Docker was abandoned by K8S! Don't panic! Transform to Containerd in minutes

Kubernetes officially released an announcement, announcing that the support Docker Currently, the Docker support function in Kubelet is now deprecated and will be removed in a later version.

Look at the picture below (source network)

It can be seen from the above figure that the management and operation of the container by docker So, if you want to docker , then Containerd is a very good first choice.

Today, the migrant worker brother will chat with you about this open source technology Containerd.

Containerd overview

Docker Engine a long time ago, but now it is separated from the Docker Engine. As an independent open source project, the goal is to provide a more open and stable container operation infrastructure. The separated containerd will have more functions, cover all the requirements of the entire container runtime management, and provide stronger support.

Simply put, containerd is an industry-standard container runtime, which emphasizes simplicity, robustness, and portability. containerd can manage the complete container life cycle in the host, including the transmission and storage of container images, the execution and management of containers, storage and networking .

Address: https://github.com/containerd/containerd/

containerd architecture

Among them, the grpc module provides a service interface to the upper layer, and metrics provides monitoring data (cgroup-related data), and both provide services to the upper layer. containerd contains a daemon process that exposes the grpc interface through a local UNIX socket.

The storage part is responsible for the storage, management, and pull of the image. Metadata manages the container and the metadata of the image. It is stored on the disk through bootio. Task - manages the logical structure of the container, interacts with low-level event - events for container operations, The upper level can know what happened through the subscription Runtimes - low-level runtime (connected to runc)

What can Containerd do? ?

• Manage the life cycle of containers (from container creation to container destruction)
• Pull/push container image
• Storage management (manage the storage of image and container data)
• Call runC to run the container (interact with container runtimes such as runC)
• Manage container network interface and network

From the perspective of k8s, containerd is selected as the runtime component, which has a shorter call chain, fewer components, more stability, and takes up less node resources.

The above picture is from the official website of containerd. Containerd can be used as a daemon for Linux and Windows. It manages the complete container life cycle of its host system, from image transmission and storage to container execution and supervision, to low-level storage to network attachments, and so on.

installation

Download : 160cabac16e859 https://containerd.io/downloads/

[root@centos7 ~]# wget https://github.com/containerd/containerd/releases/download/v1.5.2/containerd-1.5.2-linux-amd64.tar.gz
[root@centos7 ~]# tar zxf containerd-1.5.2-linux-amd64.tar.gz -C /usr/local/

#通过上面的操作，将containerd 安装至/usr/local/bin目录下
[root@centos7 ~]# cd /usr/local/bin/
[root@centos7 bin]# ll
total 98068
-rwxr-xr-x 1 root root   214432 Mar 29 05:20 bpytop
-rwxr-xr-x 1 1001  116 49049696 May 19 12:56 containerd
-rwxr-xr-x 1 1001  116  6434816 May 19 12:56 containerd-shim
-rwxr-xr-x 1 1001  116  8671232 May 19 12:57 containerd-shim-runc-v1
-rwxr-xr-x 1 1001  116  8683520 May 19 12:57 containerd-shim-runc-v2
-rwxr-xr-x 1 1001  116 27230976 May 19 12:56 ctr
lrwxrwxrwx 1 root root        6 Mar 28 00:13 nc -> netcat
-rwxr-xr-x 1 root root   126800 Mar 28 00:13 netcat

Generate default configuration file

[root@centos7 bin]# containerd config default > /etc/containerd/config.toml
[root@centos7 bin]# ll /etc/containerd/config.toml 
-rw-r--r-- 1 root root 6069 Jun  4 14:47 /etc/containerd/config.toml

Configure containerd to run as a service

[root@centos7 ~]# touch /lib/systemd/system/containerd.service
[root@centos7 bin]# vim /lib/systemd/system/containerd.service
[Unit]
Description=containerd container runtime
Documentation=https://containerd.io
After=network.target

[Service]
ExecStartPre=/sbin/modprobe overlay
ExecStart=/usr/local/bin/containerd
Delegate=yes
KillMode=process
LimitNOFILE=1048576
# Having non-zero Limit*s causes performance problems due to accounting overhead
# in the kernel. We recommend using cgroups to do container-local accounting.
LimitNPROC=infinity
LimitCORE=infinity

[Install]
WantedBy=multi-user.target

Start service

[root@centos7 ~]# systemctl daemon-reload
[root@centos7 ~]# systemctl start containerd.service
[root@centos7 ~]# systemctl status containerd.service

containerd use

In fact, history of the lightest Kubernetes release K3s default including the containerd, Flannel, CoreDNS components.

