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Comment by agilebyte | Hacker News Reader

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agilebyte·

The way I think about it:

Docker - specify a config file and boom you have a VM with the system, the language, the libraries preinstalled

Deis/Dokku - gives you tooling to deploy/stop/access apps on your VM with an easy cli

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Ok.. But if I push 5 docker containers based on say Ubuntu 14.04, will they take 5 times the size of an Ubuntu 14.04 base install, or will they share base install?

They will share, and will spin up very fast, so size is not an issue.

They share much of the underlying OS.

A little Docker example I keep coming back to:

https://github.com/radekstepan/im-runnable

It creates a little service that lets you run code (like Python, Node) in Docker sandboxed environment.

this is more of a Docker than a Deis question, but a Docker image is composed of layers. Each tagged image keeps an ancestry list of all of the layers it requires. In your case, if you run 5 docker containers on the same host on top of ubuntu:14.04, it will initially pull the parent's layers (ubuntu:14.04), then it will pull its own layers. They all share the same layers, which is why it's so powerful. You get the exact same execution environment every time.

Key here is to realize the difference between VMs and LXC (which is what Docker builds on).

Clarifying note: Docker uses libcontainer NY default for its execution engine. LXC is an option, not enabled by default.

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