1 什么是镜像
镜像是一种轻量级、可执行的独立软件包，用来打包软件运行环境和基于运行环境开发的软件，它包含运行某个软件所需要的所有内容，包括代码，运行时（一个程序在运行或者在被执行的依赖）、库，环境变量和配置文件。
2 Docker镜像加载原理
Docker的镜像实际上由一层一层的文件系统组成，这种层级的文件系统是UnionFS联合文件系统。
3 分层理解
[root@iZwz99sm8v95sckz8bd2c4Z ~]# docker image inspect nginx:latest [ { “Id”: “sha256:ae2feff98a0cc5095d97c6c283dcd33090770c76d63877caa99aefbbe4343bdd”, “RepoTags”: [ “nginx:latest” ], “RepoDigests”: [ “nginx@sha256:4cf620a5c81390ee209398ecc18e5fb9dd0f5155cd82adcbae532fec94006fb9” ], “Parent”: “”, “Comment”: “”, “Created”: “2020-12-15T20:21:00.007674532Z”, “Container”: “4cc5da85f27ca0d200407f0593422676a3bab482227daee044d797d1798c96c9”, “ContainerConfig”: { “Hostname”: “4cc5da85f27c”, “Domainname”: “”, “User”: “”, “AttachStdin”: false, “AttachStdout”: false, “AttachStderr”: false, “ExposedPorts”: { “80/tcp”: {} }, “Tty”: false, “OpenStdin”: false, “StdinOnce”: false, “Env”: [ “PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin”, “NGINX_VERSION=1.19.6”, “NJS_VERSION=0.5.0”, “PKG_RELEASE=1~buster” ], “Cmd”: [ “/bin/sh”, “-c”, “#(nop) “, “CMD [“nginx” “-g” “daemon off;”]” ], “Image”: “sha256:13bffe371b56f4aeed88218ec17d0c6f653a83b49bd3e211fc8cfa2ca5d7a3d3”, “Volumes”: null, “WorkingDir”: “”, “Entrypoint”: [ “/docker-entrypoint.sh” ], “OnBuild”: null, “Labels”: { “maintainer”: “NGINX Docker Maintainers docker-maint@nginx.com” }, “StopSignal”: “SIGQUIT” }, “DockerVersion”: “19.03.12”, “Author”: “”, “Config”: { “Hostname”: “”, “Domainname”: “”, “User”: “”, “AttachStdin”: false, “AttachStdout”: false, “AttachStderr”: false, “ExposedPorts”: { “80/tcp”: {} }, “Tty”: false, “OpenStdin”: false, “StdinOnce”: false, “Env”: [ “PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin”, “NGINX_VERSION=1.19.6”, “NJS_VERSION=0.5.0”, “PKG_RELEASE=1~buster” ], “Cmd”: [ “nginx”, “-g”, “daemon off;” ], “Image”: “sha256:13bffe371b56f4aeed88218ec17d0c6f653a83b49bd3e211fc8cfa2ca5d7a3d3”, “Volumes”: null, “WorkingDir”: “”, “Entrypoint”: [ “/docker-entrypoint.sh” ], “OnBuild”: null, “Labels”: { “maintainer”: “NGINX Docker Maintainers docker-maint@nginx.com” }, “StopSignal”: “SIGQUIT” }, “Architecture”: “amd64”, “Os”: “linux”, “Size”: 132935043, “VirtualSize”: 132935043, “GraphDriver”: { “Data”: { “LowerDir”: “/var/lib/docker/overlay2/cb791e78a08db7091bf2ce1d78603f1758f52199e57f1805156fe30e39067aae/diff:/var/lib/docker/overlay2/1e73a72b25af68ee9abf4eb443f778d31226e12e9af428fcc14c7b044c83b258/diff:/var/lib/docker/overlay2/88c9c01762f2af8327db65d0b0d4a64785e87c9c2ab76c62e7d03619db03a985/diff:/var/lib/docker/overlay2/7304ab112ac4a9cb91fc6f74730be28fecbe19f042e92d321aa9181424cc4b2e/diff”, “MergedDir”: “/var/lib/docker/overlay2/48b288740bbb2b07b41ed43a4d17a005c46b08d3357d2960b5ef7db4b2de6618/merged”, “UpperDir”: “/var/lib/docker/overlay2/48b288740bbb2b07b41ed43a4d17a005c46b08d3357d2960b5ef7db4b2de6618/diff”, “WorkDir”: “/var/lib/docker/overlay2/48b288740bbb2b07b41ed43a4d17a005c46b08d3357d2960b5ef7db4b2de6618/work” }, “Name”: “overlay2” }, “RootFS”: { “Type”: “layers”, “Layers”: [ “sha256:87c8a1d8f54f3aa4e05569e8919397b65056aa71cdf48b7f061432c98475eee9”, “sha256:5c4e5adc71a82a96f02632433de31c998c5a9e2fccdcbaee780ae83158fac4fa”, “sha256:7d2b207c26790f693ab1942bbe26af8e2b6a14248969e542416155a912fec30d”, “sha256:2c7498eef94aef8c40d106f3e42f7da62b3eee8fd36012bf7379becc4cd639a2”, “sha256:4eaf0ea085df254fd5d2beba4e2c11db70a620dfa411a8ad44149e26428caee4” ] },
