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Comment by dhaivatpandya | Hacker News Reader

I recently wrote an article that covers some of this ground: http://www.sitepoint.com/docker-for-rubyists/

The basic idea behind Docker is that you don't have to create another operating system in order to just separate your processes from each other. This leads to containers being much more lightweight than virtual machines but also significantly less powerful (i.e. powerful as in ability to do something, not in terms of performance) in some areas.

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Any chance you can elaborate on:

"(i.e. powerful as in ability to do something, not in terms of performance)"

Do you mean smaller units of functionality which perform at good levels? For example, I wouldn't want to deploy a large, monolithic service this way?

The need for containers is more narrow in scope than simply the size of them, but that they allow very simple isolation on a file-system level. It allows a very strict separation of concerns without requiring the sacrifice of resources of spinning up another VM.

One thing that occurs to me: containers don't get their own network stacks, so you can't use a transport-level protocol (e.g. SCTP) in a Docker "guest" if it isn't programmed into the Docker host kernel. Whereas VMs are routed to at the network level, so they can do whatever they want with the packets they receive.

I meant to say that VMs can do a deeper level of process isolation. They also perform complete hardware virtualization, which means you can run a completely different OS inside the VM. However, in terms of performance, VMs are not necessarily faster than containers at all tasks.

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