Hroot

Hroot provides transports and straightforward configuration files for Docker.
Strongly version your containers, then distribute them offline or over SSH & HTTP with git!

Docker's image storage is treated like a cache, while Hroot manages your images using git as a persistent storage backend. Your containers now have effortless history, strong hashes to verify integrity, git commit messages, and secure transport.

Further, ditch those long config flags and express them in a file instead. Hroot looks for a hroot.toml file in the current directory and sets up binds, mounts, etc. Add that file to your project's version control and get your entire team working on the same system.

Quickstart

Grab the latest release and throw it on your path. Alternately, build Hroot from source.

# Clone down some example config files
git clone https://github.com/polydawn/boxen.git && cd boxen

# Download ubuntu from public index, save into git
cd ubuntu-index && hroot build

# Build your own ubuntu image (updates apt-get)
cd ../ubuntu    && hroot build

# Load repeatable ubuntu from git and start an interactive shell
hroot run bash

You just built a git repo tracking ubuntu.

A new (bare) repository called graph has appeared in the boxen folder.
Push that anywhere and have your team clone it down!

How do I use it?

Hroot provides two commands to help you maintain & use images: build and run.

Using build will take an image from somewhere, execute a build step, and save the result.
Using run just runs an (already-built) image.

Getting started

First you'll need Docker, which you can get via their installation instructions.
Next, download Hroot and place it on your path:

# Run this from your download directory
sudo cp ./hroot /usr/bin/hroot

# Test that it's working
hroot version

Running containers with Hroot requires root, so you'll need to use sudo or launch a root shell for most commands. You'll also need a running Docker server - if you followed the linked instructions, one should already be running for you. Hroot tries to use the default server first, and starts one for you if it can't find one.

First steps

To use Hroot, you need a config file in the current directory called hroot.toml.
This file tracks all your image names and settings.

Our Boxen repository has several examples, which we'll use for this tutorial.
Clone it down if you haven't already:

# Clone down some prepared examples
git clone https://github.com/polydawn/boxen.git && cd boxen

In the boxen folder, there's the first config file. You'll notice there's only one section - settings. Here we set up a bunch of settings we want for pretty much every image: DNS servers, folder mounts, etc.

Because Hroot is smart, these settings apply to every image configured in Boxen. Hroot scans up parent folders, looking for hroot.toml files, and stops when it can't find one. Today, we'll be using ubuntu:

# Pop into the index ubuntu folder
cd ubuntu-index

You'll notice this next config file is different - it has image and target sections, with copious comments.
We'll explain each in turn:

Image names

The image section can have three entries: name, upstream, and index.

Entry	Purpose
Name	The name of the image, and the name of the branch that ends up in git. Example: polydawn.net/ubuntu/14.04
Upstream	This image's parent - where did it get built from? This is used by the build command. <p>A configuration file has either an Upstream or an Index key, but not both.</p> <p>Example: <code>index.docker.io/ubuntu/14.04</code> </td> </tr><tr> <tr> <td>Index</td> <td> <p><a href="https://index.docker.io">Docker index</a> names are not compatible with reasonable branch names.</p> <p>A prime example is "ubuntu", which would be confusing without specifying the difference between an unmodified ubuntu and one you've saved in the graph.</p> <p>For this reason, we store the upstream image's index alias separately, and <i>only</i> use that when pulling from the index.</p> <p>Example: <code>ubuntu:14.04</code></p> </td> </tr>

Targets

Targets tell Hroot what to do. They can be called anything, but two are special: build and run, which are the defaults used when you tell Hroot to... build & run!

Unlike the settings section, putting settings in a target only applies to that target. It does not affect other folders.
You can put any setting in a target, but the most common usage is to set a different command.

You'll notice that in the current folder, trying hroot run will just echo out an example message, while hroot run bash will launch a bash shell.

Of course, neither will work right now - Hroot can't find your image! We need to get ourselves an image.

Bootstrapping from the index

Most of the time, you'll want to fork & version an image from the public docker index. We support plain tarballs as well (more on that later), but the index can be convenient. This is what the index conf file is ready to do.

