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This article will explain the example analysis of Docker for you in detail. The editor thinks it is very practical, so I share it with you as a reference. I hope you can get something after reading this article.

What is Docker?

What is Docker?

Introduction to the home page of the official website:

Enterprise Container Platform for High-Velocity Innovation. Securely build, share and run any application, anywhere

Baidu encyclopedia tells us:

Docker is an open source application container engine that allows developers to package their applications and dependency packages into a portable container, then publish them to any popular Linux machine, or virtualize them. Containers are completely sandboxed and do not have any interface to each other.

A brief introduction to the first DOCKER Book:

Docker is an open source engine that automatically deploys developed applications to containers. Written by the team of Docker (www.docker.com, former dotCloud, an established supplier in the PaaS market) and released based on the Apache 2.0 open source protocol.

What makes Docker special:

Docker is a lightweight virtualization technology with fast startup speed (most Docker containers can be started in less than 1 second). Hundreds of containers can be run on a single hardware at the same time, making rapid expansion and auto scaling easy. It is said that in 2016, JD.com used 150000 Docker clusters to ensure system stability in high concurrency scenarios.

Docker is cross-platform and supports Windows, Macos and Linux. It can "build once, run everywhere" to solve a series of problems caused by the inconsistency between development environment and production environment, so that developers and operators can get along more harmoniously.

Docker is open source and hosted on GitHub.

Docker thought

From the core idea of logo Lenovo docker of docker

Docker's logo is a big whale carrying a container, which is definitely the most vivid description and explanation of Docker.

In contrast to the transport industry, before the advent of containers, goods could not be transported in a uniform standard way. for example, some goods are fragile and need to be handled lightly, while others do not. So railway, road, sea and other kinds of transport, need a lot of manpower as goods transfer, the efficiency is very low, and the cost is very high. After the emergence of the container, the problem was solved. Any goods can be put into this magical box, and then in all transportation scenarios such as roads, railways, oceans, and so on, the box is sealed in the course of transportation. and the transit work in the middle can be done by large machinery, and the efficiency is greatly improved.

Docker formally draws lessons from the idea of standard container and applies the idea of container to the field of software. Docker provides code with a standardized container-based transportation system that can package any application and its dependent environment (such as code, configuration files, JDK, Tomcat, etc.) into a container that can run on almost all operating systems.

Core concepts of Docker

Mirror image

Mirroring is the cornerstone of docker, based on which users can run their own containers.

Mirroring is based on Docker's federated file system, which is hierarchical and each mirror is a tier. Since there are other layers above each layer, that is, the mirror can be created on top of other mirrors (base images). Borrow a picture to help understand. The picture comes from the network, invades and deletes.

Warehouse

The repository is the place where user images are stored. The official docker repository address is https://hub.docker.com. There are many mirrors on Docker Hub, including the simplest hello-world,MySQL and so on. Of course, we can also have our own private warehouse.

Container

The container provides isolated running space for the application. Each container contains a unique and complete user environment, and changes in the running environment in one container will not affect the operating environment of other containers, allowing applications to run in the same way almost anywhere.

The container is started based on an image, and one or more processes can be run in the container. When creating a container process, you specify the Namespace parameters required by the process, so that the container can only "see" the resources, files, devices, states, or configurations defined by the current Namespace. Therefore, the container is just a special process, and the essence of the container is the process.

Docker installation

Take CentOS 7 as an example to install Docker.

Check the kernel version of the system

Docker runs on CentOS 7 and requires the operating system to be 64-bit and kernel version 3.10 or above.

Verify that the Linux kernel that meets the requirements is installed on this machine. Use the command uname-r to check the kernel version information.

[root@localhost] # uname-r3.10.0-957.el7.x86_64

Install Docker in CentOS 7

Use the command yum install-y docker to install Docker, "- y" means do not ask, install using the default configuration.

Start the Docker service and set it to boot

Use the following command:

Systemctl start docker.servicesystemctl enable docker.service

Enter docker version and return the version information to indicate that Docker is installed successfully.

[root@localhost] # docker versionClient: Version: 1.13.1 API version: 1.26 Package version: docker-1.13.1-96.gitb2f74b2.el7.centos.x86_64 Go version: go1.10.3 Git commit: b2f74b2/1.13.1 Built: Wed May 1 14:55:20 2019 OS/Arch: linux/amd64Server: Version: 1.13.1 API version: 1.26 (minimum version 1.12) Package version: docker- 1.13.1-96.gitb2f74b2.el7.centos.x86_64 Go version: go1.10.3 Git commit: b2f74b2/1.13.1 Built: Wed May 1 14:55:20 2019 OS/Arch: linux/amd64 Experimental: false

Docker actual combat-- Hello World

How can you get the classic "Hello World" without the entry-level actual combat?

