How is Docker different from a virtual machine?

Question

I keep rereading the Docker documentation to try to understand the difference between Docker and a full VM. How does it manage to provide a full filesystem, isolated network

Answer 1

Through this post we are going to draw some lines of differences between VMs and LXCs. Let's first define them.

VM:

A virtual machine emulates a physical computing environment, but requests for CPU, memory, hard disk, network and other hardware resources are managed by a virtualization layer which translates these requests to the underlying physical hardware.

In this context the VM is called as the Guest while the environment it runs on is called the host.

LXCs:

Linux Containers (LXC) are operating system-level capabilities that make it possible to run multiple isolated Linux containers, on one control host (the LXC host). Linux Containers serve as a lightweight alternative to VMs as they don’t require the hypervisors viz. Virtualbox, KVM, Xen, etc.

Now unless you were drugged by Alan (Zach Galifianakis- from the Hangover series) and have been in Vegas for the last year, you will be pretty aware about the tremendous spurt of interest for Linux containers technology, and if I will be specific one container project which has created a buzz around the world in last few months is – Docker leading to some echoing opinions that cloud computing environments should abandon virtual machines (VMs) and replace them with containers due to their lower overhead and potentially better performance.

But the big question is, is it feasible?, will it be sensible?

a. LXCs are scoped to an instance of Linux. It might be different flavors of Linux (e.g. a Ubuntu container on a CentOS host but it’s still Linux.) Similarly, Windows-based containers are scoped to an instance of Windows now if we look at VMs they have a pretty broader scope and using the hypervisors you are not limited to operating systems Linux or Windows.

b. LXCs have low overheads and have better performance as compared to VMs. Tools viz. Docker which are built on the shoulders of LXC technology have provided developers with a platform to run their applications and at the same time have empowered operations people with a tool that will allow them to deploy the same container on production servers or data centers. It tries to make the experience between a developer running an application, booting and testing an application and an operations person deploying that application seamless, because this is where all the friction lies in and purpose of DevOps is to break down those silos.

So the best approach is the cloud infrastructure providers should advocate an appropriate use of the VMs and LXC, as they are each suited to handle specific workloads and scenarios.

Abandoning VMs is not practical as of now. So both VMs and LXCs have their own individual existence and importance.