Dockerfile入门
1.Dockerfile介绍
在之前Docker的使用中，我们直接从仓库下载需要的镜像到本地，然后稍加配置就可以应用了，通常从仓库下载下来的镜像都是通用的，无任何私有化的东西，我们拿过来就需要加很多的配置，每次使用就很麻烦。如果我们想定制化某一个镜像可以吗？比如Nginx，我不想每次使用都加很多的配置，而是定制化后，我再按照定制化的规则去使用，及时的安装部署我需要的Nginx环境。DockerFile就是做这个工作的，一个用基础镜像来构建新镜像的文本文件，里面包含构建镜像需要的各种指令。
使用Dockerfile构建Nginx镜像，在一个空目录下创建Dockerfile文件
[root@hadoop101 nginx]# pwd
/home/docker_test/docker_files/nginx
[root@hadoop101 nginx]# vim Dockerfile
[root@hadoop101 nginx]# ll
total 4
-rw-r--r-- 1 root root 153 Mar 29 23:33 DockerfileDockerfile内容如下：
FROM nginx
VOLUME ["volume01","volume02"]
RUN echo 'welcome,this is a nginx image of build local.' > /usr/share/nginx/html/index.html
RUN echo '----end----'
RUN /bin/bash[root@hadoop101 nginx]# docker build -t zhangbao/nginx001:1.0 .
[root@hadoop101 nginx]# docker build -t zhangbao/nginx001:1.0 .
Sending build context to Docker daemon 2.048kB
Step 1/5 : FROM nginx
---> 605c77e624dd
Step 2/5 : VOLUME ["volume01","volume02"]
---> Running in d9ff85f068bf
Removing intermediate container d9ff85f068bf
---> 801484ddbb09
Step 3/5 : RUN echo '构建本地nginx镜像' > /usr/share/nginx/html/index.html
---> Running in 6614ebace633
Removing intermediate container 6614ebace633
---> 29a385ed17b6
Step 4/5 : RUN echo '----end----'
---> Running in 3449cc6cf814
----end----
Removing intermediate container 3449cc6cf814
---> 5d6941c830a4
Step 5/5 : RUN /bin/bash
---> Running in 1f106444b093
Removing intermediate container 1f106444b093
---> 440fd4b943c7
Successfully built 440fd4b943c7
Successfully tagged zhangbao/nginx001:1.0
[root@hadoop101 nginx]#docker run -d -p 80:80 zhangbao/nginx001:1.0
首页可以查看 welcome,this is a nginx image of build local.
2. Dockerfile构建过程
构建一个新镜像，我们可以大致分为三个步骤：编写Dockerfile文件 > docker build > docker run
Dockerfile的基础知识
每个关键字（指令）都必须大写
执行过程从上到下，顺序执行
#为注释
每个指令代表一层，都会创建提交一个新的镜像层
Dockerfile指令
FROM 指定基础镜像
MAINTAINER 指定作者
RUN 执行参数中定义的命令，构建镜像时需要的命令
EXPOSE 向容器外部公开的端口号
WORKDIR 设置容器内默认工作目录
USER 指定用户
ENTROYPOINT 指定一个容器启动时运行的命令
ENV 设置环境变量
ADD|COPY 复制文件到镜像中
VOLUME 容器数据卷，向镜像创建的容器添加卷
CMD 容器启动时要运行的命令，可以有多个，但只有最后一个生效Dockerfile的构建过程就是build的执行过程
1.把当前目录和子目录当做上下文传递给docker服务，命令最后的点表示当前上下文。
2.从当前目录（不包括子目录）找到Dockerfile文件，如果不指定文件，必须是此文件名。
3.检查docker语法。
4.从基础镜像运行一个容器。
5.执行指令，修改容器，如上面操作添加数据卷，修改首页。
6.对修改后的容器提交一个新的镜像层，也可叫做中间层镜像。
7.针对中间层生成的镜像，运行新的容器。
8.重复执行修改容器、提交镜像、运行容器指令，直到所有指令执行完成。注：每条指令都会生成新的镜像，也就是生成中间层镜像，这样执行速度其实会很慢，可以不使用缓存。在构建命令中加上
--no-cache=true即可。可根据实际场景选择是否需要缓存。
3. 构建一个自己的centos
