容器技术之Dockerfile(二)

2020-06-04 16:01:15来源:博客园 阅读 ()

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容器技术之Dockerfile(二)

用CMD或RUN指令运行命令时,如果直接在CMD或RUN指令后面接命令,这种方式通常会被解释为启动一个shell子进程运行命令,RUN指令表现形式就是后面的命令可以使用shell特性的语法格式的命令,比如大括号展开等等;而CMD指令表现形式就是启动为容器后,它默认会把我们指定运行的命令当作参数传给“/bin/sh”来运行;CMD或RUN指令加中括号的形式就表示使用json数组格式方式运行命令;这种方式运行命令在CMD中表现形式是我们运行的命令的选项都要当作参数传给该命令;RUN指令表现形式是不能使用shell特性的命令;如果非要使用shell特性的命令格式,我们需要把我们的命令当作参数传给“/bin/sh”,当然前提是我们的基础镜像shell支持shell特性的语法;

  前文我们聊到了什么是dockerfile,它的主要作用以及dockerfile的一些基本指令的使用方法,回顾请参考https://www.cnblogs.com/qiuhom-1874/p/13019411.html;今天我们在来聊一聊dockerfile余下指令的用法和作用;

  1、RUN:该指令用于docker build 过程中运行的程序,可以是任何命令;语法格式RUN <command> 或RUN ["<executable>", "<param1>", "<param2>"];第一种格式中,<command>通常是一个shell命令,且以“/bin/sh -c”来运行它,这意味着此进程在容器中的PID不为1,不能接收Unix信号,因此,当使用docker stop <container>命令停止容器时,此进程接收不到SIGTERM信号; 第二种语法格式中的参数是一个JSON格式的数组,其中<executable>为要运行的命令,后面的<paramN>为传递给命令的选项或参数;然而,此种格式指定的命令不会以“/bin/sh -c”来发起,因此常见的shell操作如变量替换以及通配符(?,*等)替换将不会进行;不过,如果要运行的命令依赖于此shell特性的话,可以将其替换为 RUN ["/bin/sh", "-c", "<executable>", "<param1>"]这样的格式;注意:json数组中,要使用双引号;

  示例:

[root@node1 test]# cat Dockerfile 
FROM centos:7 

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

ARG web_home

COPY html ${web_home:-"/data/htdoc/"}

VOLUME ${web_home:-"/data/htdoc/"}

EXPOSE 80/tcp 443/tcp

RUN mkdir -p /aaa/bbb/t{1..4}



[root@node1 test]# 

  提示:以上Dockerfile中,用RUN指令运行了mkdir命令,这种运行命令的方式在就可以利用shell的特性,如上大括号展开功能;

  验证:build 该dockerfile后,运行该镜像为容器,看看容器内部是否创建了/aaa/bbb/t1 t2 t3 t4?

[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
busybox             latest              1c35c4412082        16 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker build . -t myimg:v1
Sending build context to Docker daemon   1.05MB
Step 1/9 : FROM centos:7
 ---> b5b4d78bc90c
Step 2/9 : MAINTAINER "qiuhom <qiuhom@linux-1874.com>"
 ---> Running in 64c792ce6750
Removing intermediate container 64c792ce6750
 ---> 604899ef29f9
Step 3/9 : LABEL version="1.0"
 ---> Running in 6a3f9b4a9058
Removing intermediate container 6a3f9b4a9058
 ---> d9edea71fa22
Step 4/9 : LABEL description="this is test file \ that label-values can span multiple lines."
 ---> Running in b191ab5e19f9
Removing intermediate container b191ab5e19f9
 ---> ee027bbdc04b
Step 5/9 : ARG web_home
 ---> Running in a4c86febf616
Removing intermediate container a4c86febf616
 ---> 5b25bb7421dd
Step 6/9 : COPY html ${web_home:-"/data/htdoc/"}
 ---> 7c7a667149fa
Step 7/9 : VOLUME ${web_home:-"/data/htdoc/"}
 ---> Running in f9ec02d8f736
Removing intermediate container f9ec02d8f736
 ---> 86c7226f6b21
Step 8/9 : EXPOSE 80/tcp 443/tcp
 ---> Running in ad82d389ac25
Removing intermediate container ad82d389ac25
 ---> 28dadea40aff
Step 9/9 : RUN mkdir -p /aaa/bbb/t{1..4}
 ---> Running in 1013a212d3f2
Removing intermediate container 1013a212d3f2
 ---> 7f109a34a4a5
Successfully built 7f109a34a4a5
Successfully tagged myimg:v1
[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myimg               v1                  7f109a34a4a5        4 seconds ago       203MB
busybox             latest              1c35c4412082        16 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker run --name test --rm -it myimg:v1 /bin/bash
[root@fc89ca934ed5 /]# ls /
aaa                bin   dev  home  lib64  mnt  proc  run   srv  tmp  var
anaconda-post.log  data  etc  lib   media  opt  root  sbin  sys  usr
[root@fc89ca934ed5 /]# ls /aaa/
bbb
[root@fc89ca934ed5 /]# ls /aaa/bbb/
t1  t2  t3  t4
[root@fc89ca934ed5 /]# exit
exit
[root@node1 test]# 

