Dockerfile与Dockerfile实战

前言

​先前我们在讲述docker的镜像构建时对Dockerfile做了初步介绍,本文将结合上次的内容做更加细致的介绍,从回顾到实战演练讲述Dockerfile,本文先通过三个简单的案例感受、理解Dockerfile,主要是写httpd、sshd、以及systemctl的Dockerfile,之后会进行对其他服务如Nginx、Tomcat以及CentOS
#维护镜像的用户信息
MAINTAINER lokott@lokott.org
#镜像操作指令安装Apache软件
RUN yum -y update
RUN yum -y install httpd
#开启 80端口
EXPOSE 80
#复制网站首页文件
ADD index.html /var/www/html/index.html
#将执行脚本复制到镜像中
ADD run.sh /run.sh
RUN chmod 755 /run.sh
#启动容器是执行脚本
CMD [“/run.sh”]

其中注意:run 命令可以有多条CMD只能有一条,若有多条则只会执行最后一条

编写启动httpd服务的shell脚本

vim run.sh

#!/bin/bash
rm -rf /run/httpd/*
exec /usr/sbin/apachectl -D FOREGROUND

编写测试页面

vim index.html

<h1>this is docker httpd web</h1>

使用tree命令查看目录的文件结构

[root@localhost apache]# tree ./
./
├── Dockerfile
├── index.html
└── run.sh

0 directories, 3 files

构建和使用镜像(创建运行容器)

[root@localhost apache]# docker build -t httpd:new .
#因为我之前已经构建过,所以很快,此处案例显示过程是为了体现Dockerfile执行时的特征:分层和中间容器及镜像
Sending build context to Docker daemon  4.096kB
Step 1/9 : FROM centos:7
 ---> 5e35e350aded
Step 2/9 : MAINTAINER lokott@123.com
 ---> Using cache
 ---> 3a68b2812314
Step 3/9 : RUN yum -y update
 ---> Using cache
 ---> ecf1ecb0a774
Step 4/9 : RUN yum install -y httpd
 ---> Using cache
 ---> ae8c1ee32fbd
Step 5/9 : EXPOSE 80
 ---> Using cache
 ---> 29f12f1f7490
Step 6/9 : ADD index.html /var/www/html/index.html
 ---> Using cache
 ---> f56113e6b984
Step 7/9 : ADD run.sh /run.sh
 ---> Using cache
 ---> 886bf9e654ab
Step 8/9 : RUN chmod +x /run.sh
 ---> Using cache
 ---> bf53e19ad44f
Step 9/9 : CMD ["/run.sh"]
 ---> Using cache
 ---> 9500f0aefd1d
Successfully built 9500f0aefd1d
Successfully tagged httpd:new

[root@localhost apache]# docker images
REPOSITORY            TAG                 IMAGE ID            CREATED             SIZE
httpd                 new                 9500f0aefd1d        35 seconds ago      524MB
centos                7                   5e35e350aded        5 months ago        203MB
...//之后的案例将不再查看镜像了哈!
#基于构建的镜像创建并运行容器,给容器取名为test
[root@localhost apache]# docker run --name test -d -P httpd:new  
b7ec122849c61e36adb4a8891a87126afb53b1d5edfa2fda2a1ea18afa1a3169
[root@localhost apache]# docker ps -a
CONTAINER ID        IMAGE                 COMMAND                  CREATED             STATUS                      PORTS                   NAMES
b7ec122849c6        httpd:new             "/run.sh"                3 seconds ago       Up 3 seconds                0.0.0.0:32768->80/tcp   test

这样我们进入容器中检查一下这个页面文件是否存在

[root@localhost apache]# docker exec -it test /bin/bash
[root@b7ec122849c6 /]# cat /var/www/html/index.html 
<h1>this is docker httpd web</h1>

那么此时我们可以通过浏览器访问宿主机ip地址结合端口号(32768)来访问网站,结果如下:

Dockerfile与Dockerfile实战

下面的案例构建就直接给出Dockerfile和构建测试命令了。主要介绍其中的关键点。

2、构建sshd镜像

mkdir sshd 

cd sshd
#sshd服务的镜像构建——基于Dockerfile
#首先先下载基础镜像centos,创建对应的工作目录
#开始编写nginx的Dockerfile
#第一步:基础镜像
FROM centos:7
#第二步:维护者信息
MAINTAINER lokott@123.com
#第三步:指令集
RUN yum -y update
RUN yum -y install openssh* net-tools lsof telnet passwd 
RUN echo '123123' | passwd --stdin root
#不以PAM认证登录而是以密钥对登录(非对称密钥),即禁用ssh的PAM认证
RUN sed -i 's/UsePAM yes/UsePAM no/g' /etc/ssh/sshd_config
RUN ssh-keygen -t rsa -f /etc/ssh/ssh_host_rsa_key
#禁用ssh中PAM会话模块
RUN sed -i '/^session\s\+required\s\+pam_loginuid.so/s/^/#/' /etc/pam.d/sshd
#创建ssh工作目录和权限设置
RUN mkdir -p /root/.ssh && chown root:root /root && chmod 700 /root/.ssh
#开放22端口
EXPOSE 22
#第四步:启动容器时执行指令
CMD ["/usr/sbin/sshd","-D"]

