环境准备
cat <<EOF | sudo tee /etc/modules-load.d/containerd.conf
overlay
br_netfilter
EOF
sudo modprobe overlay
sudo modprobe br_netfilter
# 设置必需的 sysctl 参数，这些参数在重新启动后仍然存在。
cat <<EOF | sudo tee /etc/sysctl.d/99-kubernetes-cri.conf
net.bridge.bridge-nf-call-iptables = 1
net.ipv4.ip_forward = 1
net.bridge.bridge-nf-call-ip6tables = 1
EOF
# Apply sysctl params without reboot
sudo sysctl --system
安装containd
# 安装 containerd
## 设置仓库
### 安装所需包
sudo yum install -y yum-utils device-mapper-persistent-data lvm2
### 添加 Docker 仓库
sudo yum-config-manager \
--add-repo \
https://download.docker.com/linux/centos/docker-ce.repo
## 安装 containerd
sudo yum update -y && sudo yum install -y containerd.io
# 配置 containerd
sudo mkdir -p /etc/containerd
containerd config default | sudo tee /etc/containerd/config.toml
# 重启 containerd
sudo systemctl restart containerd
配置kubelet
#修改/usr/lib/systemd/system/kubelet.service
[Unit]
Description=Kubernetes Kubelet
Documentation=https://github.com/kubernetes/kubernetes
After=containerd.service
Requires=containerd.service
[Service]
ExecStart=/usr/local/bin/kubelet \
--container-runtime=remote --runtime-request-timeout=15m --container-runtime-endpoint=unix:///run/containerd/containerd.sock \
--bootstrap-kubeconfig=/etc/kubernetes/bootstrap.kubeconfig \
--kubeconfig=/etc/kubernetes/kubelet.kubeconfig \
--config=/etc/kubernetes/kubelet-conf.yml \
Restart=always
RestartSec=10s
[Install]
WantedBy=multi-user.target
重点是[Unit]中的After和Requires都要是containerd，并且kubelet的启动参数加上--container-runtime=remote --runtime-request-timeout=15m --container-runtime-endpoint=unix:///run/containerd/containerd.sock。
问题：
使用containerd作为CRI后，kubelet启动不成功，报错255，如下所示
systemctl状态.png
使用命令journalctl -xeu kubelet得到以下日志
journalctl日志.png
从上面可以知道kubelet启动失败的原因是连接不上containerd，但是检查发现containerd是正常运行的。
这种错误有可能是k8s版本与containerd的不匹配造成的，但是看网上其他人使用的版本与我的一致，并且正常运行，故可以排除这个可能。
最后发现是containerd的配置问题，因为我用yum安装containerd后忘了覆盖原有的配置，使得kubelet启动失败。解决方法就是删掉原来的配置文件，或者使用命令重新生成一份。
这里可以看下yum安装后的配置文件，根据查阅的资料显示，这里这么配的原因是因为docker需要用到。
# Copyright 2018-2020 Docker Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
disabled_plugins = ["cri"]
#root = "/var/lib/containerd"
#state = "/run/containerd"
#subreaper = true
#oom_score = 0
#[grpc]
# address = "/run/containerd/containerd.sock"
# uid = 0
# gid = 0
#[debug]
# address = "/run/containerd/debug.sock"
# uid = 0
# gid = 0
# level = "info"
关于该问题的其他讨论可以看这里.
