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This article will explain in detail the history and current situation and principles and concepts of docker. The content of the article is of high quality, so the editor will share it with you for reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

Analysis of the History and present situation of 1.docker

Limitations and dilemmas of the older generation of PASS platform:

Mainly provide application deployment and hosting, for application developers, only support specific LAAS basic technologies, support a single development language and framework, support specific services, such as custom data storage APIs, do not well solve the deployment of common middleware, it is difficult to solve the problem of isolation of applications and resources.

New generation PAAS platform:

Comprehensive application lifecycle management, focusing on openness, application portability and cloud interoperability, including Cloud Foundry, OpenShift, Docker, Heroku, MoPass and other technologies or services, with most of the following characteristics (multi-language and framework, multi-service, multi-cloud and multi-laaS technology)

Docker is called the third generation Paas platform.

Docker was officially released on March 27, 2013.The contribution to github has grown rapidly, and 2013.10dotCloud has changed its name to docker.

Introduction to the Technical principle of 2.docker

Docker is a lightweight alternative to virtualization. The docker container does not rely on any language, framework, or system, and can turn APP into a standardized, portable, self-managed component that can be developed, debugged and run in any mainstream system without server hardware.

Quickly create a container on the linux system, deploy and run the application on the container, and through the configuration file can easily realize the automatic installation, deployment and upgrade of the application, which is very convenient. It is convenient to separate the production and development environment.

Core technology of docker: cgroups

Cgroups is controller group, and there is often a requirement in linux systems that wants to limit the allocation of resources for one or some processes. So it is the concept of cgroups, in this group, there is a specific proportion of cpu time, IO time, available memory, and so on. Cgroups is a linux kernel function that manages arbitrary processes in groups. It was proposed by google engineers and later integrated into the linux kernel.

Core technology of docker: LXC

LXC, which stands for linux container, is a container-based virtualization technology at the operating system level. With the isolation mechanism of namespace and the quota function of cgroups, lxc provides a set of unified API and tools to establish and manage container. Compared with other virtual technologies at the operating system level, the biggest advantage of LXC is that LXC is integrated into the kernel without having to patch the kernel separately.

LXC aims to provide an OS-level virtualization method of sharing kernel, without repeatedly loading kernel during execution, and container's kernel is shared with host, thus greatly speeding up the startup process of container and significantly reducing memory consumption, as well as saving resource overhead by sharing resources, which means that containerization costs much less than real virtualization. In the actual test, the IO and CPU performance of the LXC-based virtualization method is almost close to that of baremetal. But if the kernel stops, all containers will stop running.

Core technology of docker: AUFS

AuFS is a layered file system that transparently overwrites one or more existing file systems. Support to mount different directories to the same virtual file system, you can combine different directories together to form a single directory. This is a virtual file system, which can be mounted directly without formatting.

Docker has been using AuFS as the container's file system. When a process needs to modify a file, AuFS creates a copy of the file. AuFS can combine multiple layers into a single-layer representation of a file system. This process is called write replication.

AuFS allows docker to use certain images as the basis for the container. Can save storage and memory, but also ensure faster container deployment.

Another benefit of using AuFS is the version container mirroring capability of docker.

Docker principle: APP Packaging

On the basis of LXC, the additional functions provided by docker include a standard and unified package deployment plan. In order to maximize the reuse of image, speed up the running speed, and reduce memory and disk footprint, the runtime environment constructed by the docker container runtime is actually composed of multiple layer with dependencies. With hierarchical image as the basis, different APP can share underlying file systems, related dependent tools, etc., and different instances of the same APP can also share most of the data, and then maintain the modified data in the form of copy on write.

Docker lifecycle development model:

Docker is rapidly changing the rules of operation in the field of cloud computing, from continuous integration / continuous delivery to micro-services, open source collaboration, to DevOps, docker has brought great changes to the application development life cycle and cloud engineering computing practices.

3. The basic concept of docker

Docker image:

Docker image is an extremely stripped-down version of the linux program running environment. Docker image is an "installation package" that needs to be customized to build, including a binary deployment package for basic images + applications. Configuration files that need to be modified at run time are not recommended in docker image.

Dockerfile is used to create a custom image, including user-specified software dependencies, etc. One of the best practices of docker iamges is to reuse and use online corporate images as much as possible.

Docker container:

Docker container is an instance of image that shares the kernel. In docker container, you can run image of different OS, such as ubuntu or centos. Docker1.3 added docker exec command to enter the container to troubleshoot the problem. Docker container has no IP address, usually no service port exposure, and is a closed box / sandbox.

Docker Lifecycle:

Docker daemon:

Docker daemon is the linux daemon that creates and runs container and is the most important core component of docker. Docker daemon can bind local ports and provide rest api services for remote access and control.

Docker registry/hub:

About the history and status quo of docker and what the principles and concepts are shared here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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