kubelet启动方式分析

我们一般以systemd系统守护进程的方式启动kubelet

$ systemctl status kubelet
● kubelet.service - kubelet: The Kubernetes Node Agent
   Loaded: loaded (/etc/systemd/system/kubelet.service; enabled; vendor preset: disabled)
  Drop-In: /etc/systemd/system/kubelet.service.d
           └─10-kubeadm.conf
   Active: active (running) since Sat 2021-11-06 16:05:42 CST; 4 days ago
     Docs: http://kubernetes.io/docs/
  Process: 2153 ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/hugetlb/system.slice/kubelet.service (code=exited, status=0/SUCCESS)
  Process: 2150 ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/systemd/system.slice/kubelet.service (code=exited, status=0/SUCCESS)
  Process: 2143 ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/memory/system.slice/kubelet.service (code=exited, status=0/SUCCESS)
  Process: 2111 ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/cpuset/system.slice/kubelet.service (code=exited, status=0/SUCCESS)
  Process: 2105 ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/cpuacct/system.slice/kubelet.service (code=exited, status=0/SUCCESS)
  Process: 2061 ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/cpu/system.slice/kubelet.service (code=exited, status=0/SUCCESS)
 Main PID: 2168 (kubelet)
    Tasks: 230
   Memory: 867.4M
   CGroup: /system.slice/kubelet.service
           └─2168 /usr/local/bin/kubelet --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.co...

Nov 11 10:20:57 node1 kubelet[2168]: W1111 10:20:57.208900    2168 volume_linux.go:49] Setting volume ownership for /var/lib/kubelet/pods/5a15...
Nov 11 10:20:57 node1 kubelet[2168]: W1111 10:20:57.210533    2168 volume_linux.go:49] Setting volume ownership for /var/lib/kubelet/pods/5a15...
Nov 11 10:20:57 node1 kubelet[2168]: W1111 10:20:57.210833    2168 volume_linux.go:49] Setting volume ownership for /var/lib/kubelet/pods/5a15...
Nov 11 10:20:57 node1 kubelet[2168]: E1111 10:20:57.767389    2168 summary_sys_containers.go:47] Failed to get system container stats for "/sy...
Nov 11 10:20:58 node1 kubelet[2168]: I1111 10:20:58.064091    2168 topology_manager.go:219] [topologymanager] RemoveContainer - Contai...8291c7ef
Nov 11 10:20:58 node1 kubelet[2168]: I1111 10:20:58.064592    2168 topology_manager.go:219] [topologymanager] RemoveContainer - Contai...78e11ac7
Nov 11 10:20:58 node1 kubelet[2168]: E1111 10:20:58.074045    2168 pod_workers.go:191] Error syncing pod 2f3115c0-22d2-4094-a467-f543cd34da3f ...
Nov 11 10:20:58 node1 kubelet[2168]: E1111 10:20:58.082305    2168 pod_workers.go:191] Error syncing pod ea9d254d-3d05-4b69-b1ff-c986454078d8 ...
Nov 11 10:20:58 node1 kubelet[2168]: E1111 10:20:58.085689    2168 kuberuntime_manager.go:801] container start failed: CreateContainer...ot found
Nov 11 10:20:58 node1 kubelet[2168]: E1111 10:20:58.085713    2168 pod_workers.go:191] Error syncing pod ececebcf-daeb-45e1-8516-06a95d706293 ...
Hint: Some lines were ellipsized, use -l to show in full.

我们看下service配置

$ cat /etc/systemd/system/kubelet.service
[Unit]
Description=kubelet: The Kubernetes Node Agent
Documentation=http://kubernetes.io/docs/

[Service]
ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/cpu/system.slice/kubelet.service
ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/cpuacct/system.slice/kubelet.service
ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/cpuset/system.slice/kubelet.service
ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/memory/system.slice/kubelet.service
ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/systemd/system.slice/kubelet.service
ExecStartPre=/usr/bin/mkdir -p /sys/fs/cgroup/hugetlb/system.slice/kubelet.service
ExecStart=/usr/local/bin/kubelet
Restart=always
StartLimitInterval=0
RestartSec=10

[Install]
WantedBy=multi-user.target

其中启动部分执行了/usr/local/bin/kubelet二进制文件，启动的参数我们暂且不关注。

/usr/local/bin/kubelet二进制文件是由kubernetes源码编译而来，接下来让我们从kubelet源码角度分析它的启动流程