  提示:底层基础镜像的shell如果不支持大括号展开,那么我们基于这种镜像做出来的镜像运行以上命令也就不支持shell的大括号展开功能;

  示例:

[root@node1 test]# cat Dockerfile
FROM centos:7

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

ARG web_home

COPY html ${web_home:-"/data/htdoc/"}

VOLUME ${web_home:-"/data/htdoc/"}

EXPOSE 80/tcp 443/tcp

RUN mkdir -p /aaa/bbb/t{1..4}

RUN ["mkdir","-p","/ccc/ddd/f{1..4}"]

[root@node1 test]# 

  提示:以json数组格式的方式去运行命令,它默认是不支持shell的任何特性,这意味着运行该命令时,不是基于shell子进程的方式在执行命令,通常是内核直接执行了;所以上面的命令它会把大括号处理成字符,而不会展开;

  验证:build成镜像运行成容器,看看是否把大括号处理成字符了?

[root@node1 test]# docker build . -t myimg:v1.1
Sending build context to Docker daemon   1.05MB
Step 1/10 : FROM centos:7
 ---> b5b4d78bc90c
Step 2/10 : MAINTAINER "qiuhom <qiuhom@linux-1874.com>"
 ---> Using cache
 ---> 604899ef29f9
Step 3/10 : LABEL version="1.0"
 ---> Using cache
 ---> d9edea71fa22
Step 4/10 : LABEL description="this is test file \ that label-values can span multiple lines."
 ---> Using cache
 ---> ee027bbdc04b
Step 5/10 : ARG web_home
 ---> Using cache
 ---> 5b25bb7421dd
Step 6/10 : COPY html ${web_home:-"/data/htdoc/"}
 ---> Using cache
 ---> 7c7a667149fa
Step 7/10 : VOLUME ${web_home:-"/data/htdoc/"}
 ---> Using cache
 ---> 86c7226f6b21
Step 8/10 : EXPOSE 80/tcp 443/tcp
 ---> Using cache
 ---> 28dadea40aff
Step 9/10 : RUN mkdir -p /aaa/bbb/t{1..4}
 ---> Using cache
 ---> 7f109a34a4a5
Step 10/10 : RUN ["mkdir","-p","/ccc/ddd/f{1..4}"]
 ---> Running in 9da1e6bab59f
Removing intermediate container 9da1e6bab59f
 ---> ae463ec8cbd9
Successfully built ae463ec8cbd9
Successfully tagged myimg:v1.1
[root@node1 test]# docker run --name test --rm -it myimg:v1.1 /bin/bash
[root@02ec6e404100 /]# ls /
aaa                bin  data  etc   lib    media  opt   root  sbin  sys  usr
anaconda-post.log  ccc  dev   home  lib64  mnt    proc  run   srv   tmp  var
[root@02ec6e404100 /]# ls /ccc/ddd/
f{1..4}
[root@02ec6e404100 /]# 

  提示:可以看到在/ccc/ddd/目录下并没有把大括号展开,而是直接把它当成了字符处理了;如果我们想要用json数组这种方式运行命令,又想让使用shell特性,我们可以使用"/bin/sh -c"来明确声明后面的命令用shell子进程的方式运行;如下所示

[root@node1 test]# cat Dockerfile
FROM centos:7

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

ARG web_home

COPY html ${web_home:-"/data/htdoc/"}

VOLUME ${web_home:-"/data/htdoc/"}

EXPOSE 80/tcp 443/tcp

RUN mkdir -p /aaa/bbb/t{1..4}

RUN ["/bin/bash","-c","mkdir -p /ccc/ddd/f{1..4}"]

[root@node1 test]# 

  提示:以上运行命令的方式就明确声明使用shell子进程的方式运行命令;这里需要注意一点的是,如果使用json数组的方式运行命令,后面真正执行的命令要一个整体当作参数传给"/bin/bash"

  验证:看看是否会把大括号展开?

