Docker basics!

Docker overview

Docker is an open source tool for running applications in Linux. It is a lightweight virtual machine. It was born in 2013. Its original initiator is dotCloud company. Its design purpose is "Build, Ship and Run Any App,Anywhere", that is, through the management of the life cycle of application packaging, release, deployment and operation, it can achieve "one-time packaging" at the application component level, "Run everywhere"

The difference between Docker and traditional virtualization

characteristicDocker containervirtual machine
Computing power lossAlmost noneThe loss is about 50%
performanceNear primaryWeaker than primary
Single machine quantity supported by the systemHundreds ofDozens
IsolationResource limitation (process isolation)Complete isolation
Disk occupancyMBGB

Docker principle

cgroup (resource control) and namespace (namespace) are two components, which control and manage six namespaces

6 namespaces:

  • User: the user and user group of the operation process
  • net: network equipment and port
  • pid: process number
  • uts: host name and main sentence field
  • ipc: memory space used for communication between applications
  • Mount: file system and mount point

Docker three components

  • Image: a collection of resources, including applications, related dependent packages and running environments, which is equivalent to the template of the container
  • Container: a run-time state based on a mirror image. Each container is isolated from each other
  • Warehouse: store image images

Docker network mode

  • HOST mode: the docker container does not have its own network card and IP, but uses the IP and port of the HOST, and shares a network namespace with the HOST. Its greatest advantage is that the network performance is relatively good, but because it uses the IP address of the HOST directly, its isolation is not good and its security is relatively low
  • Container mode: the container does not create its own network card and IP, but shares the IP and port range with a specified container. It does not share the IP address with the host. Compared with the host mode, the security is higher. The processes of the two containers can communicate through the lo:0 network card device
  • None mode: in this mode, the container has only lo loopback network card, and the network function is turned off
  • Bridge mode: this mode will set the IP address for each container, connect the container to a docker virtual network, communicate with the host through the docker0 bridge and the nat table configuration of iptables, and allocate an IP from the docker0 subnet to the container

Dockerfile

  • Each instruction in Dockerfile creates a new mirror layer
  • The mirror layer will be cached and reused (the former layer will be cached for the later layer)
  • When the Dockerfile instruction is modified, the copied file changes, or the specified variables are different when building the image, the corresponding image layer cache will become invalid
  • After a layer's image cache is invalidated, all its image layer caches will be invalidated. The image layer is immutable. If a file is added in one layer and then deleted in the next layer, the file will still be included in the image

Layering of Docker image

The docker image is built based on AUFS (which can combine the contents of multiple files)

Docker installation and deployment

##Install dependent packages
[root@docker ~]# yum install -y yum-utils device-mapper-persistent-data lvm2

##Set alicloud image source
[root@docker ~]# cd /etc/yum.repos.d/
[root@docker yum.repos.d]# yum-config-manager --add-repo https://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo

##Install docker CE Community Edition
[root@docker yum.repos.d]# yum install -y docker-ce

[root@docker yum.repos.d]# systemctl start docker
[root@docker yum.repos.d]# systemctl enable docker
Created symlink from /etc/systemd/system/multi-user.target.wants/docker.service to /usr/lib/systemd/system/docker.service.

##Here, we do not need the image warehouse for the time being, but set the image acceleration. The image acceleration can be obtained free of charge at Alibaba
[root@docker yum.repos.d]# mkdir -p /etc/docker
[root@docker yum.repos.d]# tee /etc/docker/daemon.json <<-'EOF'
> {
>   "registry-mirrors": ["https://r4f0p1ia.mirror.aliyuncs.com"]
> }
> EOF

[root@docker yum.repos.d]# systemctl daemon-reload
[root@docker yum.repos.d]# systemctl restart docker

##network optimization 
[root@docker yum.repos.d]# vim /etc/sysctl.conf
net.ipv4.ip_forward=1
[root@docker yum.repos.d]# systemctl restart network
[root@docker yum.repos.d]# systemctl restart docker

##Modify profile
[root@docker yum.repos.d]# cd /etc/docker/
[root@docker docker]# ls
daemon.json  key.json
[root@docker docker]# vim daemon.json 	##Add the following
{
 "graph": "/data/docker",							##Data directory
 "storage-driver": "overlay2",						##Storage engine
 "insecure-registries": ["registry.access.redhat.com","quary.io"]		##Private warehouse
 "regustry-mirrors": ["https://r4f0p1ia.mirror.aliyuncs.com"] 			## Image acceleration			
 "bip": "172.7.5.1/24",								##docker network
 "exec-opts": ["native.cgroupdriver-systemd"],		##Additional parameters at startup
 "live-restore": true								
}

