前言

centos7之后, 所有的service都推荐使用systemd/systemctl来管理.

systemctl使用方式

• 查看所有的service

# systemctl list-units --all

• 查看service的配置项

[root@davywalker-centos7 ~]# systemctl cat vncserver@\\\\:1.service
# /etc/systemd/system/vncserver@:1.service
# The vncserver service unit file

[davywalker@davywalker-centos7 ~]$ systemctl cat sshd.service
# /usr/lib/systemd/system/sshd.service
[Unit]
Description=OpenSSH server daemon
Documentation=man:sshd(8) man:sshd_config(5)
After=network.target sshd-keygen.service
Wants=sshd-keygen.service

systemctl开发方式

// TODO: 写一个程序, 以service方式配置

systemd控制资源

systemd除了可以控制服务的启动顺序外, 还可以控制各个服务的资源消耗. 底层也是通过cgroups来实现.

K8s针对Host资源的控制, 有如下 2 种实现方式: Container Runtimes | Kubernetes

1. 基于普通的cgroups
2. 基于systemd, 详细使用方式参见: Chapter 14. Using systemd to manage resources used by applications Red Hat Enterprise Linux 9 | Red Hat Customer Portal

具体选择哪种?

K8s choose cgroupfs or systemd? - SoByte

如果在systemd的版本里使用cgroups驱动, 那么会导致有 2 个cgroups manager, 一个是systemd天然的, 一个是kubelet里的, 在节点压力过大时, 会导致节点不稳定.

there are two managers coexisting in a system, it will end up with two views of those resources. Cases have been reported in this area where some nodes are configured so that kubelet and docker use cgroupfs while the rest of the processes running on the node use systemd; such nodes can become unstable under resource pressure.