了解 percentOfNodesToScore 默认行为

Question

Kubernetes 调度程序在尝试调度 pod 时可能会使用集群节点的子集，具体取决于集群中的节点数量和调度程序Configuration。

我想知道默认行为是什么，因为kube-scheduler-config API 文档不清楚：

percentOfNodesToScore[必需] int32
PercentageOfNodesToScore 是一旦发现可运行 pod 的所有节点的百分比，调度程序将停止在集群中搜索更多可行节点。这有助于提高调度程序的性能。不管这个标志的值是什么，调度程序总是试图找到至少“minFeasibleNodesToFind”的可行节点。示例：如果集群大小为 500 个节点，并且该标志的值为 30，则调度程序一旦找到 150 个可行节点就停止寻找更多可行节点。当值为0时，默认的节点百分比（基于集群大小的5%--50%）将被计分。

Answer 1

kubernetes 1.25 中的调度程序默认行为在 KubeSchedulerConfiguration percentageOfNodesToScore 设置为 0 时启用。

默认行为是扫描 50% 的节点，该百分比通过集群中的节点数除以 125 来减少（例如：2500 个节点/125=20 => 50% - 20 点 => 扫描 30%节点）。要扫描的最小节点是总或 100 个节点的 5%。

要全面了解调度程序的行为，请深入了解 Kubernetes 源代码。函数numFeasibleNodesToFind（链接到kubernetes 1.25）

const (
    // SchedulerError is the reason recorded for events when an error occurs during scheduling a pod.
    SchedulerError = "SchedulerError"
    // Percentage of plugin metrics to be sampled.
    pluginMetricsSamplePercent = 10
    // minFeasibleNodesToFind is the minimum number of nodes that would be scored
    // in each scheduling cycle. This is a semi-arbitrary value to ensure that a
    // certain minimum of nodes are checked for feasibility. This in turn helps
    // ensure a minimum level of spreading.
    minFeasibleNodesToFind = 100
    // minFeasibleNodesPercentageToFind is the minimum percentage of nodes that
    // would be scored in each scheduling cycle. This is a semi-arbitrary value
    // to ensure that a certain minimum of nodes are checked for feasibility.
    // This in turn helps ensure a minimum level of spreading.
    minFeasibleNodesPercentageToFind = 5
)

// == trucated == //

// numFeasibleNodesToFind returns the number of feasible nodes that once found, the scheduler stops
// its search for more feasible nodes.
func (sched *Scheduler) numFeasibleNodesToFind(numAllNodes int32) (numNodes int32) {
    if numAllNodes < minFeasibleNodesToFind || sched.percentageOfNodesToScore >= 100 {
        return numAllNodes
    }

    adaptivePercentage := sched.percentageOfNodesToScore
    if adaptivePercentage <= 0 {
        basePercentageOfNodesToScore := int32(50)
        adaptivePercentage = basePercentageOfNodesToScore - numAllNodes/125
        if adaptivePercentage < minFeasibleNodesPercentageToFind {
            adaptivePercentage = minFeasibleNodesPercentageToFind
        }
    }

    numNodes = numAllNodes * adaptivePercentage / 100
    if numNodes < minFeasibleNodesToFind {
        return minFeasibleNodesToFind
    }

    return numNodes
}