利用docker commit命令生成镜像
Docker镜像是多层存储，每一层是在前一层的基础上进行的修改。而容器是镜像为基础层的多层存储。
如果不使用数据卷，运行一个容器的时候，对任何文件的修改都会被记录于容器存储层。
docker commit 命令可以将容器存储层保存下来成为镜像。也就将原有镜像的基础层和容器存储层，并构成包含原有容器最后的文件变化的新镜像。
但在实际环境中，推荐使用Dockerfile来完成定制镜像，而不是使用docker commit 命令。
原因如下：
- 大量的无关内容被添加进来，如果不小心清理，将会导致镜像极为臃肿。
- 使用 docker commit命令生成的是黑箱镜像，除了制作镜像的作者清楚具体的改动，他人只能通过docker diff命令获取很少的线索，难以维护。
示例：
[root@CentOS-7 ~]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
docker.io/ubuntu latest 6a2f32de169d 6 days ago 117.2 MB
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker run --name TestCommitImages -d -it ubuntu bash
ca9cb66a39ca0271149fadce05523d41488a5c047196de510fe54c0f26a46b25
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ca9cb66a39ca ubuntu "bash" 4 seconds ago Up 2 seconds TestCommitImages
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker exec -it TestCommitImages bash
root@ca9cb66a39ca:/# echo "this is a test !" >> testcommit.log
root@ca9cb66a39ca:/# ls -l testcommit.log
-rw-r--r-- 1 root root 17 Apr 19 03:04 testcommit.log
root@ca9cb66a39ca:/# cat testcommit.log
this is a test !
root@ca9cb66a39ca:/# exit
exit
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker diff TestCommitImages
C /run
A /run/secrets
C /root
A /root/.bash_history
A /testcommit.log
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker commit --author "anliven" --message "touch new file" TestCommitImages ubuntu:commit
sha256:87575bc0c80f7dd9230072626a31cdeea5c6163e70b559f5432eaac881bd2376
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker images ubuntu
REPOSITORY TAG IMAGE ID CREATED SIZE
ubuntu commit 87575bc0c80f 36 seconds ago 117.2 MB
docker.io/ubuntu latest 6a2f32de169d 6 days ago 117.2 MB
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker history ubuntu:commit
IMAGE CREATED CREATED BY SIZE COMMENT
87575bc0c80f 9 minutes ago bash 106 B touch new file
6a2f32de169d 6 days ago /bin/sh -c #(nop) CMD ["/bin/bash"] 0 B
<missing> 6 days ago /bin/sh -c mkdir -p /run/systemd && echo 'doc 7 B
<missing> 6 days ago /bin/sh -c sed -i 's/^#s*(deb.*universe)$/ 2.759 kB
<missing> 6 days ago /bin/sh -c rm -rf /var/lib/apt/lists/* 0 B
<missing> 6 days ago /bin/sh -c set -xe && echo '#!/bin/sh' > /u 745 B
<missing> 6 days ago /bin/sh -c #(nop) ADD file:b8a2c16d65e533a2bc 117.2 MB
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker run --name NewImages -it ubuntu:commit bash
root@cfa4b8cf7d2c:/# ls -l testcommit.log
-rw-r--r-- 1 root root 17 Apr 19 03:04 testcommit.log
root@cfa4b8cf7d2c:/# cat testcommit.log
this is a test !
root@cfa4b8cf7d2c:/# exit
exit
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
cfa4b8cf7d2c ubuntu:commit "bash" 2 hours ago Exited (0) 6 seconds ago NewImages
ca9cb66a39ca ubuntu "bash" 2 hours ago Up 2 hours TestCommitImages
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# docker logs NewImages
root@cfa4b8cf7d2c:/# ls -l testcommit.log
-rw-r--r-- 1 root root 17 Apr 19 03:04 testcommit.log
root@cfa4b8cf7d2c:/# cat testcommit.log
this is a test !
root@cfa4b8cf7d2c:/# exit
exit
[root@CentOS-7 ~]#