Try the following:

# Download ubuntu from public index, save into git
hroot build

This command accomplished a few things:

• Hroot chose the public index as the source, and looked there for an image called ubuntu:14.04
• A small build script cleaned out apt-get state from the index image that we don't want to save in history.
• Once downloaded, Hroot saved that image to the graph destination.
• Odds are you didn't have a graph repository, so Hroot created one for you.

You now have a (bare) git repository called graph in the boxen folder!
If you check out the log, you'll have a single commit with the image's branch name:

$ ( cd ../graph ; git log --graph --decorate )

* commit 7105d5622bf8118af1c13001f2b36d51a93f020e (index.docker.io/ubuntu/14.04)
  Author: Your Name <you@example.com>

      index.docker.io/ubuntu/14.04 imported from an external source

You can push this repository anywhere & share it with the world. Whoever receives it can validate the hash and have a guarantee it's the same image.

Sources & destinations:

Our example used the index as a source and a local graph as the destination. Hroot supports a few others:

Type	Purpose
Graph	A git repository used to version images. (default)
File	A tarball created from docker export.
Docker	The local docker daemon's cache.
Index	The public index.

This makes it easy to load & save images in a variety of ways. Use the appropriate strategy for your situation.

You can set these with the -s and -d flags, otherwise Hroot will choose smart defaults.

Building an image

We're now ready to fork the image we downloaded and walk our own (strongly-versioned) path.

# Navigate to the main ubuntu folder
cd ../ubuntu

# Upgrade apt-get packages & save the new ubuntu image
hroot build

This will plug away for awhile (you're updating all the ubuntu packages!) and accomplish a few things:

• Hroot imported the image from the graph.
• The Docker daemon now knows about index.docker.io/ubuntu, not just ubuntu.
• The build.sh file ran a couple scripts around apt-get, upgrading packages.
• After building, Hroot saved our new image to the graph.
• We now have a new branch name, starting with example.com/ubuntu.

Your git log has a new commit listed:

$ ( cd ../graph ; git log --graph --decorate )

* commit 2a9c8a28220717790de7336d07f86e9857074509 (HEAD, example.com/ubuntu/14.04)
| Author: Your Name <you@example.com>
|
|     example.com/ubuntu/14.04 updated from index.docker.io/ubuntu/14.04
|
* commit 7105d5622bf8118af1c13001f2b36d51a93f020e (index.docker.io/ubuntu/14.04)
  Author: Your Name <you@example.com>

      index.docker.io/ubuntu/14.04 imported from an external source

Notice how you now have two branches, named after their respective images. This git repository will track which image was built from where, using merges - an audit log, built into the log graph.

Now you can play around with hroot images. Launch a bash shell and experiment!

# Load repeatable ubuntu from git and start an interactive shell
hroot run bash

What's next?

From here, we strongly recommend playing around more with the example Boxen folders. There's several images pre-configured there, for example a zero-config nginx server. Additions to that repository are welcome!

When you're ready to use Hroot with your own team, simply write your own hroot.toml file and place it in a new folder. Build yourself an image (perhaps copying one of our build.sh scripts?) and share your machine with the world!

Building from source

To build Hroot, you will need Go 1.2 or newer. Following the golang instructions for 64-bit linux:

curl https://go.googlecode.com/files/go1.2.linux-amd64.tar.gz -o golang.tar.gz
sudo tar -C /usr/local -xzf golang.tar.gz
export PATH=$PATH:/usr/local/go/bin # Add this to /etc/profile or similar

Clone down Hroot & throw it on your path:

git clone https://github.com/polydawn/hroot && cd hroot
git submodule update --init

./goad build
sudo cp hroot/hroot /usr/bin/hroot

Now you're ready to rock & roll. Lots of examples are available over at Boxen!

Installing Docker

Hroot uses Docker, an excellent container helper based on LXC. This gives Hroot all that containerization mojo. We're using Docker 0.11.1 right now.

Docker offers a variety of installation instructions on their site.