failed to find subsystem mount for required subsystem: pids
看起来 Failed to start ContainerManager failed to initialize top level QOS containers 是关键信息，但其实是 failed to find subsystem mount for required subsystem: pids。
现象
kubelet 启动失败，journalctl -u kubelet 发现报错，
kubelet.go:1380] Failed to start ContainerManager failed to initialize top level QOS containers: failed to update top level Burstable QOS cgroup : failed to set supported cgroup subsystems for cgroup [kubepods burstable]: failed to find subsystem mount for required subsystem: pids
分析
根据报错信息，定位到代码是在 setSupportedSubsystems 函数。
因此发现具体原因是 failed to find subsystem mount for required subsystem: pids 导致的，要看 cgroup [kubepods burstable]。
ls /sys/fs/cgroup/systemd/kubepods/burstable/ 发现并没有 pids 目录。
getSupportedSubsystems 函数是问题的关键点。
func getSupportedSubsystems() map[subsystem]bool {
supportedSubsystems := map[subsystem]bool{
&cgroupfs.MemoryGroup{}: true,
&cgroupfs.CpuGroup{}: true,
&cgroupfs.PidsGroup{}: false,
}
// not all hosts support hugetlb cgroup, and in the absent of hugetlb, we will fail silently by reporting no capacity.
supportedSubsystems[&cgroupfs.HugetlbGroup{}] = false
if utilfeature.DefaultFeatureGate.Enabled(kubefeatures.SupportPodPidsLimit) || utilfeature.DefaultFeatureGate.Enabled(kubefeatures.SupportNodePidsLimit) {
supportedSubsystems[&cgroupfs.PidsGroup{}] = true
}
return supportedSubsystems
}
同时看 kubelet 的 feature-gates，发现 SupportPodPidsLimit 在 kubelet 1.14 之后默认是开启的。 SupportNodePidsLimit 在 1.15 之后默认开启。
而我使用的是 kubelet 1.17 版本。
SupportPodPidsLimit: Enable the support to limiting PIDs in Pods.
解决方案
因此解决方案是把 SupportPodPidsLimit 和 SupportNodePidsLimit 禁用掉。编辑 kubelet.env 文件（具体路径得根据你的部署路径找），KUBELET_ARGS 增加一行 --feature-gates=SupportPodPidsLimit=false,SupportNodePidsLimit=false \。重启 kubelet，systemctl restart kubelet.service。
network plugin is not ready: cni config uninitialized
网络插件没安装好的情况下，kubelet 会报这个问题。