构建镜像和运行容器

[root@localhost sshd]# docker build -t sshd:new .
[root@localhost sshd]# docker run -d -P sshd:new 
c7991648efebd192eb29f1d4e3503e47e0581f55381ff7a23e545041ef5d3e67
[root@localhost sshd]# docker ps -a
CONTAINER ID        IMAGE               COMMAND               CREATED             STATUS              PORTS                   NAMES
c7991648efeb        sshd:new            "/usr/sbin/sshd -D"   20 seconds ago      Up 20 seconds       0.0.0.0:32769->22/tcp   jolly_ishizaka
b7ec122849c6        httpd:new           "/run.sh"             20 minutes ago      Up 20 minutes       0.0.0.0:32768->80/tcp   test

测试

[root@localhost sshd]# ssh 20.0.0.149 -p 32769
The authenticity of host '[20.0.0.149]:32769 ([20.0.0.149]:32769)' can't be established.
RSA key fingerprint is SHA256:XLezVGFvOKIKW3fTBD0sIE9rsdz4021taphmcCo8IJM.
RSA key fingerprint is MD5:1e:86:94:2a:f5:a3:6c:e2:b4:b1:e4:50:9c:ad:8e:fb.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '[20.0.0.149]:32769' (RSA) to the list of known hosts.
root@20.0.0.149's password: 
[root@c7991648efeb ~]# exit
logout
Connection to 20.0.0.149 closed.

此时我们登录该容器(ssh或者docker exec命令)查看sshd服务的状态(但是systemctl无法使用)

[root@c7991648efeb ~]# systemctl status sshd
Failed to get D-Bus connection: Operation not permitted

一则我们可以使用下面的命令使用该命令,二则我们可以基于上面构建的镜像作为基础镜像构建systemctl的镜像来测试验证。

[root@localhost sshd]# docker run --privileged -itd -P sshd:new  /usr/sbin/init 
8dafa05dc12fc02f91dce93c6ab3085ab55eff1ee6b18c24731205e5c2ed37a9
[root@localhost sshd]# docker ps -a
CONTAINER ID        IMAGE               COMMAND               CREATED             STATUS              PORTS                   NAMES
8dafa05dc12f        sshd:new            "/usr/sbin/init"      3 seconds ago       Up 3 seconds        0.0.0.0:32770->22/tcp   hardcore_mccarthy
c7991648efeb        sshd:new            "/usr/sbin/sshd -D"   20 minutes ago      Up 20 minutes       0.0.0.0:32769->22/tcp   jolly_ishizaka
b7ec122849c6        httpd:new           "/run.sh"             40 minutes ago      Up 40 minutes       0.0.0.0:32768->80/tcp   test
[root@localhost sshd]# ssh 20.0.0.149 -p 32770
The authenticity of host '[20.0.0.149]:32770 ([20.0.0.149]:32770)' can't be established.
ECDSA key fingerprint is SHA256:LU81jNjOCKaiWrCsxTLPmx+YsUMVOBa2rG/XLXQsv9E.
ECDSA key fingerprint is MD5:03:15:aa:8a:65:8a:cc:b4:fb:66:f8:f6:6c:89:84:7b.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '[20.0.0.149]:32770' (ECDSA) to the list of known hosts.
root@20.0.0.149's password: 
[root@8dafa05dc12f ~]# systemctl status sshd
● sshd.service - OpenSSH server daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2020-04-22 02:28:49 UTC; 33s ago
     Docs: man:sshd(8)
           man:sshd_config(5)

–privileged表示提权,使得容器真正具备root的权限

3、构建systemctl镜像

mkdir systemctl
cd systemctl

创建Dockerfile

vim Dockerfile

FROM sshd:new
MAINTAINER lokott@123.com
ENV container docker
#下面的命令是放在一个镜像层中执行的,可以减少镜像层
#括号中的指令含义是遍历进入的目录文件,删除除了systemd-tmpfiles-setup.service的所有文件,之后删除一些其他文件
RUN (cd /lib/systemd/system/sysinit.target.wants/; for i in *; do [ $i == systemd-tmpfiles-setup.service ] || rm -f $i; done); \
rm -f /lib/systemd/system/multi-user.target.wants/*; \
rm -f /etc/systemd/system/*.wants/*; \
rm -f /lib/systemd/system/local-fs.target.wants/*; \
rm -f /lib/systemd/system/sockets.target.wants/*udev*; \
rm -f /lib/systemd/system/sockets.target.wants/*initctl*; \
rm -f /lib/systemd/system/basic.target.wants/*; \
rm -f /lib/systemd/system/anaconda.target.wants/*;
VOLUME [ "/sys/fs/cgroup" ]
CMD ["/usr/sbin/init"]

构建运行及测试

[root@localhost systemctl]# docker build -t systemctl:new .
[root@localhost systemctl]# docker run --privileged -it -v /sys/fs/cgroup/:/sys/fs/cgroup:ro systemctl:new /usr/sbin/init
systemd 219 running in system mode. (+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN)
Detected virtualization docker.
Detected architecture x86-64.

