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Docker ❀ DockerFile - Docker的重中之重


文章目录

  • ​​1、基础概念​​
  • ​​2、构建过程​​
  • ​​(1)语法介绍​​
  • ​​(2)DockerFile的执行流程​​
  • ​​3、体系结构​​
  • ​​4、案例配置​​
  • ​​(1)案例一:构建自定义系统​​
  • ​​(2)案例二:区分CMD与ENTRYPOINT指令​​

1、基础概念

DockerFile是用来构建Docker镜像的构建文件,是由一系列命令和参数构成的脚本;我们在https://hub.docker.com/爬取的镜像其实本身也是由DockerFile文件构建,如下所示;
Docker ❀ DockerFile - Docker的重中之重_xss

搜索引擎内搜查centos,选择某一个镜像,点击;
Docker ❀ DockerFile - Docker的重中之重_xss_02

查找到对应的镜像版本与其DockerFile链接;
Docker ❀ DockerFile - Docker的重中之重_xss_03

DockerFile链接为Github网站内代码;
Docker ❀ DockerFile - Docker的重中之重_centos_04

代码如下:

FROM scratch            /镜像本源;
ADD centos-8-x86_64.tar.xz /
LABEL org.label-schema.schema-version="1.0" org.label-schema.name="CentOS Base Image"org.label-schema.vendor="CentOS" org.label-schema.license="GPLv2" org.labelschema.build-date="20201204"
CMD ["/bin/bash"]

2、构建过程

DockerFile构建镜像的过程如下:

  • 编写DockerFile文件
  • docker build
  • docker run

(1)语法介绍

每条保留字指令都必须为大写字母且后面要跟随至少一个参数;

  • 指令按照从上到下的顺序执行;
  • ​# 代表注释;​
  • 每条指令都会创建一个新的镜像层,并对镜像进行提交;

(2)DockerFile的执行流程

Docker从基础镜像运行一个容器;

  • 执行一条指令并对容器做出修改;
  • 执行类似Docker commit的操作提交一个新的镜像层;
  • Docker再基于刚提交的镜像运行一个新容器;
  • 执行DockerFile中的下一条指令直到所有指令都执行完成;

3、体系结构

保留字指令

  • FROM:基础镜像,指定当前镜像是基于哪个镜像的;
  • MAINTAINER:指定镜像维护者的姓名和邮箱地址;
  • RUN:指定容器构建时需要运行的命令;
  • EXPOSE:指定当前容器对外暴露的端口信息;
  • WORKDIR:指定在创建容器后终端默认登录的工作目录;
  • ENV:指定构建镜像过程中的环境变量;
  • ADD:将宿主机目录下文件复制进镜像且ADD命令会自动处理URL和解压tar类型压缩包;
  • COPY:类似于ADD,复制文件和目录到镜像中,但是不做处理;
    – CPOY src dest
    – COPY [“src”,“dest”]
  • VOLUME:容器数据卷,用于数据保持和持久化;
  • CMD:指定容器启动时要运行的命令,Docker中可以存在多个CMD命令,但是只有最后一个生效,CMD会被Docker run之后的参数替换;
  • ENTRYPOINT:指定容器启动时要运行的命令,ENTRYPOINT和CMD一样,但是不会被Docker run的参数替换,进行追加执行;
  • ONBUILD:当构建一个被继承的DockerFile时运行指令,父镜像在被子镜像继承后父镜像的onbuild被触发;

4、案例配置

(1)案例一:构建自定义系统

首先使用默认centos镜像创建一个容器作为对比容器,名称设置为test_a,在该容器内执行vim与ifconfig命令无法执行,因为精简版的centos没有此功能;

[root@Docker ~]# docker run -it --name test_a centos
[root@efb048390050 /]# pwd
/
[root@efb048390050 /]# vim /tmp/test.txt
bash: vim: command not found
[root@efb048390050 /]# ifconfig
bash: ifconfig: command not found

构建DockerFile;

[root@Docker ~]# vim /myDocker/DockerFile_test01 
FROM centos
MAINTAINER zxc<497427805@qq.com>
ENV mypath /tmp /环境变量设置为/tmp;
WORKDIR $mypath /修改容器默认登录目录;

RUN yum install -y vim /安装vim功能;
RUN yum install -y net-tools /安装网络功能;

EXPOSE 80 /暴露80端口;
CMD /bin/bash

使用DockerFile构建镜像;

[root@Docker ~]# docker build -f /myDocker/DockerFile_test01 -t mycentos:1.3 .
Sending build context to Docker daemon 12.19MB
Step 1/8 : FROM centos
---> 300e315adb2f
Step 2/8 : MAINTAINER zxc<497427805@qq.com>
---> Running in 9334196fed84
Removing intermediate container 9334196fed84
---> 3faa116ae7ee
Step 3/8 : ENV mypath /tmp
---> Running in 63dbd47292ce
Removing intermediate container 63dbd47292ce
---> def729e0a375
Step 4/8 : WORKDIR $mypath
---> Running in 5e2756007a93
Removing intermediate container 5e2756007a93
---> 422d53f849bd
Step 5/8 : RUN yum install -y vim
Complete!
Removing intermediate container 0448e9cb3db8
---> d761096df2eb
Step 6/8 : RUN yum install -y net-tools
Complete!
Removing intermediate container 948beabdd09e
---> 4d7ccf0941d4
Step 7/8 : EXPOSE 80
---> Running in f5870f895b8f
Removing intermediate container f5870f895b8f
---> 78d5fca3e1dd
Step 8/8 : CMD /bin/bash
---> Running in a991211763cc
Removing intermediate container a991211763cc
---> 37fa47ba5db8
Successfully built 37fa47ba5db8
Successfully tagged mycentos:1.3