[root@node1 test]# docker build . -t myimg:v1.2
Sending build context to Docker daemon   1.05MB
Step 1/10 : FROM centos:7
 ---> b5b4d78bc90c
Step 2/10 : MAINTAINER "qiuhom <qiuhom@linux-1874.com>"
 ---> Using cache
 ---> 604899ef29f9
Step 3/10 : LABEL version="1.0"
 ---> Using cache
 ---> d9edea71fa22
Step 4/10 : LABEL description="this is test file \ that label-values can span multiple lines."
 ---> Using cache
 ---> ee027bbdc04b
Step 5/10 : ARG web_home
 ---> Using cache
 ---> 5b25bb7421dd
Step 6/10 : COPY html ${web_home:-"/data/htdoc/"}
 ---> Using cache
 ---> 7c7a667149fa
Step 7/10 : VOLUME ${web_home:-"/data/htdoc/"}
 ---> Using cache
 ---> 86c7226f6b21
Step 8/10 : EXPOSE 80/tcp 443/tcp
 ---> Using cache
 ---> 28dadea40aff
Step 9/10 : RUN mkdir -p /aaa/bbb/t{1..4}
 ---> Using cache
 ---> 7f109a34a4a5
Step 10/10 : RUN ["/bin/bash","-c","mkdir -p /ccc/ddd/f{1..4}"]
 ---> Running in a5785a139e1f
Removing intermediate container a5785a139e1f
 ---> 30a5f5594104
Successfully built 30a5f5594104
Successfully tagged myimg:v1.2
[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myimg               v1.2                30a5f5594104        5 seconds ago       203MB
myimg               v1.1                ae463ec8cbd9        9 minutes ago       203MB
myimg               v1                  7f109a34a4a5        21 minutes ago      203MB
busybox             latest              1c35c4412082        16 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker run --name test --rm -it myimg:v1.2 /bin/bash
[root@549f875aa4de /]# ls /
aaa                bin  data  etc   lib    media  opt   root  sbin  sys  usr
anaconda-post.log  ccc  dev   home  lib64  mnt    proc  run   srv   tmp  var
[root@549f875aa4de /]# ls /ccc/ddd/
f1  f2  f3  f4
[root@549f875aa4de /]# 

  提示:可以看到用"/bin/bash -c" 是可以明确声明后面的命令用shell子进程的方式运行,这样一来就可以在后面的命令使用shell特性的语法;

  2、CMD:该指令类似于RUN指令,CMD指令也可用于运行任何命令或应用程序,不过,二者的运行时间点不同; RUN指令运行于映像文件构建过程中,而CMD指令运行于基于Dockerfile构建出的新映像文件启动一个容器时; CMD指令的首要目的在于为启动的容器指定默认要运行的程序,且其运行结束后,容器也将终止;不过,CMD指定的命令其可以被docker run的命令行选项所覆盖;在Dockerfile中可以存在多个CMD指令,但仅最后一个会生效;语法格式 CMD <command> 或 CMD [“<executable>”, “<param1>”, “<param2>”] 或 CMD ["<param1>","<param2>"];前两种语法格式的意义同RUN,第三种则用于为ENTRYPOINT指令提供默认参数;

  示例:

[root@node1 test]# cat Dockerfile
FROM busybox:latest

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

ARG web_home

COPY html ${web_home:-"/data/htdoc/"}

VOLUME ${web_home:-"/data/htdoc/"}

EXPOSE 80/tcp 443/tcp

CMD httpd -f -h /data/htdoc/
[root@node1 test]# 

  提示:docker容器内部运行的程序必须运行为前台;CMD是指定容器运行时要运行的命令;通常该命令或程序是以前台方式运行;如果不是前台运行,我们的容器就会存在一启动就退出的情况;以上命令就表示前台运行httpd程序 并指定httpd 的工作目录为${web_home}变量所指定的目录;

  验证:build后看看启动为容器是否提供80访问服务?

[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myimg               v1.2                30a5f5594104        23 minutes ago      203MB
myimg               v1.1                ae463ec8cbd9        32 minutes ago      203MB
myimg               v1                  7f109a34a4a5        44 minutes ago      203MB
busybox             latest              1c35c4412082        16 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker build . -t myimg:v1.3
Sending build context to Docker daemon   1.05MB
Step 1/9 : FROM busybox:latest
 ---> 1c35c4412082
Step 2/9 : MAINTAINER "qiuhom <qiuhom@linux-1874.com>"
 ---> Running in deb5e54eef87
Removing intermediate container deb5e54eef87
 ---> baf170e0c586
Step 3/9 : LABEL version="1.0"
 ---> Running in 433669185e0d
Removing intermediate container 433669185e0d
 ---> d96fb4ae3d58
Step 4/9 : LABEL description="this is test file \ that label-values can span multiple lines."
 ---> Running in b5da74e27c69
Removing intermediate container b5da74e27c69
 ---> 62372d19daf3
Step 5/9 : ARG web_home
 ---> Running in 3f65a67bb15a
Removing intermediate container 3f65a67bb15a
 ---> 1ce797c7cde0
Step 6/9 : COPY html ${web_home:-"/data/htdoc/"}
 ---> 15848dea21b9
Step 7/9 : VOLUME ${web_home:-"/data/htdoc/"}
 ---> Running in 868f4c10e00f
Removing intermediate container 868f4c10e00f
 ---> f3ec40d1cb5e
Step 8/9 : EXPOSE 80/tcp 443/tcp
 ---> Running in 7f72c2612e92
Removing intermediate container 7f72c2612e92
 ---> 5ccfc6d604cc
Step 9/9 : CMD httpd -f -h /data/htdoc/
 ---> Running in 95a4fd578821
Removing intermediate container 95a4fd578821
 ---> 2e296b4f4500
Successfully built 2e296b4f4500
Successfully tagged myimg:v1.3
[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myimg               v1.3                2e296b4f4500        3 seconds ago       1.22MB
myimg               v1.2                30a5f5594104        23 minutes ago      203MB
myimg               v1.1                ae463ec8cbd9        33 minutes ago      203MB
myimg               v1                  7f109a34a4a5        44 minutes ago      203MB
busybox             latest              1c35c4412082        16 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker run --name b1 -d myimg:v1.3
c3514f782cffd8140aa7c612293029f4d0302e8d697887dfc2696eea44a31700
[root@node1 test]# docker ps 
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
c3514f782cff        myimg:v1.3          "/bin/sh -c 'httpd -…"   4 seconds ago       Up 3 seconds        80/tcp, 443/tcp     b1
[root@node1 test]# curl http://172.17.0.2/test1.html
this is test1 html
[root@node1 test]# 