“Metadata”: { “LastTagTime”: “0001-01-01T00:00:00Z” } } ] }
这里指示了分层信息：
4 提交镜像
使用docker commit 命令提交容器成为一个新的版本
docker commit -m=“提交的描述信息” -a=”作者” 容器id 目标镜像名:[TAG]
由于默认的Tomcat镜像的webapps文件夹中没有任何内容，需要从webapps.dist中拷贝文件到webapps文件夹。下面自行制作镜像：就是从webapps.dist中拷贝文件到webapps文件夹下，并提交该镜像作为一个新的镜像。使得该镜像默认的webapps文件夹下就有文件。具体命令如下：
#1.复制文件夹 [root@iZwz99sm8v95sckz8bd2c4Z ~]# docker run -it tomcat /bin/bash root@2a3bf3eaa2e4:/usr/local/tomcat# cd webapps root@2a3bf3eaa2e4:/usr/local/tomcat/webapps# ls root@2a3bf3eaa2e4:/usr/local/tomcat/webapps# cd ../ root@2a3bf3eaa2e4:/usr/local/tomcat# cp -r webapps.dist/* webapps root@2a3bf3eaa2e4:/usr/local/tomcat# cd webapps root@2a3bf3eaa2e4:/usr/local/tomcat/webapps# ls ROOT docs examples host-manager manager [root@iZwz99sm8v95sckz8bd2c4Z ~]# docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 2a3bf3eaa2e4 tomcat “/bin/bash” 4 minutes ago Up 4 minutes 8080/tcp competent_torvalds 7789d4505a00 portainer/portainer “/portainer” 24 hours ago Up 24 hours 0.0.0.0:8088->9000/tcp quirky_sinoussi [root@iZwz99sm8v95sckz8bd2c4Z ~]# docker exec -it 2a3bf3eaa2e4 /bin/bash root@2a3bf3eaa2e4:/usr/local/tomcat# cd webapps root@2a3bf3eaa2e4:/usr/local/tomcat/webapps# ls ROOT docs examples host-manager manager root@2a3bf3eaa2e4:/usr/local/tomcat/webapps# cd ../ root@2a3bf3eaa2e4:/usr/local/tomcat# read escape sequence [root@iZwz99sm8v95sckz8bd2c4Z ~]# docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 2a3bf3eaa2e4 tomcat “/bin/bash” 8 minutes ago Up 8 minutes 8080/tcp competent_torvalds 7789d4505a00 portainer/portainer “/portainer” 24 hours ago Up 24 hours 0.0.0.0:8088->9000/tcp quirky_sinoussi
#2.提交镜像作为一个新的镜像
[root@iZwz99sm8v95sckz8bd2c4Z ~]# docker commit -m=”add webapps” -a=”Ethan” 2a3bf3eaa2e4 mytomcat:1.0 sha256:f189aac861de51087af5bc88a5f1de02d9574e7ee2d163c647dd7503a2d3982b [root@iZwz99sm8v95sckz8bd2c4Z ~]# docker images REPOSITORY TAG IMAGE ID CREATED SIZE mytomcat 1.0 f189aac861de 7 seconds ago 653MB mysql 5.7 f07dfa83b528 6 days ago 448MB tomcat latest feba8d001e3f 10 days ago 649MB nginx latest ae2feff98a0c 12 days ago 133MB centos latest 300e315adb2f 2 weeks ago 209MB portainer/portainer latest 62771b0b9b09 5 months ago 79.1MB elasticsearch 7.6.2 f29a1ee41030 9 months ago 791MB
#3.运行容器
[root@iZwz99sm8v95sckz8bd2c4Z ~]# docker run -it mytomcat:1.0 /bin/bash root@1645774d4605:/usr/local/tomcat# cd webapps root@1645774d4605:/usr/local/tomcat/webapps# ls ROOT docs examples host-manager manager wz99sm8v95sckz8bd2c4Z ~]# docker images REPOSITORY TAG IMAGE ID CREATED SIZE mytomcat 1.0 f189aac861de 7 seconds ago 653MB mysql 5.7 f07dfa83b528 6 days ago 448MB tomcat latest feba8d001e3f 10 days ago 649MB nginx latest ae2feff98a0c 12 days ago 133MB centos latest 300e315adb2f 2 weeks ago 209MB portainer/portainer latest 62771b0b9b09 5 months ago 79.1MB elasticsearch 7.6.2 f29a1ee41030 9 months ago 791MB
原文链接：https://blog.51cto.com/u_15689290/5569217
