docker underlying_tech

绝对绿茶

　　### Namespaces
　　
　　Docker利用命名域来提供隔离的集装箱.会提供很多命名域给集装箱.
　　
　　* The pid namespace:
　　Used for process numbering (PID: Process ID)
　　* The net namespace:
　　Used for managing network interfaces (NET: Networking)
　　* The ipc namespace:
　　Used for managing access to IPC resources (IPC: InterProcess Communication)
　　* The mnt namespace:
　　Used for managing mount-points (MNT: Mount)
　　* The uts namespace:
　　Used for isolating kernel / version identifiers. (UTS: Unix Timesharing System)
　　
　　### Control groups
　　
　　简称 `cgroups`. 让应用孤立地运行需要包含文件系统和资源。Control groups允许Docker在集装箱之间公平地分享硬件资源，如果需要，还可以设置限制等等。
　　
　　### UnionFS
　　这是由每个layer构成的文件系统，这会使得每个层都非常的轻巧和快速。
　　
　　### Containers
　　
　　组合所有这些组件的形式，我们称之为`libcontainer`,docker 也支持传统的 Linux containers like LXC。
　　
　　###集装箱如何工作
　　
　　当集装箱运行的时候在read-only的image上套一层readwrite层，使用UnionFS技术，来运行内部的。
　　
　　
　　如果运行这条命令
　　
　　`$ docker run -i -t ubuntu /bin/bash`
　　
　　Docker begins with:
　　
　　* Pulling the ubuntu image:
　　
　　Docker checks for the presence of the ubuntu image and if it doesn't exist locally on the host, then Docker downloads it from Docker.io
　　
　　* Creates a new container:
　　Once Docker has the image it creates a container from it.
　　
　　* Allocates a filesystem and mounts a read-write layer:
　　The container is created in the filesystem and a read-write layer is added to the image.
　　
　　* Allocates a network / bridge interface:
　　Creates a network interface that allows the Docker container to talk to the local host.
　　
　　* Sets up an IP address:
　　Intelligently finds and attaches an available IP address from a pool.
　　
　　* Executes a process that you specify:
　　Runs your application, and;
　　
　　* Captures and provides application output:
　　Connects and logs standard input, outputs and errors for you to see how your application is running.
　　
　　### 镜像如何工作