered more critical and get scheduled before lower priority pods.

3. Final Answer:

   The pod has a higher priority and is more important. -> Option C

4. Quick Check:

   Higher value = higher priority [OK]

Hint: Higher PriorityClass value means more important pod [OK]

Common Mistakes:

• Confusing priority with resource limits
• Thinking priority controls pod restart behavior
• Assuming priority affects node selection by memory

2. Which of the following is the correct YAML snippet to define a PriorityClass named high-priority with value 1000 and globalDefault: false?

easy

A. apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: high-priority
value: 1000
globalDefault: false
description: "High priority class"

B. apiVersion: v1
kind: PriorityClass
metadata:
name: high-priority
priority: 1000
default: false

C. apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: high-priority
value: 1000
globalDefault: true
description: "High priority class"

D. apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: high-priority
value: "1000"
globalDefault: false
description: "High priority class"

Solution

1. Step 1: Check correct apiVersion and kind

   The correct apiVersion for PriorityClass is scheduling.k8s.io/v1 and kind is PriorityClass.

2. Step 2: Verify fields and types

   The field for priority is value (integer), not priority. globalDefault is a boolean. The value must be an integer, not a string.

3. Final Answer:

   YAML with apiVersion scheduling.k8s.io/v1, kind PriorityClass, value 1000 as integer, globalDefault false -> Option A

4. Quick Check:

   Correct apiVersion and value field [OK]

Hint: Use 'value' as integer and correct apiVersion [OK]

Common Mistakes:

• Using wrong apiVersion or kind
• Using 'priority' instead of 'value'
• Setting value as string instead of integer

3. Given this PriorityClass YAML and pod spec, what priority value will the pod have?

apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: critical
value: 2000
globalDefault: false
description: "Critical priority"

---

apiVersion: v1
kind: Pod
metadata:
  name: test-pod
spec:
  priorityClassName: critical
  containers:
  - name: app
    image: nginx

medium

A. 1000

B. 2000

C. 0

D. Pod will fail to schedule

Solution

1. Step 1: Identify PriorityClass used by pod

   The pod specifies priorityClassName: critical, so it uses the PriorityClass named 'critical'.

2. Step 2: Find priority value of 'critical'

   The PriorityClass 'critical' has value: 2000, so the pod's priority is 2000.

3. Final Answer:

   2000 -> Option B

4. Quick Check:

   Pod priority matches PriorityClass value [OK]

Hint: Pod priority equals PriorityClass value it references [OK]

Common Mistakes:

• Assuming default priority 0 without PriorityClass
• Confusing priorityClassName with container image
• Thinking pod fails without globalDefault

4. You created a PriorityClass with globalDefault: true but pods without priorityClassName still have priority 0. What is the likely cause?

medium

A. The PriorityClass value is set to 0.

B. globalDefault only works for DaemonSets, not pods.

C. Pods must specify priorityClassName to get any priority.

D. The PriorityClass resource was not applied correctly.

Solution

1. Step 1: Understand globalDefault behavior

   A PriorityClass with globalDefault: true sets the default priority for pods without a specified class.

2. Step 2: Check why pods have priority 0

   If pods still have priority 0, likely the PriorityClass was not created or applied properly, so Kubernetes does not see it as default.

3. Final Answer:

   The PriorityClass resource was not applied correctly. -> Option D

4. Quick Check:

   globalDefault requires correct PriorityClass creation [OK]

Hint: Check if PriorityClass resource is applied when globalDefault fails [OK]

Common Mistakes:

• Assuming pods need priorityClassName despite globalDefault
• Setting globalDefault on PriorityClass with value 0
• Believing globalDefault only applies to DaemonSets

5. You want to ensure that all pods without a specified PriorityClass get a default priority of 500, but also have a critical class with priority 2000. Which YAML snippet correctly sets this up?

hard

A. apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: default-priority
value: 500
globalDefault: true
description: "Default priority"
---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: critical
value: 2000
globalDefault: false
description: "Critical priority"

B. apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: critical
value: 2000
globalDefault: true
description: "Critical priority"
---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: default-priority
value: 500
globalDefault: false
description: "Default priority"

C. apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: default-priority
value: 500
globalDefault: false
description: "Default priority"
---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: critical
value: 2000
globalDefault: true
description: "Critical priority"

D. apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: default-priority
value: 500
globalDefault: true
description: "Default priority"
---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
name: critical
value: 2000
globalDefault: true
description: "Critical priority"

Solution

1. Step 1: Identify globalDefault usage

   Only one PriorityClass can have globalDefault: true. This sets the default priority for pods without a class.

2. Step 2: Assign correct priorities

   Set the default-priority class with value 500 and globalDefault true. Set critical class with value 2000 and globalDefault false.

3. Final Answer:

   Default priority 500 with globalDefault true, critical 2000 without globalDefault -> Option A

4. Quick Check:

   Only one globalDefault PriorityClass allowed [OK]

Hint: Only one PriorityClass can have globalDefault true [OK]

Common Mistakes:

• Setting globalDefault true on multiple PriorityClasses
• Confusing which class should be default
• Using same priority value for default and critical