What exactly is docker and why is it so popular? What are its advantages and disadvantages?

What is Docker?

　To put it simply, Docker is a "container" (Linux containers, LXCs) that is run by a program written in the GO language; the cornerstone of current cloud services is operating system level isolation, which virtualizes multiple containers on the same physical server. host. Docker implements an application-level isolation; it changes our basic development and operation unit from directly operating the virtual host (VM) to a "container" where the operating program runs.

　Docker is an open platform designed for developers and system administrators to publish and run distributed applications. Composed of two parts:

　 Docker Engine: a portable, lightweight runtime environment and package manager. (Note* Single OS vs single thread, is it particularly similar to NodeJS?)

　Docker Hub: A cloud service created for creating automated workflows and sharing applications. (Note* Cloud image/package management vs npm package management, is it particularly similar to npm?)

From March 20, 2013, the first version of Docker was officially released to June 2014, when Docker 1.0 was officially released. Experience for 15 months. Although its development history is very short, Docker is becoming more and more popular.

In fact, Container technology is not an innovation of Docker. Cloud service providers such as HeroKu and NodeJitsu have adopted similar lightweight virtualization technology. However, Docker is the first to open source this Container technology on a large scale and is widely accepted by the community. of.

　The good part

　The advantages of Docker over VM virtual machines are very obvious, that is, lightweight, high performance and convenience. The following part is excerpted from: KVM and Docker LXC Benchmarking with OpenStack

　Fast

　Runtime Performance can be greatly improved (the classic case is an improvement of 97%)

Management operations (start, stop, start, restart, etc.) are all measured in seconds or milliseconds.

　 Agile

As agile as a virtual machine, and cheaper, deployment on bare metal is as easy as clicking a button.

　 Flexible

“Containerize” applications and systems without adding additional operating systems,

Lightweight

You will have enough “operating systems”, just add or reduce images. 100~1000 Containers containers can be deployed on a server.

　Cheap

　Open source, free and low-cost. Supported and driven by the modern Linux kernel. Note* Lightweight Container can certainly open more "containers" on a physical machine, and is destined to be cheaper than VMs.

　Ecosystems

　are becoming more and more popular, just look at Google Trends, docker or LXC.

　There are countless community and third-party applications.

　Cloud Support

　Countless cloud services provide frameworks for creating and managing Linux containers.

　 Regarding the performance advantages of Docker, you can also refer to this IBM engineer’s evaluation of performance improvement. It is greatly improved compared to VMs (OS system level virtualization) in all aspects.

　　Performance Characteristics of VMs vs Docker Containers by Boden Russel (IBM)

　Performance characteristics of traditional v ms vs docker containers

　The controversial part

　Any project will have arguments, just like Go, like NodeJS, and Docker also has it Some.

　Can it be completely isolated?

In a super complex business system, can a single OS achieve complete isolation? Will the crash/memory overflow/high CPU usage of one program affect other containers or the entire system? Many people are still skeptical about whether Docker can support mission-critical systems in an actual multi-host production environment. Note* Just like some people question that Node.JS single thread is fast and unstable and cannot be applied in complex scenarios.

But the good news is that the Linux kernel has made many improvements to Container to support better isolation.

　GO language is not yet fully mature

　Docker is developed by Go language, but GO language is relatively unfamiliar to most developers, and it is still improving, and it is still some time away from maturity. This half-git, half-package management approach makes some people uncomfortable.

　Controlled by a private company

　Docker was designed by a private company called Dotcloud. The companies are all for-profit. For example, you cannot use the source code to compile the Docker project. You can only use the Docker binary distribution package compiled by the black box. , the future may not be completely free. At present, Docker has launched enterprise-level services (consulting, support and training) for companies.