  提示:可以看到httpd是可以正常提供服务的;从上面的信息我们也可以了解到运行容器后,它默认是把我们写的命令当作shell子命令的方式在运行;

  示例:以json数组方式运行命令

[root@node1 test]# cat Dockerfile 
FROM busybox:latest

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

ARG web_home

COPY html ${web_home:-"/data/htdoc/"}

VOLUME ${web_home:-"/data/htdoc/"}

EXPOSE 80/tcp 443/tcp

CMD ["httpd","-f","-h","/data/htdoc/"]

[root@node1 test]# 

  提示:用json数组格式运行命令,需要把后面的每个选项当作参数传给httpd;

  验证:运行容器看看容器是否退出,是否能够正常提供httpd服务?

[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myimg               v1.3                2e296b4f4500        24 minutes ago      1.22MB
myimg               v1.2                30a5f5594104        47 minutes ago      203MB
myimg               v1.1                ae463ec8cbd9        57 minutes ago      203MB
myimg               v1                  7f109a34a4a5        About an hour ago   203MB
busybox             latest              1c35c4412082        17 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker build . -t myimg:v1.4
Sending build context to Docker daemon   1.05MB
Step 1/9 : FROM busybox:latest
 ---> 1c35c4412082
Step 2/9 : MAINTAINER "qiuhom <qiuhom@linux-1874.com>"
 ---> Using cache
 ---> baf170e0c586
Step 3/9 : LABEL version="1.0"
 ---> Using cache
 ---> d96fb4ae3d58
Step 4/9 : LABEL description="this is test file \ that label-values can span multiple lines."
 ---> Using cache
 ---> 62372d19daf3
Step 5/9 : ARG web_home
 ---> Using cache
 ---> 1ce797c7cde0
Step 6/9 : COPY html ${web_home:-"/data/htdoc/"}
 ---> Using cache
 ---> 15848dea21b9
Step 7/9 : VOLUME ${web_home:-"/data/htdoc/"}
 ---> Using cache
 ---> f3ec40d1cb5e
Step 8/9 : EXPOSE 80/tcp 443/tcp
 ---> Using cache
 ---> 5ccfc6d604cc
Step 9/9 : CMD ["httpd","-f","-h","/data/htdoc/"]
 ---> Running in 5bebdabfe2b7
Removing intermediate container 5bebdabfe2b7
 ---> 58e3b4c40ae7
Successfully built 58e3b4c40ae7
Successfully tagged myimg:v1.4
[root@node1 test]# docker run --name b1 -d myimg:v1.4
a32a05033a6dcb735363906bfcd2b84cfb290ca1b60c17d3ac2f81cdeceee705
[root@node1 test]# docker ps 
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
a32a05033a6d        myimg:v1.4          "httpd -f -h /data/h…"   6 seconds ago       Up 5 seconds        80/tcp, 443/tcp     b1
[root@node1 test]# curl http://172.17.0.2/test1.html
this is test1 html
[root@node1 test]# 

  提示:可以看到httpd服务可以正常提供访问,说明我们用json数组方式运行命令是正确的;总结一点,用CMD或RUN指令运行命令时,如果直接在CMD或RUN指令后面接命令,这种方式通常会被解释为启动一个shell子进程运行命令,RUN指令表现形式就是后面的命令可以使用shell特性的语法格式的命令,比如大括号展开等等;而CMD指令表现形式就是启动为容器后,它默认会把我们指定运行的命令当作参数传给“/bin/sh”来运行;CMD或RUN指令加中括号的形式就表示使用json数组格式方式运行命令;这种方式运行命令在CMD中表现形式是我们运行的命令的选项都要当作参数传给该命令;RUN指令表现形式是不能使用shell特性的命令;如果非要使用shell特性的命令格式,我们需要把我们的命令当作参数传给“/bin/sh”,当然前提是我们的基础镜像shell支持shell特性的语法;

  3、ENTRYPOINT:该指令类似CMD指令的功能,用于为容器指定默认运行程序,从而使得容器像是一个单独的可执行程序;与CMD不同的是,由ENTRYPOINT启动的程序不会被docker run命令行指定的参数所覆盖,而且,这些命令行参数会被当作参数传递给ENTRYPOINT指定的程序(不过,docker run命令的--entrypoint选项的参数可覆盖ENTRYPOINT指令指定的程序);语法格式 ENTRYPOINT <command>或 ENTRYPOINT ["<executable>", "<param1>", "<param2>"];docker run命令传入的命令参数会覆盖CMD指令的内容并且附加到ENTRYPOINT命令最后做为其参数使用;Dockerfile文件中也可以存在多个ENTRYPOINT指令,但仅有最后一个会生效;

