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Dear packager.
If you are looking to make docker available on your favorite software distribution, this document is for you. It summarizes the requirements for building and running docker.
Getting started
We really want to help you package Docker successfully. Before anything, a good first step is to introduce yourself on the docker-dev mailing list , explain what you''re trying to achieve, and tell us how we can help. Don''t worry, we don''t bite! There might even be someone already working on packaging for the same distro!
You can also join the IRC channel - #docker and #docker-dev on Freenode are both active and friendly.
Package name
If possible, your package should be called "docker". If that name is already taken, a second choice is "lxc-docker".
Official build vs distro build
The Docker project maintains its own build and release toolchain. It is pretty neat and entirely based on Docker (surprise!). This toolchain is the canonical way to build Docker, and the only method supported by the development team. We encourage you to give it a try, and if the circumstances allow you to use it, we recommend that you do.
You might not be able to use the official build toolchain - usually because your distribution has a toolchain and packaging policy of its own. We get it! Your house, your rules. The rest of this document should give you the information you need to package Docker your way, without denaturing it in the process.
System build dependencies
To build docker, you will need the following system dependencies
- An amd64 machine
- A recent version of git and mercurial
- Go version 1.2 or later
- SQLite version 3.7.9 or later
- libdevmapper version 1.02.68-cvs (2012-01-26) or later from lvm2 version 2.02.89 or later
- btrfs-progs version 3.8 or later (including commit e5cb128 from 2013-01-07) for the necessary btrfs headers
- A clean checkout of the source must be added to a valid Go workspace under the path src/github.com/dotcloud/docker.
Go dependencies
All Go dependencies are vendored under ./vendor. They are used by the official build, so the source of truth for the current version is whatever is in ./vendor.
To use the vendored dependencies, simply make sure the path to ./vendor is included in $GOPATH.
If you would rather package these dependencies yourself, take a look at ./hack/vendor.sh for an easy-to-parse list of the exact version for each.
NOTE: if you''re not able to package the exact version (to the exact commit) of a given dependency, please get in touch so we can remediate! Who knows what discrepancies can be caused by even the slightest deviation. We promise to do our best to make everybody happy.
Stripping Binaries
Please, please, please do not strip any compiled binaries. This is really important.
See the following quotes from Dave Cheney, which explain this position better from the upstream Golang perspective.
go issue #5855, comment #3
Super super important: Do not strip go binaries or archives. It isn't tested, often breaks, and doesn't work.
launchpad golang issue #1200255, comment #8
To quote myself: "Please do not strip Go binaries, it is not supported, not tested, is often broken, and doesn't do what you want"
To unpack that a bit
- not supported, as in, we don't support it, and recommend against it when asked
- not tested, we don't test stripped binaries as part of the build CI process
- is often broken, stripping a go binary will produce anywhere from no, to subtle, to outright execution failure, see above
launchpad golang issue #1200255, comment #13
To clarify my previous statements.
- I do not disagree with the debian policy, it is there for a good reason
- Having said that, it stripping Go binaries doesn't work, and nobody is looking at making it work, so there is that.
Thanks for patching the build formula.
Building Docker
To build the docker binary, run the following command with the source checkout as the working directory:
./hack/make.sh binary
This will create a static binary under ./bundles/$VERSION/binary/docker-$VERSION, where $VERSION is the contents of the file ./VERSION.
You are encouraged to use ./hack/make.sh without modification. If you must absolutely write your own script (are you really, really sure you need to? make.sh is really not that complicated), then please take care the respect the following:
- In ./hack/make.sh: $LDFLAGS, $BUILDFLAGS, $VERSION and $GITCOMMIT
- In ./hack/make/binary: the exact build command to run
You may be tempted to tweak these settings. In particular, being a rigorous maintainer, you may want to disable static linking. Please don''t! Docker needs to be statically linked to function properly. You would do the users of your distro a disservice and "void the docker warranty" by changing the flags.
A good comparison is Busybox: all distros package it as a statically linked binary, because it just makes sense. Docker is the same way.
If you must have a non-static Docker binary, please use:
./hack/make.sh dynbinary
This will create ./bundles/$VERSION/dynbinary/docker-$VERSION and ./bundles/$VERSION/binary/dockerinit-$VERSION. The first of these would usually be installed at /usr/bin/docker, while the second must be installed at /usr/libexec/docker/dockerinit.
Testing Docker
Before releasing your binary, make sure to run the tests! Run the following command with the source checkout as the working directory:
./hack/make.sh test
The test suite includes both live integration tests and unit tests, so you will need all runtime dependencies to be installed (see below).
The test suite will also download a small test container, so you will need internet connectivity.
Dependencies
Runtime
To run properly, docker needs the following software to be installed at runtime:
- iproute2 version 3.5 or later (build after 2012-05-21), and specifically the "ip" utility
- iptables version 1.4 or later
- Git version 1.7 or later
- XZ Utils 4.9 or later
Kernel
Docker in daemon mode has specific kernel requirements. Most pre-packaged kernels include the necessary options enabled. If you are building your own kernel, you will either need to discover the options necessary via trial and error, or check out the Gentoo ebuild, in which a list is maintained.
Note that Docker also has a client mode, which can run on virtually any linux kernel (it even builds on OSX!).
Optional
Some of Docker's features are activated by using optional command-line flags or by having support for them in the kernel or userspace. A few examples include:
- LXC execution driver (requires version 0.8 or later of the LXC utility scripts)
- AUFS graph driver (requires AUFS patches/support enabled in the kernel, and at least the "auplink" utility from aufs-tools)
- BTRFS graph driver (requires BTRFS support enabled in the kernel)
Init script
Docker expects to run as a daemon at machine startup. Your package will need to include a script for your distro's process supervisor of choice. Be sure to check out the "contrib/init" folder in case a suitable init script already exists!
In general, Docker should be run as root, with the following arguments:
docker -d