Troubleshooting Kubernetes Pods Stuck in Pending State

Introduction

If you run workloads on Kubernetes, encountering Pods stuck in the Pending state is a common challenge. This typically means the Pod couldn’t be scheduled on any node due to resource limitations or configuration issues. Understanding the Pod lifecycle, from creation to scheduling, is crucial for identifying the root cause.

In this blog, we will explore why Pods get stuck in Pending and walk through effective troubleshooting steps to resolve the issue.

Key Causes of Pods Stuck in the Pending State

Several factors can prevent a Pod from being scheduled, causing it to remain Pending:

Insufficient Resources (CPU/Memory):

One of the most frequent reasons a Pod stays in Pending is that the cluster simply doesn’t have enough free CPU or memory to meet the Pod’s requested resources. Even if nodes are available, the scheduler cannot place the Pod if none can fulfil the defined requests. This is often seen in clusters under heavy load or when Pods request more resources than what’s available.

Taints and Tolerations:

Kubernetes nodes can be tainted to prevent certain Pods from being scheduled on them unless the Pods explicitly tolerate those taints. If no node has the appropriate tolerations that match the taints on available nodes, the Pod cannot be scheduled and remains in the Pending state. This mechanism is often used to reserve specific nodes for critical workloads.

Node Selectors and Affinity Rules:

Kubernetes allows you to control Pod placement using node selectors, node affinity, and pod affinity/anti-affinity rules. These features help ensure Pods are deployed to specific nodes or alongside (or away from) other Pods. However, if the conditions defined in these rules cannot be satisfied by any node in the cluster, the Pod won’t be scheduled and will remain in the Pending state.

Persistent Volume Claims (PVCs):

If a Pod relies on a Persistent Volume Claim (PVC) and that volume is not yet bound or available, Kubernetes will hold off scheduling the Pod. This can happen if there are no suitable storage classes, dynamic provisioning fails, or the required volume doesn’t exist. The Pod stays Pending until the PVC is successfully bound.

Image Pull Issues:

A Pod can remain in the Pending state if Kubernetes encounters problems while pulling the specified container image. These issues often arise due to an incorrect image name or tag, missing credentials for accessing a private container registry, or network-related problems preventing access to the image source. While such cases usually result in events like ImagePullBackOff or ErrImagePull, the Pod initially stays in Pending until the image can be successfully fetched and pulled onto the node.

Init Containers Not Completing:

If your Pod configuration includes Init Containers, Kubernetes waits for them to complete before moving to the main container. If any Init Container fails, gets stuck, or restarts continuously, the Pod will remain in the Pending state. It won’t proceed to start the application containers until all Init Containers complete successfully.

Unmet Dependencies:

Before starting the Pod, Kubernetes checks for dependencies on other components, such as ConfigMaps, Secrets, Services, or custom resources. If any of these are missing or unavailable, the Kubelet will delay the Pod’s startup. The Pod will remain in the Pending state until all its dependencies are resolved.

How to Troubleshoot – Step-by-Step Guide

When a Pod is stuck in the Pending state, the key to resolving the issue is systematically checking cluster components and understanding scheduling behaviour.

• Check Pod Status and Node Assignment: Start by retrieving the Pod’s current status and node assignment details. This helps confirm whether the Pod has been scheduled or not. If no node name is listed, the scheduler hasn’t placed it yet.

• Describe the Pod for Scheduling Events: This command gives you a detailed view of the Pod’s configuration and current status, including events related to scheduling failures. Look for messages under the Events section, they often provide clues, such as insufficient CPU/memory, missing volumes, taint conflicts, or unsatisfied affinity rules.

• Check Cluster Events Chronologically: Sorting events by timestamp helps you identify what happened just before or after the Pod was scheduled (or attempted to be). This is useful for seeing PVC provisioning failures, image pull errors, or resource pressure alerts.

• Inspect Available Nodes: Check the list of available nodes in the cluster and their status. Ensure the nodes are Ready and capable of accepting new workloads.

• Describe a Specific Node: Describing a node gives detailed insights into its condition, including available resources, taints, and pressure warnings. This helps determine whether the node can host the Pod or why scheduling fails.

• Check PVC and Storage Status: Check PVC and Storage Status: If your Pod uses Persistent Volumes, verify that the associated PVCs are in the Bound state using kubectl get pvc. A PVC stuck in Pending indicates that Kubernetes cannot find or provision the required storage, which prevents the Pod from being scheduled.

If you’re running on an Amazon EKS cluster, ensure that the Amazon EBS CSI driver is installed and that the EBS-related pods in the kube-system namespace are running. If these pods are also stuck in Pending, check whether the nodes have appropriate tolerations configured. Missing or mismatched tolerations can prevent EBS driver pods from scheduling, which blocks PVC provisioning.

Useful Tool for Troubleshooting

While kubectl remains the go-to CLI tool for interacting with Kubernetes, visual or interactive tools can significantly improve the troubleshooting experience. Below is the suggested tool that can simplify and accelerate your debugging process:

Lens – The Kubernetes IDE

Lens is a powerful, user-friendly desktop application with a full-fledged Kubernetes dashboard. It provides a graphical interface to explore your cluster, making it easier to visualize:

• Pod statuses, events, and logs
• Node conditions and resource utilization
• Persistent Volume Claims (PVCs), ConfigMaps, Secrets, and Services
• Real-time insights into namespaces, workloads, and deployments

Lens also supports multiple clusters, RBAC access control, and terminal integration to run kubectl commands directly from the UI. It’s ideal for developers and DevOps engineers who want an efficient visual approach without writing repetitive CLI commands.

Conclusion

Troubleshooting a Kubernetes Pod stuck in the Pending state requires a clear understanding of how scheduling works and where it can fail.

Following a structured approach and using tools like kubectl and Lens, you can quickly identify and resolve the issue, ensuring your workloads are deployed smoothly and efficiently.

Drop a query if you have any questions regarding Kubernetes Pod and we will get back to you quickly.

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