  示例:

[root@node1 test]# cat Dockerfile
FROM busybox:latest

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

ARG web_home

COPY html ${web_home:-"/data/htdoc/"}

VOLUME ${web_home:-"/data/htdoc/"}

EXPOSE 80/tcp 443/tcp

ENTRYPOINT httpd -f -h /data/htdoc/
[root@node1 test]# 

  提示:以上dockerfile中用ENTRYPOINT 来指定容器默认运行程序,它和CMD不同的是,CMD指定运行的命令,我们可以使用docker run 命令加要运行的的命令替代容器里默认运行的命令,而ENTRYPOINT指定的命令我们是不可随便替换的,如果要替换必须要使用--entrypoint选项来指定;

  验证:build成镜像,我们启动为容器直接运行/bin/sh 看看是否可行?

[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myimg               v1.4                58e3b4c40ae7        23 minutes ago      1.22MB
myimg               v1.3                2e296b4f4500        47 minutes ago      1.22MB
myimg               v1.2                30a5f5594104        About an hour ago   203MB
myimg               v1.1                ae463ec8cbd9        About an hour ago   203MB
myimg               v1                  7f109a34a4a5        2 hours ago         203MB
busybox             latest              1c35c4412082        17 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker build . -t myimg:v1.5
Sending build context to Docker daemon   1.05MB
Step 1/9 : FROM busybox:latest
 ---> 1c35c4412082
Step 2/9 : MAINTAINER "qiuhom <qiuhom@linux-1874.com>"
 ---> Using cache
 ---> baf170e0c586
Step 3/9 : LABEL version="1.0"
 ---> Using cache
 ---> d96fb4ae3d58
Step 4/9 : LABEL description="this is test file \ that label-values can span multiple lines."
 ---> Using cache
 ---> 62372d19daf3
Step 5/9 : ARG web_home
 ---> Using cache
 ---> 1ce797c7cde0
Step 6/9 : COPY html ${web_home:-"/data/htdoc/"}
 ---> Using cache
 ---> 15848dea21b9
Step 7/9 : VOLUME ${web_home:-"/data/htdoc/"}
 ---> Using cache
 ---> f3ec40d1cb5e
Step 8/9 : EXPOSE 80/tcp 443/tcp
 ---> Using cache
 ---> 5ccfc6d604cc
Step 9/9 : ENTRYPOINT httpd -f -h /data/htdoc/
 ---> Running in de274d68686c
Removing intermediate container de274d68686c
 ---> 5825c2ec655f
Successfully built 5825c2ec655f
Successfully tagged myimg:v1.5
[root@node1 test]# docker run --name b1 --rm -it myimg:v1.5 /bin/sh

  提示:运行以上命令后,不会给我们一个shell终端,也不报错;但是我们直接访问httpd服务是可以正常访问的;这意味我们用docker run 命令是不能替换我们用entrypoint指定指定的命令的;

  测试:用--entrypoint 选项来看看是否能够覆盖ENTRYPOINT指定所指定的命令程序?

[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myimg               v1.5                5825c2ec655f        12 minutes ago      1.22MB
myimg               v1.4                58e3b4c40ae7        35 minutes ago      1.22MB
myimg               v1.3                2e296b4f4500        About an hour ago   1.22MB
myimg               v1.2                30a5f5594104        About an hour ago   203MB
myimg               v1.1                ae463ec8cbd9        2 hours ago         203MB
myimg               v1                  7f109a34a4a5        2 hours ago         203MB
busybox             latest              1c35c4412082        17 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker run --name b1 --rm -it --entrypoint "/bin/sh" myimg:v1.5
/ # ls
bin   data  dev   etc   home  proc  root  sys   tmp   usr   var
/ # ps
PID   USER     TIME  COMMAND
    1 root      0:00 /bin/sh
    7 root      0:00 ps
/ # 

  提示:可以看到使用docker run 必须要加--entrypoint 选项才可以覆盖ENTRYPOINT指令指定的命令;

  示例:使用json数组格式来指定命令

[root@node1 test]# cat Dockerfile 
FROM busybox:latest

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

ARG web_home

COPY html ${web_home:-"/data/htdoc/"}

VOLUME ${web_home:-"/data/htdoc/"}

EXPOSE 80/tcp 443/tcp

ENTRYPOINT ["httpd","-f","-h","/data/htdoc/"]

[root@node1 test]# 

  提示:使用json数组格式来指定命令时,都需要将后面的选项和参数当作该命令的参数传进去;

  测试:使用docker run 直接加命令 看看是否能够覆盖ENTRYPOINT指令指定的命令?

