Use of Dockerfile

Introduction to Dockerfile

Dockerfile is a text file that contains instructions (Instruction), and each instruction builds a layer, so the content of each instruction describes how the layer should be constructed.

Basic knowledge

Each command is an uppercase reserved keyword
The execution sequence is executed from top to bottom. Each command is a layer
# Indicates a comment

Use Dockerfile common instructions

command	effect	Example
FROM	The basic mirror tells who the mirror's mother is	FROM ubuntu
MAINTAINER	Who wrote the name + email address of the mirror
RUN	What do you want the mirror to do
COPY	Copy files to the container
ADD	If the source path is http path ADD command can goAutomatic download Then copy to the specified path, if the copied file is tar.gz ADD willAutomatic decompression And delete the compressed package
WORKDIR	The working directory of the container is cd
VOLUME	Where to store data
EXPOSE	Expose the mirrored port
CMD	The command specified when the container is started can only take effect at the end and will be replaced
ENTRYPOINT	The command specified when the container is started, the command can be appended and it will be appended
ONBUILD	But build an inherited Dockerfile
ENV	Set environment variables when building the image

command	effect	Example
FROM imageName	Which image must start the customized Dockerfile based on	FROM tomcat 或者 FROM tomcat:8.5.32
WORKDIR The directory to switch	Switching the workspace can replace the cd command	WORKDIR /usr/local/tomcat can switch the current directory to the specified directory
RUN bash command	Execute a bash command	RUN echo "Hello World"> /usr/local/1.txt etc.
COPY file/container path of the context path	Copy files to the container	COPY index.js /usr/local/docker/test
ADD the file of the context path. Container path	Copy files to the container	If the source path is http path, the ADD command can be downloaded and copied to the specified path. If the copied file is tar.gz ADD will automatically decompress and delete
CMD command	Start the program in the mirror	CMD [“nginx”, “-g”, “daemon off;”]
EXPOSE port [port 2, port 3,...]	Expose the port mirrored in the Docker container	EXPOSE [80,8080] or EXPOSE 80
. . . and many more

Build image

docker build -f dockerfile名称 -t 镜像名称 .  
# -f 指定dockerfile文件名
# -t 构建的镜像名称
# . 上下文路径

Precautions

The difference between CMD and ENTRYPOINT

RUN command executes multiple commands

#正确用法
RUN buildDeps='gcc libc6-dev make' \
    && apt-get update \
    && apt-get install -y $buildDeps \
    && wget -O redis.tar.gz "http://download.redis.io/releases/redis-3.2.5.tar.gz" \
    && mkdir -p /usr/src/redis \
    && tar -xzf redis.tar.gz -C /usr/src/redis --strip-components=1 \
    && make -C /usr/src/redis \
    && make -C /usr/src/redis install \
    && rm -rf /var/lib/apt/lists/* 

#错误用法
FROM debian:jessie
RUN apt-get update
RUN apt-get install -y gcc libc6-dev make
RUN wget -O redis.tar.gz "http://download.redis.io/releases/redis-3.2.5.tar.gz"
RUN mkdir -p /usr/src/redis
RUN tar -xzf redis.tar.gz -C /usr/src/redis --strip-components=1
RUN make -C /usr/src/redis
RUN make -C /usr/src/redis install

Each instruction in the Dockerfile represents a layer, the same is true for RUN, and the above writing method creates a 7-layer image. This is completely meaningless, not only will increase the build time, but also increase the chance of error!

Note: Union FS has a maximum number of layers. For example, AUFS used to have a maximum of 42 layers, but now it cannot exceed 127 layers.

The correct way of writing is to concatenate the Dockerfile instructions with the \ symbol to wrap and use &&, so that the previous seven layers are converted into one layer.

Attached, the contextual explanation of the Docker custom image

If you pay attention, you will see docker buildthe last command a .. .It represents the current directory, but Dockerfilein the current directory, so many beginners think that this is the path specified in Dockerfilethe path, so understanding is actually inaccurate. If the command corresponding to the above format, you may find that this is in the specified context path . So what is context?

Like this command

docker build -t imageName .

When building a Dockerfile, the user will specify the path to build the image context. After the docker build - t name .command knows this path, all content under the path specified by the user will be packaged and uploaded to the Docker engine. In this way, after the Docker engine receives the context package, it will get all the files needed to build the image.
If Dockerfileso write in:

COPY ./package.json /app/

This is not to copy execution docker builddirectory where Dockerfile of command package.json, nor is it to copy Dockerfilethe directory under package.json, but replication context (context) under the directory package.json.

Publish your own mirror

Publish to DockerHub

# 先登录自己的账户
docker login -u yufire
# 输入密码
Password: 
# 提示你没有把将未加密地存储在/root/.docker/config.json中。
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store
# 登陆成功
Login Succeeded

docker push 镜像名:版本号

Use DockerFile to build your own Docker image Introduction and use of DockerFile