Docker command

Manage mirroring

##View docker version
[root@docker yum.repos.d]# docker -v
Docker version 20.10.8, build 3967b7d

##Download the image from the official docker hub
[root@docker docker]# docker pull hello-world:latest		
latest: Pulling from library/hello-world
b8dfde127a29: Pull complete 
Digest: sha256:7d91b69e04a9029b99f3585aaaccae2baa80bcf318f4a5d2165a9898cd2dc0a1
Status: Downloaded newer image for hello-world:latest
docker.io/library/hello-world:latest

##View mirror
[root@docker docker]# docker images
REPOSITORY    TAG       IMAGE ID       CREATED        SIZE
hello-world   latest    d1165f221234   5 months ago   13.3kB

##Run mirror
[root@docker docker]# docker run hello-world

##Search image
[root@docker ~]# docker search nginx

##View image information
[root@docker ~]# Docker inspect d1165f222234 (container ID)

##Label the image
[root@docker ~]# docker tag hello-world:latest hello-world:whd
[root@docker ~]# docker images
REPOSITORY    TAG       IMAGE ID       CREATED        SIZE
hello-world   latest    d1165f221234   6 months ago   13.3kB
hello-world   whd       d1165f221234   6 months ago   13.3kB
centos        7         8652b9f0cb4c   9 months ago   204MB

##Delete image, docker rmi image name / label
[root@docker ~]# docker rmi hello-world:whd
Untagged: hello-world:whd
[root@docker ~]# docker images
REPOSITORY    TAG       IMAGE ID       CREATED        SIZE
hello-world   latest    d1165f221234   6 months ago   13.3kB
centos        7         8652b9f0cb4c   9 months ago   204MB

##Export image as file
[root@docker ~]# docker save -o hello-world hello-world:latest 
[root@docker ~]# ls
anaconda-ks.cfg  hello-world  initial-setup-ks.cfg  Public template video picture document download music desktop
[root@docker ~]# scp hello-world root@192.168.118.88:/opt	##Incoming to another server
[root@node2 opt]# docker load < hello-world 				##Import mirror
f22b99068db9: Loading layer [==================================================>]  15.36kB/15.36kB
Loaded image: hello-world:latest
[root@node2 opt]# docker images
REPOSITORY    TAG       IMAGE ID       CREATED        SIZE
hello-world   latest    d1165f221234   6 months ago   13.3kB

Container operation

[root@docker ~]# docker run hello-world		##Run a mirror as a container
[root@docker ~]# docker ps -a				##View all container status
CONTAINER ID   IMAGE         COMMAND    CREATED          STATUS                      PORTS     NAMES
f5d09aed4e48   hello-world   "/hello"   11 seconds ago   Exited (0) 10 seconds ago             festive_wiles
[root@docker ~]# docker rm f5d09aed4e48		##Delete containers. Only those that are not running can be deleted. Add - f to force the deletion of running containers			
f5d09aed4e48
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES

##Create container
[root@docker ~]# docker create -it nginx:latest /bin/bash
978de36e212ce0611030e85f3c45dac885bed07989dcbefcee7ba4d79b482d8e
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED         STATUS    PORTS     NAMES
978de36e212c   nginx:latest   "/docker-entrypoint...."   7 seconds ago   Created             dazzling_pascal
[root@docker ~]# docker start 978de36e212c   		##Start container based on container ID
978de36e212c
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS         PORTS     NAMES
978de36e212c   nginx:latest   "/docker-entrypoint...."   23 seconds ago   Up 3 seconds   80/tcp    dazzling_pascal

##Create container at once
[root@docker ~]# docker run centos:7 /usr/bin/bash -c ls /
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS                      PORTS     NAMES
720bc6dc8403   centos:7       "/usr/bin/bash -c ls..."   13 seconds ago   Exited (0) 12 seconds ago             romantic_khorana
978de36e212c   nginx:latest   "/docker-entrypoint...."   14 minutes ago   Up 13 minutes               80/tcp    dazzling_pascal

##Stop container
[root@docker ~]# docker stop 978de36e212c
978de36e212c
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS                       PORTS     NAMES
720bc6dc8403   centos:7       "/usr/bin/bash -c ls..."   3 minutes ago    Exited (0) 3 minutes ago               romantic_khorana
978de36e212c   nginx:latest   "/docker-entrypoint...."   18 minutes ago   Exited (137) 6 seconds ago             dazzling_pascal