  提示:可以看到我们直接使用命令是无法覆盖ENTRYPOINT指令说指定的命令;

  示例:

[root@node1 test]# cat Dockerfile 
FROM centos:7

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

RUN yum install -y httpd

EXPOSE 80/tcp 

ENTRYPOINT ["/usr/sbin/httpd","-DFOREGROUND"]

[root@node1 test]# 

  测试:用docker run 命令覆盖ENTRYPOINT指定的默认命令,看看是否可行?

[root@node1 test]# docker build . -t myimg:v1.7
Sending build context to Docker daemon  1.051MB
Step 1/7 : FROM centos:7
 ---> b5b4d78bc90c
Step 2/7 : MAINTAINER "qiuhom <qiuhom@linux-1874.com>"
 ---> Using cache
 ---> 604899ef29f9
Step 3/7 : LABEL version="1.0"
 ---> Using cache
 ---> d9edea71fa22
Step 4/7 : LABEL description="this is test file \ that label-values can span multiple lines."
 ---> Using cache
 ---> ee027bbdc04b
Step 5/7 : RUN yum install -y httpd
 ---> Running in 164240645e39
Loaded plugins: fastestmirror, ovl
Determining fastest mirrors
 * base: mirrors.aliyun.com
 * extras: mirrors.aliyun.com
 * updates: mirrors.aliyun.com
Resolving Dependencies
--> Running transaction check
---> Package httpd.x86_64 0:2.4.6-93.el7.centos will be installed
--> Processing Dependency: httpd-tools = 2.4.6-93.el7.centos for package: httpd-2.4.6-93.el7.centos.x86_64
--> Processing Dependency: system-logos >= 7.92.1-1 for package: httpd-2.4.6-93.el7.centos.x86_64
--> Processing Dependency: /etc/mime.types for package: httpd-2.4.6-93.el7.centos.x86_64
--> Processing Dependency: libaprutil-1.so.0()(64bit) for package: httpd-2.4.6-93.el7.centos.x86_64
--> Processing Dependency: libapr-1.so.0()(64bit) for package: httpd-2.4.6-93.el7.centos.x86_64
--> Running transaction check
---> Package apr.x86_64 0:1.4.8-5.el7 will be installed
---> Package apr-util.x86_64 0:1.5.2-6.el7 will be installed
---> Package centos-logos.noarch 0:70.0.6-3.el7.centos will be installed
---> Package httpd-tools.x86_64 0:2.4.6-93.el7.centos will be installed
---> Package mailcap.noarch 0:2.1.41-2.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
 Package             Arch          Version                    Repository   Size
================================================================================
Installing:
 httpd               x86_64        2.4.6-93.el7.centos        base        2.7 M
Installing for dependencies:
 apr                 x86_64        1.4.8-5.el7                base        103 k
 apr-util            x86_64        1.5.2-6.el7                base         92 k
 centos-logos        noarch        70.0.6-3.el7.centos        base         21 M
 httpd-tools         x86_64        2.4.6-93.el7.centos        base         92 k
 mailcap             noarch        2.1.41-2.el7               base         31 k

Transaction Summary
================================================================================
Install  1 Package (+5 Dependent packages)

Total download size: 24 M
Installed size: 32 M
Downloading packages:
warning: /var/cache/yum/x86_64/7/base/packages/apr-util-1.5.2-6.el7.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID f4a80eb5: NOKEY
Public key for apr-util-1.5.2-6.el7.x86_64.rpm is not installed
--------------------------------------------------------------------------------
Total                                              7.8 MB/s |  24 MB  00:03     
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
Importing GPG key 0xF4A80EB5:
 Userid     : "CentOS-7 Key (CentOS 7 Official Signing Key) <security@centos.org>"
 Fingerprint: 6341 ab27 53d7 8a78 a7c2 7bb1 24c6 a8a7 f4a8 0eb5
 Package    : centos-release-7-8.2003.0.el7.centos.x86_64 (@CentOS)
 From       : /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : apr-1.4.8-5.el7.x86_64                                       1/6 
  Installing : apr-util-1.5.2-6.el7.x86_64                                  2/6 
  Installing : httpd-tools-2.4.6-93.el7.centos.x86_64                       3/6 
  Installing : centos-logos-70.0.6-3.el7.centos.noarch                      4/6 
  Installing : mailcap-2.1.41-2.el7.noarch                                  5/6 
  Installing : httpd-2.4.6-93.el7.centos.x86_64                             6/6 
  Verifying  : mailcap-2.1.41-2.el7.noarch                                  1/6 
  Verifying  : apr-util-1.5.2-6.el7.x86_64                                  2/6 
  Verifying  : httpd-2.4.6-93.el7.centos.x86_64                             3/6 
  Verifying  : apr-1.4.8-5.el7.x86_64                                       4/6 
  Verifying  : httpd-tools-2.4.6-93.el7.centos.x86_64                       5/6 
  Verifying  : centos-logos-70.0.6-3.el7.centos.noarch                      6/6 

Installed:
  httpd.x86_64 0:2.4.6-93.el7.centos                                            

Dependency Installed:
  apr.x86_64 0:1.4.8-5.el7                                                      
  apr-util.x86_64 0:1.5.2-6.el7                                                 
  centos-logos.noarch 0:70.0.6-3.el7.centos                                     
  httpd-tools.x86_64 0:2.4.6-93.el7.centos                                      
  mailcap.noarch 0:2.1.41-2.el7                                                 

