一.系统环境
| 服务器版本 | containerd软件版本 | CPU架构 |
|---|---|---|
| CentOS Linux release 7.4.1708 (Core) | 1.6.8 | x86_64 |
二.前言
在 Kubernetes 的早期，我们只支持一个容器运行时。那个运行时是 Docker 引擎。那时，并没有太多其他的选择，而 Docker 是处理容器的主要工具，所以这不是一个有争议的选择。最终，我们开始添加更多的容器运行时，比如 rkt 和 hypernetes，很明显 Kubernetes 用户希望选择最适合他们的运行时。因此，Kubernetes 需要一种方法来允许集群操作员灵活地使用他们选择的任何运行时。
发布了容器运行时接口(CRI) 以实现这种灵活性。CRI 的引入对项目和用户来说都很棒，但它确实引入了一个问题：Docker Engine 作为容器运行时的使用早于 CRI，并且 Docker Engine 不兼容 CRI。为了解决这个问题，引入了一个小型软件 shim (dockershim) 作为 kubelet 组件的一部分，专门用于填补 Docker Engine 和 CRI 之间的空白，允许集群操作员继续使用 Docker Engine 作为他们的容器运行时基本上不间断。
然而，这个小软件垫片从来没有打算成为一个永久的解决方案。多年来，它的存在给 kubelet 本身带来了许多不必要的复杂性。由于这个 shim，Docker 的一些集成实现不一致，导致维护人员的负担增加，并且维护供应商特定的代码不符合我们的开源理念。为了减少这种维护负担并朝着支持开放标准的更具协作性的社区迈进，引入了 KEP-2221，建议删除 dockershim。随着 Kubernetes v1.20 的发布，正式弃用。
自 Kubernetes v1.24 起，Dockershim 已被删除，这对项目来说是一个积极的举措。
自 Kubernetes v1.24 起，K8S默认使用containerd作为容器运行时！可以理解为containerd是docker的替代品。
好消息是containerd用法和docker类似，转型相当简单！
三.containerd
containerd 是一个行业标准的容器运行时，强调简单性、健壮性和可移植性。它可作为 Linux 和 Windows 的守护进程使用，可以管理其主机系统的完整容器生命周期：图像传输和存储、容器执行和监督、低级存储和网络附件等。containerd 旨在嵌入到更大的系统中，而不是由开发人员或最终用户直接使用。
containerd是从Docker中分离出来的一个项目，可以作为一个底层容器运行时，现在它成了Kubernete容器运行时更好的选择。docker 对容器的管理和操作基本都是通过 containerd 完成的
K8S发布CRI（Container Runtime Interface），统一了容器运行时接口，凡是支持CRI的容器运行时，皆可作为K8S的底层容器运行时。
如果你使用Docker作为K8S容器运行时的话，kubelet需要先要通过dockershim去调用Docker，再通过Docker去调用containerd。
如果你使用containerd作为K8S容器运行时的话，由于containerd内置了CRI插件，kubelet可以直接调用containerd。使用containerd不仅性能提高了（调用链变短了），而且资源占用也会变小（Docker不是一个纯粹的容器运行时，具有大量其他功能）。
四.部署containerd
4.1 安装containerd
安装containerd
[root@k8sworker2 ~]# yum -y install containerd.io cri-tools
已加载插件：fastestmirror
base | 3.6 kB 00:00:00
......
验证中 : containerd.io-1.4.12-3.1.el7.x86_64 4/4
更新完毕:
containerd.io.x86_64 0:1.6.8-3.1.el7 cri-tools.x86_64 0:1.24.2-0
完毕！
设置containerd开机自启动并启动containerd
[root@k8sworker2 ~]# systemctl enable containerd --now
Created symlink from /etc/systemd/system/multi-user.target.wants/containerd.service to /usr/lib/systemd/system/containerd.service.
