How docker customizes images

How does docker customize the image?

1. To utilize docker technology, you must first install the docker package

This time I used docker-engine-1.12.1-1. el7.centos.x86_64.rpm; docker technology is based on the underlying system of the local machine. On top of the system, applications are packaged and delivered. It allows containers to be started as quickly as a process.
Based on docker technology, the required minimum system environments can be encapsulated as a mirror and started like a process.

2. Make a custom docker image
First download a docker image from the docker official website

docker search docker
docker pull docker

The images on the official website are all It is a minimal installation, so you must first configure a yum source, install the commonly used software in the centos image, and start httpd and sshd. The specific operations are as follows:

yum -y install docker-engine-1.12.1-1.el7.centos.x86_64.rpm
mkdir testcd testtouch Dockerfile
vim Dockerfile
FROM centos:latest
RUN rm -f /etc/yum.repos.d/*
ADD centos7.repo /etc/yum.repos.d/centos7.repo
RUN yum -y install httpd openssh-server net-tools bash-completion.noarch \ iproute vim-enhanced
EXPOSE 80 22
RUN  echo "123456" |passwd --stdin root
RUN  /usr/sbin/sshd-keygen
ENV EnvironmentFile=/etc/sysconfig/sshd
WORKDIR /var/www/html
RUN echo "<h1><font color=red>this is centos1:httpd">index.html
ENV EnvironmentFile=/etc/sysconfig/httpd
ADD qd.sh /root/qd.sh    
CMD ["/root/qd.sh"]
:wq

Note:
EXPOSE specifies which ports of the open container;
ADD transfers the files in the current directory to the specified directory in the container; it must be the current path
RUN refers to executing in the container Which commands;
FROM specifies the source image, that is, which image this image is based on.
WORKDIR is the working directory in the specified container, which is equivalent to the cd command in the centos system
ENV is to define the environment variable
CMD specifies the first command to be executed after the container is started. You need to use [] separated by quotes. If there are options, separate them with commas, for example: ["/usr/sbin/sshd", "-D"]
The file created must be called Dockerfile
If you feel like writing these commands manually, compare It's complicated. You can enter the basic image to execute various commands, then use history to view the commands, use the cp command, and replace it with the corresponding format above.

3. Write the startup script
Since the CMD of the docker image is the first default command to be executed after the container is started, you can only write in the CMD A command, and in this case, we want to start two programs sshd and httpd, so we need to write a script and let CMD execute the script directly.

vim qd.sh#!/bin/bash/usr/sbin/sshd -D &
/usr/sbin/httpd -DFOREGROUND
：wq

chmod x qd.sh //Add execution permissions
4. Create a mirror
Needs to be executed in the current directory

docker build -t wang:sh2 .

5. Start the image and map the port of the container.

docker run -d -p 80:80 -p 2022:22 wang:sh2

Map port 80 of the container to port 80 of the physical machine, and map port 22 of the container to the physical machine. Port 2022.
6. Access verification

firefox http://192.168.1.194(物理机)
ssh -p 2022 192.168.1.194

7. Extension
You can also make a mirror of the sshd service first, and then Make an httpd container based on the sshd image:

im Dockerfile
FROM wang:sshd
RUN yum -y  httpd
EXPOSE 80 22ENV EnvironmentFile=/etc/sysconfig/httpd
WORKDIR /var/www/html
RUN echo "<h1><font color=red>this is httpd and sshd">index.html
ADD qd.sh /root/qd.sh    
CMD ["/root/qd.sh"] 
:wq

Related references: docker tutorial

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