Docker #2

Docker containers have their own kernel or not?

도커 컨테이너는 자신만의 커널을 가지고 있는가? No

Docker uses host OS kernel, there is no custom or additional kernel inside container. All containers which run on a machine are sharing this "host" kernel.

Host OS 커널을 공유한다. 대신 VM 보다 효율적으로 관리되어서 성능이 좋다. 

Wikipedia says http://en.wikipedia.org/wiki/Docker_(software) that

Docker uses resource isolation features of the Linux kernel such as cgroups and kernel namespaces to allow independent "containers" to run within a single Linux instance, avoiding the overhead of starting virtual machines.

cgroups, namespaces and LXC are features of Linux kernel to isolate groups of processes; there is still single kernel, single scheduler, and one instance of kernel memory manager.

Boot2docker and CoreOS are just lightweight Linux distributions with some host kernel; they can be used to load Docker containers.

http://boot2docker.io/

boot2docker is a lightweight Linux distribution based on Tiny Core Linux made specifically to run Docker containers. It runs completely from RAM, weighs ~27MB and boots in ~5s (YMMV).

http://en.wikipedia.org/wiki/CoreOS

A single control host (CoreOS instance) runs multiple isolated Linux systems (containers), using Docker as an additional layer of abstraction and interface[14] to the underlying operating-system-level virtualization features of the Linux kernel. ... This approach relies on the Linux kernel's cgroups functionality, which provides namespace isolation and abilities to limit, account and isolate resource usage (CPU, memory, disk I/O, etc.) for the collections of processes.