我们已经熟悉了构建Dockerfile的基础指令，现在可以做一些基本实践了。
首先我们运行一个原生的centos，然后做一些linux的基本操作
[root@hadoop101 ~]# docker run -it centos /bin/bash
[root@a0db59573b95 /]# ls
bin dev etc home lib lib64 lost+found media mnt opt proc root run sbin srv sys tmp usr var
[root@a0db59573b95 /]# ll
bash: ll: command not found
[root@a0db59573b95 /]# vim test
bash: vim: command not found
[root@a0db59573b95 /]# ifconfig
bash: ifconfig: command not found
[root@a0db59573b95 /]#可以看到，我们已经运行一个centos，然后发现一些基础的命令是没有的，这就说明这个contos是一个压缩版的，如果我们想运行一个有这些命令的镜像呢？这就需要在Dockerfile中做一些操作了？
记住在一个空白的目录下创建Dockerfile文件，我这里文件名dockerfile-mycentos，内容如下：
FROM centos
#指定作者
MAINTAINER zhangbao<zhangbaohpu@163.com>
ENV MYPATH /usr/local
WORKDIR $MYPATH
#下载需要的工具类
RUN yum -y install vim
RUN yum -y install net-tools
EXPOSE 80
CMD echo "--end--"
CMD /bin/bash如果是自定义Dockerfile文件名，则构建时必须指定文件名，否则文件名必须是：Dockerfile
[root@hadoop101 mycentos]# docker build -f dockerfile-mycentos -t mysentos:1.0 .
Sending build context to Docker daemon 2.048kB
Step 1/9 : FROM centos
---> 5d0da3dc9764
Step 2/9 : MAINTAINER zhangbao<zhangbaohpu@163.com>
---> Running in d9b4afe40ef6
Removing intermediate container d9b4afe40ef6
---> 87e522a4dcb6
Step 3/9 : ENV MYPATH /usr/local
---> Running in 2fe975209f1e
Removing intermediate container 2fe975209f1e
---> 30491c2e1634
Step 4/9 : WORKDIR $MYPATH
---> Running in cd9b1810f244
Removing intermediate container cd9b1810f244
---> d2addbefe4f6
Step 5/9 : RUN yum -y install vim
---> Running in d6a8caa012e9
CentOS Linux 8 - AppStream 64 B/s | 38 B 00:00
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist
The command '/bin/sh -c yum -y install vim' returned a non-zero code: 1
[root@hadoop101 mycentos]#这时候发现失败了，查问题是centos8的官方源已经下线了，导致yum下载失败。那刚好，我们在自定义镜像的时候可以修复这些问题。只需修改yum的默认源就可以了，这个操作也放在Dockerfile文件内。我们修复后Dockerfile文件如下：
FROM centos
#指定作者
MAINTAINER zhangbao<zhangbaohpu@163.com>
#ENV kv格式，这里指定工作目录，及默认进入容器的目录
ENV MYPATH /usr/local
WORKDIR $MYPATH
#将原有的yum配置备份下
RUN tar cvf /etc/yum.repos.d.tar /etc/yum.repos.d
#修改yum源配置，
RUN curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo
#删除掉多于的repo文件
RUN rm -rf /etc/yum.repos.d/CentOS-Linux-*
#使yum配置更新
RUN yum clean all
RUN yum makecache
#下载需要的工具类
RUN yum -y install vim
RUN yum -y install net-tools
EXPOSE 80
CMD echo "--end--"
CMD /bin/bash重新构建下修改后的Dockerfile文件
docker build -f dockerfile-mycentos -t mysentos:1.0 .
[root@hadoop101 mycentos]# docker build -f dockerfile-mycentos -t mysentos:1.0 .