##Continuous background operation
[root@docker ~]# docker run -d centos:7 /usr/bin/bash -c "while true;do echo hello;done"
4f3e6ae802c124acd0ae2927f00f51aba0d95aaaf315fac5ac1be1d0dc3e4694
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS                       PORTS     NAMES
4f3e6ae802c1   centos:7       "/usr/bin/bash -c 'w..."   6 seconds ago    Up 5 seconds                           musing_chaplygin
720bc6dc8403   centos:7       "/usr/bin/bash -c ls..."   9 minutes ago    Exited (0) 8 minutes ago               romantic_khorana
978de36e212c   nginx:latest   "/docker-entrypoint...."   23 minutes ago   Exited (137) 5 minutes ago             dazzling_pascal

##Enter container
[root@docker ~]# docker exec -it 4f3e6ae802c1 /bin/bash		#The container must be open
[root@4f3e6ae802c1 /]# exit				#To exit the container, you can also use ctrl+d

##Export container
[root@docker ~]# docker export 720bc6dc8403 > centos7_01
[root@docker ~]# ls
anaconda-ks.cfg  centos7_01  hello-world  initial-setup-ks.cfg  Public template video picture document download music desktop
[root@docker ~]# docker import centos7_01 centos:7		##To import a container to generate an image, delete the original image first
sha256:b8fd67de266efab02246838b6fa0579f9d7371a0a22b757a242de1dd9e276c03
[root@docker ~]# docker images
REPOSITORY    TAG       IMAGE ID       CREATED         SIZE
centos        7         b8fd67de266e   8 seconds ago   204MB
nginx         latest    822b7ec2aaf2   3 hours ago     133MB
hello-world   latest    d1165f221234   6 months ago    13.3kB

Network management

[root@docker ~]# docker network ls				##View network list
NETWORK ID     NAME      DRIVER    SCOPE
27c66017f197   bridge    bridge    local
81e631b13efa   host      host      local
f330b96785dc   none      null      local

##Custom network
[root@docker ~]# docker network create --subnet=172.18.0.0/16 mynetwork		#No network mode is specified. The default is bridge
[root@docker ~]# docker network ls
NETWORK ID     NAME        DRIVER    SCOPE
27c66017f197   bridge      bridge    local
81e631b13efa   host        host      local
da866d133585   mynetwork   bridge    local
f330b96785dc   none        null      local
[root@docker ~]# docker run -itd --name test2 --net mynetwork --ip 172.18.0.100 centos:7 /bin/bash
fdd8a497d4daa9f89976da05ed4f25dbb89fe15347930738dcc5bbe803083cb1

##Add nginx service and set nat port mapping
[root@docker ~]# docker run -itd --name nginx_01 --network mynetwork --ip 172.18.0.10 nginx:latest /bin/bash
66b34e794169a7817057b10afce835103136c600220d5e9075a9605664b3de87
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS          PORTS     NAMES
66b34e794169   nginx:latest   "/docker-entrypoint...."   12 seconds ago   Up 11 seconds   80/tcp    nginx_01
fdd8a497d4da   centos:7       "/bin/bash"              25 minutes ago   Up 25 minutes             test2
[root@docker ~]# docker run -itd -p 333:80 nginx /bin/bash		##Specifies the port mapping fixed IP address
068caa856ec34884b9962b6cc6e8a171f3658dce22184adf0db49bf403ec3caa
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED              STATUS              PORTS                                 NAMES
068caa856ec3   nginx          "/docker-entrypoint...."   About a minute ago   Up About a minute   0.0.0.0:333->80/tcp, :::333->80/tcp   awesome_curie
66b34e794169   nginx:latest   "/docker-entrypoint...."   5 minutes ago        Up 5 minutes        80/tcp                                nginx_01
fdd8a497d4da   centos:7       "/bin/bash"              30 minutes ago       Up 30 minutes                                             test2
[root@docker ~]# docker exec 068caa856ec3 nginx			#Running services