• ctr: is the CLI of containerd itself
• crictl: is a specialized CLI tool defined by the Kubernetes community

[root@centos7 ~]# ctr version
Client:
  Version:  v1.5.2
  Revision: 36cc874494a56a253cd181a1a685b44b58a2e34a
  Go version: go1.16.4

Server:
  Version:  v1.5.2
  Revision: 36cc874494a56a253cd181a1a685b44b58a2e34a
  UUID: ebe42dac-40ae-4af1-99b0-52e61728c918

help information

[root@centos7 ~]# ctr --help
NAME:
   ctr - 
        __
  _____/ /______
 / ___/ __/ ___/
/ /__/ /_/ /
\___/\__/_/

containerd CLI


USAGE:
   ctr [global options] command [command options] [arguments...]

VERSION:
   v1.5.2

DESCRIPTION:
   
ctr is an unsupported debug and administrative client for interacting
with the containerd daemon. Because it is unsupported, the commands,
options, and operations are not guaranteed to be backward compatible or
stable from release to release of the containerd project.

COMMANDS:
   plugins, plugin            provides information about containerd plugins
   version                    print the client and server versions
   containers, c, container   manage containers
   content                    manage content
   events, event              display containerd events
   images, image, i           manage images
   leases                     manage leases
   namespaces, namespace, ns  manage namespaces
   pprof                      provide golang pprof outputs for containerd
   run                        run a container
   snapshots, snapshot        manage snapshots
   tasks, t, task             manage tasks
   install                    install a new package
   oci                        OCI tools
   shim                       interact with a shim directly
   help, h                    Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --debug                      enable debug output in logs
   --address value, -a value    address for containerd's GRPC server (default: "/run/containerd/containerd.sock") [$CONTAINERD_ADDRESS]
   --timeout value              total timeout for ctr commands (default: 0s)
   --connect-timeout value      timeout for connecting to containerd (default: 0s)
   --namespace value, -n value  namespace to use with commands (default: "default") [$CONTAINERD_NAMESPACE]
   --help, -h                   show help
   --version, -v                print the version

View and delete

[root@centos7 ~]# ctr container list
CONTAINER    IMAGE                             RUNTIME                  
nginx        docker.io/library/nginx:alpine    io.containerd.runc.v2    
[root@centos7 ~]# ctr container del nginx
[root@centos7 ~]# ctr container list
CONTAINER    IMAGE    RUNTIME   

pull image file

[root@centos7 ~]# ctr images pull docker.io/library/nginx:alpine

View the list of image files

[root@centos7 ~]# ctr images list
REF                            TYPE                                                      DIGEST                                                                  SIZE    PLATFORMS                                                                                LABELS 
docker.io/library/nginx:alpine application/vnd.docker.distribution.manifest.list.v2+json sha256:0f8595aa040ec107821e0409a1dd3f7a5e989501d5c8d5b5ca1f955f33ac81a0 9.4 MiB linux/386,linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64/v8,linux/ppc64le,linux/s390x - 

Run the container

[root@centos7 ~]# ctr run -d docker.io/library/nginx:alpine nginx
[root@centos7 ~]# ctr container list
CONTAINER    IMAGE                             RUNTIME                  
nginx        docker.io/library/nginx:alpine    io.containerd.runc.v2 

After a round of use, it is basically the same as the docker command . There is no big learning cost in use. Therefore, whether Kubernetes supports docker , for our users, there is no big problem.

For more related introductions and practical operation guides, you can refer to the official documents, which have detailed instructions for use.