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This article mainly introduces the Docker image layering and dockerfile writing skills of the relevant knowledge, the content is detailed and easy to understand, simple and fast operation, with a certain reference value, I believe that everyone after reading this Docker image layering and dockerfile writing skills what the article will have a harvest, let's take a look.

Docker image layering

Hierarchical introduction

Each instruction in Dockerfile creates a new mirror layer

The mirror layer will be cached and reused

When the Dockerfile instruction is modified, the copied file changes, or the specified variable when building the image is different, the corresponding mirror layer cache will be invalidated.

After the mirror cache of a certain layer expires, the mirror layer cache behind it will fail.

The mirror layer is immutable, and if you add a file to one layer and then delete it in the next layer, the file will still be included in the mirror

Docker mirroring principle

Docker images are superimposed by special file systems

The bottom end is bootfs, and the host bootfs is used.

The second layer is the root file system rootfs, called base image

Then other image files can be superimposed on it.

Unified File system (Union File System) technology can integrate different layers into a file system, providing a unified perspective for these layers, thus hiding the existence of multiple layers, from the user's point of view, there is only one file system.

One image can be placed on top of another. The mirror located below is called the parent mirror, and the bottom mirror becomes the base mirror.

When the container is launched from an image, Docker loads a read-write file system as the container at the top level.

1.base image: basic image

2.image: solidifies a standard operating environment, the function of the image itself-encapsulates a set of functional files, through a unified way, the file format is provided (read-only)

3.container: container layer (read / write)

4.docker-server end

5. Present to docker-client (View)

Mirror layered model

Dockerfile writing

Dockerfile operation instruction

The serial number instruction means that the 1FROM mirror specifies the mirror on which the new image is based. Article refers to the from instruction. Every time you create an image, you need a from instruction 2MAINTAINER name indicating the maintainer information of the new image. The 3RUN command executes the command on the image on which it is based and submits it to the new image. Each command executed in docker is the command or script to be run at the beginning of run 4CMD ["Program to run", "Parameter 1", "Parameter 2"] instruction to start the container. Dockerfile can only have one CMD command. If multiple commands are specified, only the last one can be executed by the 5EXPOSE port number to specify the port 6ENV environment variable value to be opened when the new image is loaded into Docker. Set the value of an environment variable. The compressed format is identified and decompressed automatically by the later run using 7ADD source files, directory target files / directories, and the source files are copied to the target files. The source files are located in the same directory as dockerfile, or a URL8COPY source file / directory destination file / directory copies the files / directories on the local host to the destination location. The source file / directory should be in the same directory as Dockerfile 9VOLUME ["directory"] create a mount point in the container 10USER username / UID specify the user 11WORKDIR path when running the container specify the subsequent RUN, CMD, ENTRYPOINT specify the working directory 12ONBUILD command to specify the generated image as a basic image the command 13HEALTHCHECK health check the difference between ADD and copy

Both the COPY instruction and the ADD instruction in ① Dockerfile can copy or add resources on the host to the container image, both of which are completed in the process of building the image.

② copy can only be used for replication (saving resources)

While ③ ADD replicates, ADD can also extract (consume resources) if the copied object is compressed.

The only difference between the ④ COPY directive and the ADD directive is whether it supports fetching resources from a remote URL. The COPY instruction can only read resources from the host on which the docker build is executed and copy them to the mirror. The ADD directive also supports reading resources from a remote server through URL and copying them to the mirror.

When ⑤ meets the same function, the COPY instruction is recommended. The ADD instruction is better at reading local tar files and extracting them.

The difference between CMD and entrypoint

Generally speaking, the square brackets of entrypoint will be used as the default execution command after the docker container is started, and the invariable parts are put in it. For example, the command parameters can be provided by default in the form of cmd, that is, the default parameters used when there are no parameters in run. If we want to use the default parameters, just run, otherwise if we want to use other parameters, add parameters to the run.

Try to write a dockerfile file to deploy nginx

Mkdir nginxcd nginx/vim Dockerfile FROM centos:7 # based on the basic image MAINTAINER nginx # user information RUN yum-y update # installation dependency RUN yum install-y pcre-devel zlib-devel gcc gcc-c++ makeRUN useradd-M-s / sbin/nologin nginx # create user ADD nginx-1.12.0.tar.gz / usr/local/src # copy the source file to the destination file Source files should be located in the same directory as Dockerfile Or a URL VOLUME ["/ usr/local/nginx/html"] # create a mount point in the container WORKDIR / usr/local/src # specify the working directory WORKDIR nginx-1.12.0RUN. / configure\-- prefix= / usr/local/nginx\-user=nginx\-group=nginx\-with-http_stub_status_module & & make & & make installENV PATH / usr/local/nginx/sbin:$PATHEXPOSE 80 # expose port RUN echo "demon off "> > / usr/local/nginx/conf/nginx.confCMD nginxdocker Why should I use daemon off to run nginx

Why should docker use daemon off to run nginx

This is the end of the article on "Docker image layering and dockerfile writing skills". Thank you for reading! I believe you all have a certain understanding of the knowledge of "Docker image layering and dockerfile writing skills". If you want to learn more, you are welcome to follow the industry information channel.

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