Pod stuck in Pending state in Kubernetes - Mini Project: Build & Apply

Troubleshooting a Pod Stuck in Pending State

📖 Scenario: You are managing a Kubernetes cluster for a small web application. One of your pods is stuck in the Pending state, which means it is not starting properly. You want to find out why and fix the issue so your application runs smoothly.

🎯 Goal: Learn how to check the pod status, understand why a pod might be stuck in Pending, and fix the problem by adjusting resource requests or node selectors.

📋 What You'll Learn

Use kubectl commands to check pod status

Inspect pod events to find the cause of Pending state

Modify pod configuration to fix resource or scheduling issues

Apply the fixed configuration and verify pod starts running

💡 Why This Matters

🌍 Real World

Pods stuck in Pending state are common when cluster resources are limited or pod specs are too demanding. Fixing these issues quickly keeps applications available.

💼 Career

DevOps engineers and Kubernetes administrators often troubleshoot pod scheduling problems to maintain healthy application deployments.

1

Check Pod Status

Use the command kubectl get pod myapp-pod to check the status of the pod named myapp-pod.

Kubernetes

# Run the command to check pod status
# Your code here

Hint

Use kubectl get pod followed by the pod name to see its current status.

2

Inspect Pod Events

Use the command kubectl describe pod myapp-pod to see detailed information and events for the pod myapp-pod. Look for messages explaining why it is Pending.

Kubernetes

kubectl get pod myapp-pod
# Run the command to describe the pod and check events
# Your code here

Hint

The kubectl describe pod command shows events like scheduling failures or resource shortages.

3

Fix Pod Resource Requests

Edit the pod configuration YAML to reduce the resources.requests.cpu value to 100m and resources.requests.memory to 128Mi. This helps if the pod is Pending due to insufficient resources.

Kubernetes

kubectl get pod myapp-pod
kubectl describe pod myapp-pod
# Edit the pod YAML to set cpu request to 100m and memory request to 128Mi
# Your code here

Hint

Open the pod YAML and find the resources.requests section. Change the CPU and memory values as instructed.

4

Apply Changes and Verify Pod Runs

Apply the updated pod configuration using kubectl apply -f pod.yaml. Then check the pod status again with kubectl get pod myapp-pod to confirm it is now Running.

Kubernetes

kubectl get pod myapp-pod
kubectl describe pod myapp-pod

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
spec:
  containers:
  - name: myapp-container
    image: nginx
    resources:
      requests:
        cpu: "100m"
        memory: "128Mi"

# Apply the pod.yaml file and check pod status
# Your code here

Hint

Use kubectl apply -f pod.yaml to update the pod, then kubectl get pod myapp-pod to see if it is Running.

Practice

1. What does it usually mean when a Kubernetes Pod is stuck in the Pending state?

easy

A. Kubernetes cannot find a suitable node to run the Pod.

B. The Pod has completed its task and is terminating.

C. The Pod is running but not responding to requests.

D. The Pod has been deleted from the cluster.

Solution

1. Step 1: Understand Pod lifecycle states

   The Pending state means the Pod is created but not yet scheduled to a node.

2. Step 2: Identify reason for Pending

   Pending usually happens when no node meets the Pod's resource or scheduling requirements.

3. Final Answer:

   Kubernetes cannot find a suitable node to run the Pod. -> Option A

4. Quick Check:

   Pending = No suitable node found [OK]

Hint: Pending means no node fits Pod's needs [OK]

Common Mistakes:

• Confusing Pending with Running state
• Thinking Pending means Pod is deleted
• Assuming Pending means Pod is ready

2. Which kubectl command helps you see detailed reasons why a Pod is stuck in Pending state?

easy

A. kubectl get pods

B. kubectl describe pod

C. kubectl logs

D. kubectl delete pod

Solution

1. Step 1: Identify command to get detailed Pod info

   kubectl describe pod shows events and status details for the Pod.

2. Step 2: Confirm command usage

   This command reveals scheduling failures or resource issues causing Pending.

3. Final Answer:

   kubectl describe pod <pod-name> -> Option B

4. Quick Check:

   Describe Pod = Detailed status [OK]

Hint: Use describe to see Pod events and reasons [OK]

Common Mistakes:

• Using get pods only shows summary, not reasons
• Using logs shows container logs, not scheduling info
• Deleting Pod does not show status

3. Given this kubectl describe pod mypod output snippet:

Events:
  Type     Reason            Age   From               Message
  ----     ------            ----  ----               -------
  Warning  FailedScheduling  2m    default-scheduler  0/3 nodes are available: 3 Insufficient cpu.

What is the main reason the Pod is stuck in Pending?

medium

A. There is no node with enough CPU available.

B. The Pod image is not found.

C. The Pod has a syntax error in its YAML.

D. The Pod is already running on another node.

Solution

1. Step 1: Analyze the event message

   The message says "0/3 nodes are available: 3 Insufficient cpu." meaning no node has enough CPU resources.

2. Step 2: Understand impact on scheduling

   Without enough CPU, the scheduler cannot place the Pod, so it stays Pending.

3. Final Answer:

   There is no node with enough CPU available. -> Option A

4. Quick Check:

   Insufficient CPU = Pod Pending [OK]

Hint: Look for 'Insufficient cpu' in describe events [OK]

Common Mistakes:

• Confusing image errors with scheduling errors
• Assuming YAML syntax causes Pending
• Thinking Pod runs on multiple nodes

4. You see a Pod stuck in Pending state. You check kubectl describe pod and find the message: 0/2 nodes are available: 2 node(s) didn't match Pod's node selector.
What should you do to fix this?

medium

A. Delete the Pod and recreate it without changes.

B. Increase the Pod's CPU requests to match node capacity.

C. Remove or correct the Pod's nodeSelector labels to match available nodes.

D. Restart the Kubernetes cluster.

Solution

1. Step 1: Understand nodeSelector impact

   The Pod's nodeSelector restricts scheduling to nodes with matching labels.

2. Step 2: Fix nodeSelector to match nodes

   Adjust or remove nodeSelector so nodes in cluster match Pod requirements.

3. Final Answer:

   Remove or correct the Pod's nodeSelector labels to match available nodes. -> Option C

4. Quick Check:

   nodeSelector mismatch = fix labels [OK]

Hint: Check and fix nodeSelector labels to match nodes [OK]

Common Mistakes:

• Increasing CPU requests worsens scheduling
• Deleting Pod without fixing selector won't help
• Restarting cluster is unnecessary

5. A Pod requests 4 CPUs but all nodes in your cluster have only 2 CPUs each. The Pod stays Pending. Which is the best way to fix this?

hard

A. Change the Pod's image to a smaller size.

B. Reduce the Pod's CPU request to 2 or less.

C. Remove resource requests from the Pod spec.

D. Add a node with at least 4 CPUs to the cluster.

Solution

1. Step 1: Understand resource requests vs node capacity

   The Pod requests 4 CPUs but nodes have only 2 CPUs, so no node can run it.

2. Step 2: Choose solution to meet resource needs

   Adding a node with enough CPUs allows the Pod to be scheduled properly.

3. Final Answer:

   Add a node with at least 4 CPUs to the cluster. -> Option D

4. Quick Check:

   Pod CPU request > node CPU = add bigger node [OK]

Hint: Match Pod CPU request with node CPU capacity [OK]

Common Mistakes:

• Reducing CPU request may not be possible or desired
• Removing requests can cause unstable scheduling
• Changing image size does not affect CPU requests