Welcome to CentOS Linux 7 (Core)!

Set hostname to <e99fd581042a>.
[  OK  ] Reached target Paths.
[  OK  ] Reached target Local File Systems.
[  OK  ] Reached target Swap.
[  OK  ] Created slice Root Slice.
[  OK  ] Listening on Journal Socket.
[  OK  ] Created slice System Slice.
         Starting Create Volatile Files and Directories...
[  OK  ] Listening on Delayed Shutdown Socket.
[  OK  ] Reached target Slices.
         Starting Journal Service...
[  OK  ] Started Create Volatile Files and Directories.
[ INFO ] Update UTMP about System Boot/Shutdown is not active.
[DEPEND] Dependency failed for Update UTMP about System Runlevel Changes.
Job systemd-update-utmp-runlevel.service/start failed with result 'dependency'.
[  OK  ] Started Journal Service.
[  OK  ] Reached target System Initialization.
[  OK  ] Started Daily Cleanup of Temporary Directories.
[  OK  ] Reached target Timers.
[  OK  ] Listening on D-Bus System Message Bus Socket.
[  OK  ] Reached target Sockets.
[  OK  ] Reached target Basic System.
[  OK  ] Reached target Multi-User System.

重新开启一个终端进行测试

[root@localhost systemctl]# docker ps -a
CONTAINER ID        IMAGE               COMMAND               CREATED              STATUS              PORTS                   NAMES
e99fd581042a        systemctl:new       "/usr/sbin/init"      About a minute ago   Up About a minute   22/tcp                  gifted_edison
8dafa05dc12f        sshd:new            "/usr/sbin/init"      6 minutes ago        Up 6 minutes        0.0.0.0:32770->22/tcp   hardcore_mccarthy
c7991648efeb        sshd:new            "/usr/sbin/sshd -D"   27 minutes ago       Up 27 minutes       0.0.0.0:32769->22/tcp   jolly_ishizaka
b7ec122849c6        httpd:new           "/run.sh"             46 minutes ago       Up 46 minutes       0.0.0.0:32768->80/tcp   test
[root@localhost systemctl]# docker exec -it gifted_edison /bin/bash
[root@e99fd581042a /]# systemctl status sshd
● sshd.service - OpenSSH server daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service; disabled; vendor preset: enabled)
   Active: inactive (dead)
     Docs: man:sshd(8)
           man:sshd_config(5)
[root@e99fd581042a /]# systemctl start sshd
[root@e99fd581042a /]# systemctl status sshd
● sshd.service - OpenSSH server daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service; disabled; vendor preset: enabled)
   Active: active (running) since Wed 2020-04-22 02:36:18 UTC; 1s ago
     Docs: man:sshd(8)
           man:sshd_config(5)
 Main PID: 51 (sshd)
   CGroup: /docker/e99fd581042af009c4a15e9ab7bdd231c0052056051a1b18e9996f57eb7f2c6b/system.slice/sshd.service
           └─51 /usr/sbin/sshd -D

Apr 22 02:36:18 e99fd581042a systemd[1]: Starting OpenSSH server daemon...
Apr 22 02:36:18 e99fd581042a sshd[51]: WARNING: 'UsePAM no' is not supported in Red Hat Enterprise Linux and may cause several problems.
Apr 22 02:36:18 e99fd581042a sshd[51]: Server listening on 0.0.0.0 port 22.
Apr 22 02:36:18 e99fd581042a sshd[51]: Server listening on :: port 22.
Apr 22 02:36:18 e99fd581042a systemd[1]: Started OpenSSH server daemon.
#开启sshd服务后进行访问宿主机测试成功
[root@e99fd581042a /]# ssh 20.0.0.149 -p 22
The authenticity of host '20.0.0.149 (20.0.0.149)' can't be established.
ECDSA key fingerprint is SHA256:pT/8N0H/tNaMm4Zqh7u28Jm5EtmDkidSaih4lWzFIQY.
ECDSA key fingerprint is MD5:16:47:40:1f:40:1b:34:e9:ff:f9:15:7b:0b:f4:02:8b.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '20.0.0.149' (ECDSA) to the list of known hosts.
root@20.0.0.149's password: 
Last login: Wed Apr 22 10:35:20 2020 from 20.0.0.149
[root@localhost ~]# exit
登出
Connection to 20.0.0.149 closed.
[root@e99fd581042a /]# exit
exit

总结

​ 本文回顾了Dockerfile,结合三个案例(httpd服务、sshd服务、systemd服务)来深入理解Dockerfile构建镜像的过程。其中我们需要理解的是

1、每个服务都需要有自己的目录和文件

2、Dockerfile的分层和中间缓存镜像和容器的创建和删除特点

3、–privileged的作用

4、体会整个从构建镜像、创建运行容器到测试验证的过程

谢谢阅读!

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