Kubernetes pod pending failures: How to debug

A Pending pod in Kubernetes is unable to get scheduled on any node because the scheduler cannot find a suitable node that meets its scheduling requirements. This can happen due to various reasons such as node-based scheduling constraints, pods' requested resources exceeding allocatable capacity, PersistentVolume-related issues, or rolling update deployment settings. To debug Pending pods, it's essential to understand how Kubernetes makes scheduling decisions and evaluate predicates in a specific order. Node-based scheduling constraints, including readiness and taints, are checked first, followed by pods' requested resources exceeding allocatable capacity, PersistentVolume-related issues, pod affinity or anti-affinity rules, and rolling update deployment settings. By analyzing the "Events" section of the `kubectl describe` output and looking at the "Tolerations" and "Events" sections, it's possible to identify why a Pending pod is not getting scheduled. Additionally, monitoring Kubernetes with tools like Datadog can help detect abnormal scheduling issues and provide visibility into critical problems. To troubleshoot Kubernetes Pending pods, it's recommended to start by checking node conditions, node labels, and taints, as well as evaluating rolling update deployment settings.

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