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Comment by seiji | Hacker News Reader

"new idea" is a huge stretch. More accurate: "new idea to the mass hacker nerd HN market."

Solaris has had—for years—container based virtualization with local virtual network and de-duplicating file system snapshots you can tar up and send across machines.

It's new in that they made a nice abstraction on top of the Linux clone of Solaris containers then marketed the crap out of it so everybody became aware of non-VM compartmentalization and fine grained resource allocation.

In short: still awesome, but not "they invented it" new.

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That's what I thought too. It's just FreeBSD jails brought to Linux, finally.

But I was wrong. Start playing with it for a while, and you will realize that Docker is not just about jails on Linux. Docker is about making portable, self-contained apps easy. It's about making sharing those containers easy. It's about making using those containers easy.

The core technology consists of a jail, yes. But once you've worked with the Docker registry and the Dockerfile (and its wonderful caching mechanism), and experienced just how easy it is to get something up an running, you will see that Docker > jails. Docker is much more than that.

Solaris containers and FreeBSD jails are like the LXC technology. Docker, the suite of tools and utilities built on top of LXC, is what the new idea is.

Specifically, docker lets you build, define, and script new instances, and then to install and launch those instances with a single command, snapshot them, re-publish them, and so on. That's the real secret sauce behind docker.

Even for those of us who knew all about the capabilities in Linux and who used lxc already, it still packages things up nicely and makes lxc easy to use, in particular, easy for a team to use because not everybody needs to become an expert on the system config and lxc config. The expert writes a dockerfile, and everyone else can use it and manage their servers as a collection of capabilities, each one clearly defined in a dockerfile.

There is another sense in which the idea isn't new - the notion of an image in smalltalk environments provides a similar level of encapsulation as docker containers, except perhaps that running smalltalk images don't get assigned their own ip address. A metacello script is analogous to dockerfile.

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