docker_practice/introduction/what.md

What is Docker

Docker is an in-company project launched by Solomon Hykes who is the founder of dotCloud when he was in France, it's a revolution based on dotCloud's years of cloud service experience, and opened source with Apache 2.0 in 2013.03 maintained in GitHub. Then, Docker joined the Linux Foundation and promoted Open Containers Initlative (OCI).

Docker has aroused widespread concern and discussion and had 5.2w stars and 1w forks in it's GitHub since it opening source.At the end of 2013, dotCloud even decided to rename to Docker due to the popularity of the project. Docker was developed in Ubuntu 12.04 at the beginning. Red Hat has supported Dokcer since RHEL 6.5. Google also widely applies Docker in its PaaS products.

Docker develops with GO launched by Google, based on cgroup and namespace of Linux Kernel and Union FS like AUFS to package and isolate the processes which is belong to Operating system level virtualization technology. It is also called container because of the isolated process is independent of the host and other isolated processes. The initial implementation is based on LXC. It removed LXC and use libcontainer instead which is developed by themself since 0.7. Starting with 1.11, it uses runC and containerd further.

runc is a Linux command-line tool for creating and running containers according to the OCI container runtime specification.

containerd is a daemon that manages container life cycle from downloading and unpacking the container image to container execution and supervision.

Docker is further packaged on a container basis, from file system, network interconnection to process isolation, etc, greatly simplifying container craetion and maintenance.

The images below compare the differences between Docker and Traditional Virtualization. The traditional Virtual machine technology is to virtualize a set of hadware to run a complete operation system and run the required application process on this system. The application process in the container runs directly on the host kernel, and the container does not have its own Kernel and hadware virtualiztion. Therefore, container are lighter than traditional virtual machines.