[root@Docker ~]# docker images mycentos
REPOSITORY TAG IMAGE ID CREATED SIZE
centos latest 300e315adb2f 3 months ago 209MB
mycentos 1.3 37fa47ba5db8 2 minutes ago 291MB

使用新镜像创建容器,名称为test_b,并验证容器默认登录目录、vim与ifconfig是否可以执行、端口80是否打开;

[root@Docker ~]# docker run -it --name test_b mycentos:1.3 
[root@3663701a12aa tmp]# pwd
/tmp
[root@3663701a12aa tmp]# vim /tmp/test.txt
[root@3663701a12aa tmp]# ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.17.0.3 netmask 255.255.0.0 broadcast 172.17.255.255
ether 02:42:ac:11:00:03 txqueuelen 0 (Ethernet)
RX packets 16 bytes 2092 (2.0 KiB)
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@3663701a12aa tmp]# [root@Docker ~]#
[root@Docker ~]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3663701a12aa mycentos:1.3 "/bin/sh -c /bin/bash" 24 seconds ago Up 22 seconds 80/tcp test_b
efb048390050 centos "/bin/bash" 8 minutes ago Up 8 minutes test_a

(2)案例二:区分CMD与ENTRYPOINT指令

[root@Docker ~]# vim /myDocker/DockerFile_test02 
FROM centos
RUN yum install -y curl
CMD curl -k https://www.baidu.com

[root@Docker ~]# docker build -f /myDocker/DockerFile_test02 -t mycentos02:1.3 .
Sending build context to Docker daemon 12.19MB
Step 1/3 : FROM centos
---> 300e315adb2f
Step 2/3 : RUN yum install -y curl
Complete!
Removing intermediate container 9d958771849f
---> 2c4160ab22b9
Step 3/3 : CMD curl -s http://ip.cn
---> Running in 6419f0667627
Removing intermediate container 6419f0667627
---> ed0db2759ed1
Successfully built ed0db2759ed1
Successfully tagged mycentos02:1.3

[root@Docker ~]# docker images mycentos02
REPOSITORY TAG IMAGE ID CREATED SIZE
mycentos02 1.3 ed0db2759ed1 About a minute ago 243MB

[root@Docker ~]# docker run -it --name test_c mycentos02:1.3
~
百度一下,你就知道
~

[root@Docker ~]# curl -k https://www.baidu.com -i
HTTP/1.1 200 OK
Accept-Ranges: bytes
Cache-Control: private, no-cache, no-store, proxy-revalidate, no-transform
Connection: keep-alive
Content-Length: 2443
Content-Type: text/html
Date: Thu, 11 Mar 2021 07:26:27 GMT
Etag: "588603eb-98b"
Last-Modified: Mon, 23 Jan 2017 13:23:55 GMT
Pragma: no-cache
Server: bfe/1.0.8.18
Set-Cookie: BDORZ=27315; max-age=86400; domain=.baidu.com; path=/

[root@Docker ~]# docker run -it --name test_c mycentos02:1.3 -i

[root@Docker ~]# docker run -it --name test_c mycentos02:1.3 -i
docker: Error response from daemon: Conflict. The container name "/test_c" is already in use by container "fdcf5c5e28df2f7d1dfde3c92903d808fc2b568966162d5594db1c7d1c6bf62a". You have to remove (or rename) that container to be able to reuse that name.
See 'docker run --help'.

此处产生报错原因:Docker中可以存在多个CMD命令,但是只有最后一个生效,CMD会被Docker run之后的参数替换,此处加入参数 -i,实际上是执行了代码命令 CMD -i,因此输出报错;

[root@Docker ~]# vim /myDocker/DockerFile_test02 
FROM centos
RUN yum install -y curl
ENTRYPOINT curl -k https://www.baidu.com
[root@Docker ~]# docker build -f /myDocker/DockerFile_test03 -t mycentos03:1.3 .
[root@Docker ~]# docker run -it --name test_d mycentos03:1.3
~
百度一下,你就知道
~

[root@Docker ~]# docker run -it --name test_d mycentos02:1.3 -i
HTTP/1.1 200 OK
Accept-Ranges: bytes
Cache-Control: private, no-cache, no-store, proxy-revalidate, no-transform
Connection: keep-alive
Content-Length: 2443
Content-Type: text/html
Date: Fri, 12 Mar 2021 07:50:23 GMT
Etag: "588603eb-98b"
Last-Modified: Mon, 23 Jan 2017 13:23:55 GMT
Pragma: no-cache
Server: bfe/1.0.8.18
Set-Cookie: BDORZ=27315; max-age=86400; domain=.baidu.com; path=/
~
百度一下,你就知道
~


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