Sending build context to Docker daemon 2.56kB
Step 1/14 : FROM centos
---> 5d0da3dc9764
Step 2/14 : MAINTAINER zhangbao<zhangbaohpu@163.com>
---> Running in 79ff0ddc554d
Removing intermediate container 79ff0ddc554d
---> 0cc1bf4a4ba0
Step 3/14 : ENV MYPATH /usr/local
---> Running in 59d3d432c58c
Removing intermediate container 59d3d432c58c
---> 839ed1e4b944
Step 4/14 : WORKDIR $MYPATH
---> Running in d085e4887d92
Removing intermediate container d085e4887d92
---> 41c10774900b
Step 5/14 : RUN tar cvf /etc/yum.repos.d.tar /etc/yum.repos.d
---> Running in 1ab58ab850c0
/etc/yum.repos.d/
/etc/yum.repos.d/CentOS-Linux-AppStream.repo
/etc/yum.repos.d/CentOS-Linux-BaseOS.repo
/etc/yum.repos.d/CentOS-Linux-ContinuousRelease.repo
/etc/yum.repos.d/CentOS-Linux-Debuginfo.repo
/etc/yum.repos.d/CentOS-Linux-Devel.repo
/etc/yum.repos.d/CentOS-Linux-Extras.repo
/etc/yum.repos.d/CentOS-Linux-FastTrack.repo
/etc/yum.repos.d/CentOS-Linux-HighAvailability.repo
/etc/yum.repos.d/CentOS-Linux-Media.repo
/etc/yum.repos.d/CentOS-Linux-Plus.repo
/etc/yum.repos.d/CentOS-Linux-PowerTools.repo
/etc/yum.repos.d/CentOS-Linux-Sources.repo
tar: Removing leading `/' from member names
Removing intermediate container 1ab58ab850c0
---> bfd1c4cd694c
Step 6/14 : RUN curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo
---> Running in 73ebef623f8a
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 2495 100 2495 0 0 12351 0 --:--:-- --:--:-- --:--:-- 12351
Removing intermediate container 73ebef623f8a
---> 22812c68f967
Step 7/14 : RUN rm -rf /etc/yum.repos.d/CentOS-Linux-*
---> Running in eb8426f499b0
Removing intermediate container eb8426f499b0
---> 8dc6bd0b4e84
Step 8/14 : RUN yum clean all
---> Running in a508fb503158
0 files removed
Removing intermediate container a508fb503158
---> c6831cfda20f
Step 9/14 : RUN yum makecache
---> Running in 67c3f0dc0a6a
CentOS-8.5.2111 - Base - mirrors.aliyun.com 16 MB/s | 4.6 MB 00:00
CentOS-8.5.2111 - Extras - mirrors.aliyun.com 45 kB/s | 10 kB 00:00
CentOS-8.5.2111 - AppStream - mirrors.aliyun.co 16 MB/s | 8.4 MB 00:00
Metadata cache created.
Removing intermediate container 67c3f0dc0a6a
---> 6ca3b2fbeb13
Step 10/14 : RUN yum -y install vim
---> Running in e81b9f1a4705
Last metadata expiration check: 0:00:05 ago on Tue Apr 5 09:35:43 2022.
Dependencies resolved.
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
vim-enhanced x86_64 2:8.0.1763-16.el8 AppStream 1.4 M
Installing dependencies:
gpm-libs x86_64 1.20.7-17.el8 AppStream 39 k
vim-common x86_64 2:8.0.1763-16.el8 AppStream 6.3 M
vim-filesystem noarch 2:8.0.1763-16.el8 AppStream 49 k
which x86_64 2.21-16.el8 base 49 k
Transaction Summary
================================================================================
Install 5 Packages
Total download size: 7.8 M
Installed size: 30 M
Downloading Packages:
(1/5): gpm-libs-1.20.7-17.el8.x86_64.rpm 235 kB/s | 39 kB 00:00
(2/5): which-2.21-16.el8.x86_64.rpm 203 kB/s | 49 kB 00:00
(3/5): vim-filesystem-8.0.1763-16.el8.noarch.rp 776 kB/s | 49 kB 00:00
(4/5): vim-common-8.0.1763-16.el8.x86_64.rpm 16 MB/s | 6.3 MB 00:00
(5/5): vim-enhanced-8.0.1763-16.el8.x86_64.rpm 5.4 MB/s | 1.4 MB 00:00
--------------------------------------------------------------------------------
Total 19 MB/s | 7.8 MB 00:00
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Preparing : 1/1