View in browser

[root@docker ~]#  docker run -itd -P nginx /bin/bash		##Use capital P to indicate random port mapping
ea84118985ca363917b41da6829d263ae344a8b283f79c476b6271ce7ea3155b
[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS          PORTS                                     NAMES
ea84118985ca   nginx          "/docker-entrypoint...."   49 seconds ago   Up 48 seconds   0.0.0.0:49153->80/tcp, :::49153->80/tcp   nice_meitner
068caa856ec3   nginx          "/docker-entrypoint...."   5 minutes ago    Up 5 minutes    0.0.0.0:333->80/tcp, :::333->80/tcp       awesome_curie
66b34e794169   nginx:latest   "/docker-entrypoint...."   9 minutes ago    Up 9 minutes    80/tcp                                    nginx_01
fdd8a497d4da   centos:7       "/bin/bash"              35 minutes ago   Up 35 minutes  
[root@docker ~]# docker exec ea84118985ca nginx

##Specify the container as a privileged container
[root@docker ~]# docker run -itd --name centos-systemd --privileged=true centos:7 /sbin/init
55a1a7c675bcc22c5f33b48cba54779482d0106c0183fc19a7417e229644d66c
[root@docker ~]# docker exec -it fdd8a497d4da /bin/bash
[root@55a1a7c675bc /]# yum install -y httpd
[root@55a1a7c675bc /]# systemctl start httpd 
[root@55a1a7c675bc /]# systemctl status httpd
‚óŹ httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
   Active: active (running) since Sat 2021-09-04 11:32:36 UTC; 20s ago
..............................

Docker data volume

  • Data volume: realize data sharing between host and container
  • Data volume container: realize data sharing between containers
##Host / var/www mounts / data1 and / var/html mounts / data2 in the container
[root@docker ~]# docker run -v /var/www:/data1 -v /var/html:/data2 --name centos_v1 -it centos:7 /bin/bash 
[root@8d19fd5f44a2 /]# ls				##View automatically created data1 and data2
anaconda-post.log  bin  data1  data2  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

##Create files in two directories of the container
[root@8d19fd5f44a2 /]# cd data1/
[root@8d19fd5f44a2 data1]# touch txt.1
[root@8d19fd5f44a2 data1]# ls
txt.1
[root@8d19fd5f44a2 data1]# cd ../data2/
[root@8d19fd5f44a2 data2]# touch txt.2
[root@8d19fd5f44a2 data2]# ls
txt.2

##Return to host view
[root@8d19fd5f44a2 data2]# exit
[root@docker ~]# cd /var/www/
[root@docker www]# ls
txt.1
[root@docker www]# cd /var/html/
[root@docker html]# ls
txt.2

##Create a data volume container and specify that the volume is from centos_01
[root@docker html]# docker run -it --volumes-from centos_v1 --name db1 centos:7 /bin/bash
[root@aa687b5b14ba /]# cd data1/
[root@aa687b5b14ba data1]# ls   
txt.1

##Container interconnection (delete all containers created earlier first)
[root@docker html]# docker run -itd --name centos_01 centos:7 /bin/bash
f7695de3066212eb55b275b23cd97ed0aa83e28016e3bb51f42e8cfc9783c5a7
[root@docker html]# docker run -itd --name centos_02 --link centos_01:centos_01 centos:7 /bin/bash
##--link setting centos_01 and centos_02 interconnection
b7b1a5c49eb00338c0d0a46b05837d0d2310f9a78b85c0df3ca1ce0c2e844bf6
[root@docker html]# docker ps -a
CONTAINER ID   IMAGE      COMMAND       CREATED         STATUS         PORTS     NAMES
b7b1a5c49eb0   centos:7   "/bin/bash"   2 minutes ago   Up 2 minutes             centos_02
f7695de30662   centos:7   "/bin/bash"   6 minutes ago   Up 6 minutes             centos_01
[root@docker html]# docker inspect --format='{{.NetworkSettings.IPAddress}}' b7b1a5c49eb0 
##View centos_02 container IP address
172.17.0.3
[root@docker html]# docker exec -it f7695de30662 /bin/bash		#Enter centos_01 container
[root@f7695de30662 /]# yum install -y net-tools					#Download the ifconfig tool, or use ipconfig to view the IP address
[root@f7695de30662 /]# ping 172.17.0.3							#
PING 172.17.0.3 (172.17.0.3) 56(84) bytes of data.
64 bytes from 172.17.0.3: icmp_seq=1 ttl=64 time=0.111 ms
64 bytes from 172.17.0.3: icmp_seq=2 ttl=64 time=0.056 ms
64 bytes from 172.17.0.3: icmp_seq=3 ttl=64 time=0.057 ms

Keywords: Linux Operation & Maintenance Docker

Added by Mindwreck on Sat, 04 Sep 2021 20:51:26 +0300