Complete!
Removing intermediate container 164240645e39
 ---> 63db91f4fe6a
Step 6/7 : EXPOSE 80/tcp
 ---> Running in 6585da71fc3b
Removing intermediate container 6585da71fc3b
 ---> eb671cf67f52
Step 7/7 : ENTRYPOINT ["/usr/sbin/httpd","-DFOREGROUND"]
 ---> Running in f6e7297025af
Removing intermediate container f6e7297025af
 ---> bac03b20761a
Successfully built bac03b20761a
Successfully tagged myimg:v1.7
[root@node1 test]# docker run --name m1 --rm -it myimg:v1.7 /bin/sh
Usage: /usr/sbin/httpd [-D name] [-d directory] [-f file]
                       [-C "directive"] [-c "directive"]
                       [-k start|restart|graceful|graceful-stop|stop]
                       [-v] [-V] [-h] [-l] [-L] [-t] [-T] [-S] [-X]
Options:
  -D name            : define a name for use in <IfDefine name> directives
  -d directory       : specify an alternate initial ServerRoot
  -f file            : specify an alternate ServerConfigFile
  -C "directive"     : process directive before reading config files
  -c "directive"     : process directive after reading config files
  -e level           : show startup errors of level (see LogLevel)
  -E file            : log startup errors to file
  -v                 : show version number
  -V                 : show compile settings
  -h                 : list available command line options (this page)
  -l                 : list compiled in modules
  -L                 : list available configuration directives
  -t -D DUMP_VHOSTS  : show parsed vhost settings
  -t -D DUMP_RUN_CFG : show parsed run settings
  -S                 : a synonym for -t -D DUMP_VHOSTS -D DUMP_RUN_CFG
  -t -D DUMP_MODULES : show all loaded modules 
  -M                 : a synonym for -t -D DUMP_MODULES
  -t                 : run syntax check for config files
  -T                 : start without DocumentRoot(s) check
  -X                 : debug mode (only one worker, do not detach)
[root@node1 test]# 

  提示:可以看到我们用docker run指定命令去覆盖ENTRYPOINT指令指定的命令,它给我们打印了httpd命令的用法,这说明我们后面传递的/bin/sh 当作参数传递给ENTRYPOINT说指定的命令;这里还需要说一下,上面的示例用docker run 去覆盖ENTRYPOINT指令指定的命令,没有报错的原因应该是busybox里的httpd程序支持传递/bin/sh当作参数;

  示例:CMD指令同ENTRYPOINT一起使用

[root@node1 test]# cat Dockerfile 
FROM centos:7

MAINTAINER "qiuhom <qiuhom@linux-1874.com>"

LABEL version="1.0"

LABEL description="this is test file \ that label-values can span multiple lines."

RUN yum install -y httpd

ADD entrypoint.sh /bin/

EXPOSE 80/tcp 

CMD ["/usr/sbin/httpd","-DFOREGROUND"]

ENTRYPOINT ["/bin/entrypoint.sh"]

[root@node1 test]# 

  提示:以上dockerfile使用了CMD和ENTRYPOINT指令来指定容器默认运行程序;此时CMD所指定的命令默认会以参数的形式传给ENTRYPOINT指令所指定的命令;而上面ENTRYPOINT指定指定的是一个脚本,也就说上面dockerfile最终运行的命令是/bin/entrypoint.sh /usr/sbin/httpd -DFOREGROUND;这里的脚本就相当于中间层,通过脚本设定一些参数,然后把CMD指定的命令当作参数传给脚本,最终脚本运行起来;

  entrypoint脚本

[root@node1 test]# ll
total 1032
-rw-r--r-- 1 root root     307 Jun  3 11:28 Dockerfile
-rwxr-xr-x 1 root root     300 Jun  3 11:22 entrypoint.sh
drwxr-xr-x 2 root root      42 May 31 01:51 html
-rw-r--r-- 1 root root 1043748 May 26 11:07 nginx-1.19.0.tar.gz
-rw-r--r-- 1 root root      22 May 31 01:52 test.html
[root@node1 test]# cat entrypoint.sh 
#!/bin/bash

doc_root=${DOC_ROOT:-/var/www/html}
cat > /etc/httpd/conf.d/myweb.conf <<EOF
        <virtualhost *:80>
                servername "localhost"
                documentroot "${doc_root}"
                <directory "${doc_root}">
                        options none
                        allowoverride none
                        require  all granted
                </directory>
        </virtualhost>
EOF

exec "$@"
[root@node1 test]# 

  提示:这个脚本很简单就是在/etc/httpd/conf.d/生成一个myweb.conf的配置文件,然后最后引用脚本的参数运行;exec "$@" 表示把脚本的所有参数独立运行成一个守护进程;默认不使用exec就表示以shell子进程的方式运行,exec就表示运行为单独的守护进程,不再是shell子进程的方式;