Pull the image

In fact, this image is already available on DockerHub, which is called "hello-world". Pull the image directly from DockerHub. The command is similar to Git: docker pull hello-world

[root@localhost docker] # docker pull hello-worldUsing default tag: latestTrying to pull repository docker.io/library/hello-world... Latest: Pulling from docker.io/library/hello-world1b930d010525: Pull complete Digest: sha256:41a65640635299bab090f783209c1e3a3f11934cf7756b09cb2f1e02147c6ed8Status: Downloaded newer image for docker.io/hello-world:latest

View Mirror

Check the Docker image pulled: docker images

[root@localhost ~] # docker imagesREPOSITORY TAG IMAGE ID CREATED SIZEdocker.io/hello-world latest fce289e99eb9 5 months ago 1.84 kB

Run Mirror

Run the image: docker run hello-world. When you see the following content printed out, it indicates that the operation is successful.

[root@localhost docker] # docker run hello-worldHello from Docker!This message shows that your installation appears to be working correctly.To generate this message, Docker took the following steps: 1. The Docker client contacted the Docker daemon. 2. The Docker daemon pulled the "hello-world" image from the Docker Hub. (amd64) 3. The Docker daemon created a new container from that image which runs the executable that produces the output you are currently reading. 4. The Docker daemon streamed that output to the Docker client, which sent it to your terminal.To try something more ambitious, you can run an Ubuntu container with: $docker run-it ubuntu bashShare images, automate workflows, and more with a free Docker ID: https://hub.docker.com/For more examples and ideas, visit: https://docs.docker.com/get-started/

Docker common commands

Docker images: lists local images

Docker pull image_name: pull the image. If no specific image tag is specified, the image of the latest tag will be pulled automatically.

Docker search image_name: finding images on Docker Hub

Docker start container: start and run the container

Docker run [OPTIONS] image_name: create and start a container based on an image

Common options:

-d: runs the container in the background and returns the container ID

-I: runs the container in interactive mode, usually in conjunction with-t

-t: reassign a pseudo-input terminal to the container, usually used in conjunction with-I

-P: random port mapping, the container internal port is randomly mapped to the high port of the host

-p: specify port mapping. Format: host (host) port: container port

Docker logs container: get the log information of the container

Docker attach container: enter the container

Exit: exit the container

Docker exec container command: execute commands in the running container

Docker stop container: stop the container

Docker rm container: deleting containers

Docker save-o image_name.tar image_name: export image

Docker ps: view running containers

Docker ps-a: view the list of containers in the system

Docker top container: view the processes in the container

Docker stop daemon_dave: stop guarding the container

Docker builds an image

How to build an image?

It takes two steps to build your own image:

Write Dockerfile. Dockerfile tells Docker how to make a mirror and what each step is like.

The process by which Docker executes instructions in Dockerfile is as follows:

Docker runs a container from the base image

Execute an instruction to modify the container

Submit to a new mirror layer

Docker runs a new container based on the image just submitted

Execute the next instruction in Dockerfile until all instructions have been executed.

Build using the docker build command.

Write Dockerfile

The first command for each Dockerfile must be FROM. The FROM instruction specifies an existing image, telling Docker that subsequent instructions are based on this. For example: FROM java:8

The MAINTAINER directive is used to identify the owner and contact information of the image. For example: MAINTAINER James "× × @ example.com"

The VOLUME directive is used to add volumes to containers created based on mirrors. A volume can be a specific directory that exists in one or more containers that bypasses the federated file system and provides the ability to share data and persist data.

The CMD directive is used to specify a command to run when the container starts.

The ENTRYPOINT instruction is very similar to the CMD instruction.

When the WORKDIR directive is used to create a new container from the mirror, a working command is set inside the container, and the program specified by the ENTRYPOINT or CMD directive is executed in this directory.

The ENV directive is used to set environment variables during the image build process. For example: ENV TEST_PATH / home/test

The RUN directive is used to run the specified command in the current image. For example: RUN apt-get install-y nginx

The EXPOSE directive is used to tell Docker that the application in the container will use the specified port of the container. For example: EXPOSE 80

The ADD directive is used to copy files and directories from the build environment to the image. For example: ADD docker-0.0.1-SNAPSHOT.jar app.jar

The COPY directive is similar to ADD, except that COPY only cares about copying local files in the build context, not extracting and decompressing them.

The LABEL directive is used to add metadata to the Docker mirror. For example: LABEL name=test description= "a container is used to test"

Dockerfile instance:

FROM java:8MAINTAINER James "× × @ example.com" VOLUME / tmpADD docker-0.0.1-SNAPSHOT.jar app.jarENTRYPOINT ["java", "- Djava.security.egd=file:/dev/./urandom", "- jar", "/ app.jar"]

Execute docker build

Seeing "BUILD SUCCESS" after executing the docker build command indicates that the build is successful and can be run using the docker run command.

This is the end of this article on "sample Analysis of Docker". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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