Introduction to Docker containers

Docker Overview

Docker is an open source software deployment solution;
Docker is also a lightweight application container framework;
Docker can package, publish, and run any application. This is also the product concept of Docker: Docker - Build, Ship, and Run Any App, Anywhere
Docker uses LXC (Namespace+CGroups), which implements lightweight design through image management mechanism based on the Namespace [resource isolation] and CGroups [resource control] technologies of the Linux kernel.

Docker composition

Docker consists of Docker server and Docker client. Docker includes the following components: container, image and repository, as shown in the following figure:

Docker vs VM

As a type of container, Docker is very different from traditional VMs. First, let's compare the two in terms of architecture:

By comparison, we can see that VM is actually an operating system virtualized (hypervisor) based on hardware, and multiple VMs share the underlying hardware resources. Docker uses Namespace and CGroups technology for isolation based on Linux, which allows Docker to run on both hardware operating systems and VMs. The difference between the two also determines the difference between the two. Here we summarize the differences between the two, as follows:

Since Docker has such a feature, what can Docker do? The figure below shows 8 scenarios of docker. Based on actual work, the author mainly uses docker to simplify the release process of existing products, reducing a lot of environment configuration work. Due to the isolation of docker, the application can be packaged into a docker image, and different versions of the same product can be packaged into different images, which also facilitates testing.

Therefore, looking at Docker from different positions, the changes brought by Docker are all-round.