  测试:

[root@node1 test]# docker build . -t httpd:v1
Sending build context to Docker daemon  1.051MB
Step 1/9 : FROM centos:7
 ---> b5b4d78bc90c
Step 2/9 : MAINTAINER "qiuhom <qiuhom@linux-1874.com>"
 ---> Using cache
 ---> 604899ef29f9
Step 3/9 : LABEL version="1.0"
 ---> Using cache
 ---> d9edea71fa22
Step 4/9 : LABEL description="this is test file \ that label-values can span multiple lines."
 ---> Using cache
 ---> ee027bbdc04b
Step 5/9 : RUN yum install -y httpd
 ---> Using cache
 ---> 63db91f4fe6a
Step 6/9 : ADD entrypoint.sh /bin/
 ---> 49d1270c3aa3
Step 7/9 : EXPOSE 80/tcp
 ---> Running in 3dacf6acf23b
Removing intermediate container 3dacf6acf23b
 ---> edced77af5b5
Step 8/9 : CMD ["/usr/sbin/httpd","-DFOREGROUND"]
 ---> Running in 23bb32def296
Removing intermediate container 23bb32def296
 ---> 169a5e164ba5
Step 9/9 : ENTRYPOINT ["/bin/entrypoint.sh"]
 ---> Running in f3bf0c267c7b
Removing intermediate container f3bf0c267c7b
 ---> 0801db092665
Successfully built 0801db092665
Successfully tagged httpd:v1
[root@node1 test]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
httpd               v1                  0801db092665        35 seconds ago      307MB
myimg               v1.7                bac03b20761a        12 minutes ago      307MB
myimg               v1.6                5370df4238eb        2 hours ago         1.22MB
myimg               v1.5                5825c2ec655f        2 hours ago         1.22MB
myimg               v1.4                58e3b4c40ae7        2 hours ago         1.22MB
myimg               v1.3                2e296b4f4500        3 hours ago         1.22MB
myimg               v1.2                30a5f5594104        3 hours ago         203MB
myimg               v1.1                ae463ec8cbd9        3 hours ago         203MB
myimg               v1                  7f109a34a4a5        3 hours ago         203MB
busybox             latest              1c35c4412082        19 hours ago        1.22MB
centos              7                   b5b4d78bc90c        4 weeks ago         203MB
[root@node1 test]# docker run --name h1 -d httpd:v1
cee14b04912822c33e7deeee361e1ce0c20d7daf6c0666bff319bf3f1bc69bdc
[root@node1 test]# docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
cee14b049128        httpd:v1            "/bin/entrypoint.sh …"   9 seconds ago       Up 9 seconds        80/tcp              h1
[root@node1 test]# 

  提示:可以看到我们build成镜像后,直接运行为容器,容器正常;我们进入容器内部看看它到底运行的说明命令

[root@node1 test]# docker exec -it h1 /bin/bash
[root@cee14b049128 /]# ls /etc/httpd/conf.d/myweb.conf 
/etc/httpd/conf.d/myweb.conf
[root@cee14b049128 /]# cat /etc/httpd/conf.d/myweb.conf
        <virtualhost *:80>
                servername "localhost"
                documentroot "/var/www/html"
                <directory "/var/www/html">
                        options none
                        allowoverride none
                        require  all granted
                </directory>
        </virtualhost>
[root@cee14b049128 /]# ps aux
USER        PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root          1  0.0  0.1 224080  5016 ?        Ss   16:26   0:00 /usr/sbin/httpd -D
apache        7  0.0  0.0 224212  2960 ?        S    16:26   0:00 /usr/sbin/httpd -D
apache        8  0.0  0.0 224212  2960 ?        S    16:26   0:00 /usr/sbin/httpd -D
apache        9  0.0  0.0 224212  2960 ?        S    16:26   0:00 /usr/sbin/httpd -D
apache       10  0.0  0.0 224212  2960 ?        S    16:26   0:00 /usr/sbin/httpd -D
apache       11  0.0  0.0 224212  2960 ?        S    16:26   0:00 /usr/sbin/httpd -D
root         12  0.0  0.0  11828  1932 pts/0    Ss   16:35   0:00 /bin/bash
root         27  0.0  0.0  51756  1720 pts/0    R+   16:36   0:00 ps aux
[root@cee14b049128 /]# httpd -t -D DUMP_VHOSTS
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message
VirtualHost configuration:
*:80                   localhost (/etc/httpd/conf.d/myweb.conf:1)
[root@cee14b049128 /]# 

  提示:可以看到容器内部运行的就是/usr/sbin/httpd -DFOREGROUND这个命令;其实这个命令不是CMD直接运行的命令,而是通过脚本获取参数而来的;我们通过脚本添加的配置文件都在对应的位置,并且也都生效了;总结一点,通常CMD和ENTRYPOINT应用在通过entrypoint脚本做中间层向容器内运行的程序提供配置文件的场景,通常这些应用程序不是云原生的;


原文链接:https://www.cnblogs.com/qiuhom-1874/p/13040273.html
如有疑问请与原作者联系

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