Installing : vim-filesystem-2:8.0.1763-16.el8.noarch 1/5
Installing : vim-common-2:8.0.1763-16.el8.x86_64 2/5
Installing : gpm-libs-1.20.7-17.el8.x86_64 3/5
Running scriptlet: gpm-libs-1.20.7-17.el8.x86_64 3/5
Installing : which-2.21-16.el8.x86_64 4/5
Installing : vim-enhanced-2:8.0.1763-16.el8.x86_64 5/5
Running scriptlet: vim-enhanced-2:8.0.1763-16.el8.x86_64 5/5
Running scriptlet: vim-common-2:8.0.1763-16.el8.x86_64 5/5
Verifying : which-2.21-16.el8.x86_64 1/5
Verifying : gpm-libs-1.20.7-17.el8.x86_64 2/5
Verifying : vim-common-2:8.0.1763-16.el8.x86_64 3/5
Verifying : vim-enhanced-2:8.0.1763-16.el8.x86_64 4/5
Verifying : vim-filesystem-2:8.0.1763-16.el8.noarch 5/5
Installed:
gpm-libs-1.20.7-17.el8.x86_64 vim-common-2:8.0.1763-16.el8.x86_64
vim-enhanced-2:8.0.1763-16.el8.x86_64 vim-filesystem-2:8.0.1763-16.el8.noarch
which-2.21-16.el8.x86_64
Complete!
Removing intermediate container e81b9f1a4705
---> 3d731b0904e6
Step 11/14 : RUN yum -y install net-tools
---> Running in f45f6c7c9c8c
Last metadata expiration check: 0:00:17 ago on Tue Apr 5 09:35:43 2022.
Dependencies resolved.
================================================================================
Package Architecture Version Repository Size
================================================================================
Installing:
net-tools x86_64 2.0-0.52.20160912git.el8 base 322 k
Transaction Summary
================================================================================
Install 1 Package
Total download size: 322 k
Installed size: 942 k
Downloading Packages:
net-tools-2.0-0.52.20160912git.el8.x86_64.rpm 934 kB/s | 322 kB 00:00
--------------------------------------------------------------------------------
Total 930 kB/s | 322 kB 00:00
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Preparing : 1/1
Installing : net-tools-2.0-0.52.20160912git.el8.x86_64 1/1
Running scriptlet: net-tools-2.0-0.52.20160912git.el8.x86_64 1/1
Verifying : net-tools-2.0-0.52.20160912git.el8.x86_64 1/1
Installed:
net-tools-2.0-0.52.20160912git.el8.x86_64
Complete!
Removing intermediate container f45f6c7c9c8c
---> adc0f183e07e
Step 12/14 : EXPOSE 80
---> Running in 9422041e18c2
Removing intermediate container 9422041e18c2
---> e94ae254891f
Step 13/14 : CMD echo "--end--"
---> Running in 9183b6a1444d
Removing intermediate container 9183b6a1444d
---> c3978bb3cb17
Step 14/14 : CMD /bin/bash
---> Running in 536c8de964d3
Removing intermediate container 536c8de964d3
---> 68f0ddc7c99f
Successfully built 68f0ddc7c99f
Successfully tagged mysentos:1.0
[root@hadoop101 mycentos]#总共分为14步，即每个指令一步，也表示每一步算一层。整个构建过程还是很详细的。
自定义镜像已经构建完成，下面我们开始运行镜像，并检测下基础命令
[root@hadoop101 mycentos]# docker run -it mysentos:1.0
[root@2f70cc22b493 local]# pwd
/usr/local
[root@2f70cc22b493 local]# ll
bash: ll: command not found
[root@2f70cc22b493 local]# vim test
[root@2f70cc22b493 local]# ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.17.0.2 netmask 255.255.0.0 broadcast 172.17.255.255
ether 02:42:ac:11:00:02 txqueuelen 0 (Ethernet)
RX packets 8 bytes 656 (656.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
loop txqueuelen 1000 (Local Loopback)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
[root@2f70cc22b493 local]#可以看到 vim 和 ifconfig 命令已经可以使用，ll 命令还需要下载对应的工具包，这里就不在下载了。
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