[root@k8sworker2 ~]# systemctl status containerd
● containerd.service - containerd container runtime
Loaded: loaded (/usr/lib/systemd/system/containerd.service; enabled; vendor preset: disabled)
Active: active (running) since 四 2022-01-06 00:23:13 CST; 1min 4s ago
Docs: https://containerd.io
Main PID: 88228 (containerd)
CGroup: /system.slice/containerd.service
└─88228 /usr/bin/containerd
4.2 containerd配置文件
containerd的配置文件为/etc/containerd/config.toml
[root@k8sworker2 ~]# ll -h /etc/containerd/config.toml
-rw-r--r-- 1 root root 886 11月 18 04:15 /etc/containerd/config.toml
containerd的默认配置文件/etc/containerd/config.toml 内容如下
[root@k8sworker2 ~]# cat /etc/containerd/config.toml
# 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"
可以使用containerd config default > /etc/containerd/config.toml生成默认的配置文件，这个命令生成的配置文件内容很多
[root@k8sworker2 ~]# containerd config default
version = 2
root = "/var/lib/containerd"
state = "/run/containerd"
plugin_dir = ""
disabled_plugins = []
required_plugins = []
oom_score = 0
[grpc]
address = "/run/containerd/containerd.sock"
tcp_address = ""
tcp_tls_cert = ""
tcp_tls_key = ""
uid = 0
gid = 0
max_recv_message_size = 16777216
max_send_message_size = 16777216
[ttrpc]
address = ""
uid = 0
gid = 0
[debug]
address = ""
uid = 0
gid = 0
level = ""
[metrics]
address = ""
grpc_histogram = false
[cgroup]
path = ""
[timeouts]
"io.containerd.timeout.shim.cleanup" = "5s"
"io.containerd.timeout.shim.load" = "5s"
"io.containerd.timeout.shim.shutdown" = "3s"
"io.containerd.timeout.task.state" = "2s"
[plugins]
[plugins."io.containerd.gc.v1.scheduler"]
pause_threshold = 0.02
deletion_threshold = 0
mutation_threshold = 100
schedule_delay = "0s"
startup_delay = "100ms"
[plugins."io.containerd.grpc.v1.cri"]
disable_tcp_service = true
stream_server_address = "127.0.0.1"
stream_server_port = "0"
stream_idle_timeout = "4h0m0s"
enable_selinux = false
selinux_category_range = 1024
sandbox_image = "k8s.gcr.io/pause:3.2"
stats_collect_period = 10
systemd_cgroup = false
enable_tls_streaming = false
max_container_log_line_size = 16384
disable_cgroup = false
disable_apparmor = false
restrict_oom_score_adj = false
max_concurrent_downloads = 3
disable_proc_mount = false
unset_seccomp_profile = ""
tolerate_missing_hugetlb_controller = true
disable_hugetlb_controller = true
ignore_image_defined_volumes = false
[plugins."io.containerd.grpc.v1.cri".containerd]
snapshotter = "overlayfs"
default_runtime_name = "runc"
no_pivot = false
disable_snapshot_annotations = true
discard_unpacked_layers = false
[plugins."io.containerd.grpc.v1.cri".containerd.default_runtime]
runtime_type = ""
runtime_engine = ""
runtime_root = ""
privileged_without_host_devices = false
base_runtime_spec = ""
[plugins."io.containerd.grpc.v1.cri".containerd.untrusted_workload_runtime]
runtime_type = ""
runtime_engine = ""
runtime_root = ""
privileged_without_host_devices = false
base_runtime_spec = ""
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes]
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc]
runtime_type = "io.containerd.runc.v2"
runtime_engine = ""
runtime_root = ""
privileged_without_host_devices = false
base_runtime_spec = ""
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options]
[plugins."io.containerd.grpc.v1.cri".cni]
bin_dir = "/opt/cni/bin"
conf_dir = "/etc/cni/net.d"
max_conf_num = 1
conf_template = ""
[plugins."io.containerd.grpc.v1.cri".registry]
[plugins."io.containerd.grpc.v1.cri".registry.mirrors]
[plugins."io.containerd.grpc.v1.cri".registry.mirrors."docker.io"]
endpoint = ["https://registry-1.docker.io"]
[plugins."io.containerd.grpc.v1.cri".image_decryption]
key_model = ""
[plugins."io.containerd.grpc.v1.cri".x509_key_pair_streaming]
tls_cert_file = ""
tls_key_file = ""
[plugins."io.containerd.internal.v1.opt"]
path = "/opt/containerd"
[plugins."io.containerd.internal.v1.restart"]
interval = "10s"
[plugins."io.containerd.metadata.v1.bolt"]
content_sharing_policy