![]() A cordoned node can continue to host the pods it is already running, but it cannot accept any new pods, even if it would normally satisfy all other scheduling predicates. If you cordon a node (e.g., to prepare the node for an upgrade), Kubernetes will mark it unschedulable. Nodes’ taints conflict with pods’ tolerations.Node labels conflict with pods’ node selectors or affinity rules.In this section, we’ll walk through some reasons why nodes can fail to meet these requirements and are thereby deemed ineligible to host Pending pods: Several predicates are designed to check that nodes meet certain requirements before allowing Pending pods to get scheduled on them. Some examples use jq to parse kubectl output if you are interested in following along, make sure you’ve installed it before proceeding. Next, we will examine how some of these predicates can lead to scheduling failures. If the scheduler cannot find any eligible nodes after checking these predicates, the pod will remain Pending until a suitable node becomes available. For efficiency, the scheduler evaluates predicates in a specific order, saving more complex decisions for the end. Kubernetes control plane, uses predicates to determine which nodes are eligible to host a Pending pod. While FailedScheduling events provide a general sense of what went wrong, having a deeper understanding of how Kubernetes makes scheduling decisions can be helpful in determining why Pending pods are not able to get scheduled. You can use this field to filter pods by phase, as shown in the following kubectl command: Kubernetes API server could not communicate with the pod’s node.Ī pod advertises its phase in the status.phase field of a PodStatus object. Failed: One or more of the pod’s containers terminated with an error.Succeeded: All of the pod’s containers exited without errors.Running: The pod has been assigned to a node and has one or more running containers.Pending: The pod is waiting to get scheduled on a node, or for at least one of its containers to initialize.Pods can be in any of the following phases: A primer on Kubernetes pod statusīefore proceeding, let’s take a brief look at how pod status updates work in Kubernetes. ![]()
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