This guide contains instructions for those looking to hack on rkt.
For more information on the rkt internals, see the devel documentation.
You should be able build rkt on any modern Linux system. For the most part the codebase is self-contained (e.g. all dependencies are vendored), but assembly of the stage1 requires some other tools to be installed on the system. Please see the list of the build-time dependencies. Once the dependencies have been satisfied you can build rkt by running the following commands:
git clone https://github.com/coreos/rkt.git
cd rkt
./autogen.sh && ./configure && make
Build verbosity can be controlled with the V variable.
Set V to 0 to have a silent build.
Set V to either 1 or 2 to get short messages about what is being done (level 2 prints more of them).
Set V to 3 to get raw output.
Instead of a number, english words can be used.
quiet or silent for level 0, info for level 1, all for level 2 and raw for level 3. Example:
make V=raw
To be able to run rkt, please see the list of the run-time dependencies.
Alternatively, you can build rkt in a Docker container with the following command. Replace $SRC with the absolute path to your rkt source code:
# docker run -v $SRC:/opt/rkt -i -t golang:1.5 /bin/bash -c "apt-get update && apt-get install -y coreutils cpio squashfs-tools realpath autoconf file xz-utils patch bc && cd /opt/rkt && go get github.com/appc/spec/... && ./autogen.sh && ./configure && make"
By default, rkt gets systemd from a CoreOS image to generate stage1.
But it's also possible to build systemd from the sources.
To do this, use the following configure parameters after running ./autogen.sh:
--with-stage1-flavors--with-stage1-default-flavor(optional)--with-stage1-systemd-version--with-stage1-systemd-src
For more details, see configure script parameters documentation. Example:
./autogen.sh && ./configure --with-stage1-flavors=src --with-stage1-systemd-version=master --with-stage1-systemd-src=$HOME/src/systemd && make
The stage1 kvm image is based on CoreOS, but with additional components for running containers on top of a hypervisor.
To build, pass kvm to --with-stage1-flavors parameter in ./configure
This will generate stage1 with embedded kernel and kvmtool to start pod in virtual machine.
Additional build dependencies for the stage1 kvm follow.
If building with docker, these must be added to the apt-get install command.
- wget
- xz-utils
- patch
- bc
rkt is designed and intended to be modular, using a staged architecture.
rkt run determines the stage1 image it should use via its --stage1-{url,path,name,hash,from-dir} flags.
If this flag is not given to rkt, the stage1 image will default to the settings taken from the configuration.
If those are unset, rkt will fall back to the settings configured when rkt was built from source.
It usually means that rkt will look for a file called stage1-<default flavor>.aci that is in the same directory as the rkt binary itself.
However, a default value can be set for this parameter at build time by setting the option --with-stage1-default-location when invoking ./configure.
It can be set with the paths kind of configuration.
For more details, see configure script parameters documentation and configuration documentation.
rkt uses godep to manage third-party dependencies.
The build process is crafted to make this transparent to most users (i.e. if you're just building rkt from source, or modifying any of the codebase without changing dependencies, you should have no need to interact with godep).
But occasionally the need arises to either a) add a new dependency or b) update/remove an existing dependency.
There are two types of dependencies:
- libraries - Go code imported by some Go source file in the repository
- applications - Go code that we need to build to get some executable binary; this means that we want to "import" a "main" package.
We might want to vendor an application for several reasons:
- it will be used at build-time (like actool to build stage1 images)
- it will be a part of a stage1 image (like CNI plugins for networking)
- it will be used in functional tests (like ACE validator)
At this point, the ramblings below from an experienced Godep victim^Wenthusiast might prove of use...
Step zero is generally to ensure you have the latest version of godep available in your PATH.
To work with godep, you'll need to have the repository (i.e. github.com/coreos/rkt) checked out in a valid GOPATH.
If you use the standard Go workflow, with every package in its proper place in a workspace, this should be no problem.
As an example, if one was obtaining the repository for the first time, one would do the following:
$ export GOPATH=/tmp/foo # or any directory you please
$ go get -d github.com/coreos/rkt/... # or 'git clone https://github.com/coreos/rkt $GOPATH/src/github.com/coreos/rkt'
$ cd $GOPATH/src/github.com/coreos/rkt
If, however, you instead prefer to manage your source code in directories like ~/src/rkt, there's a problem: godep doesn't like symbolic links (which is what the rkt build process uses by default to create a self-contained GOPATH).
Hence, you'll need to work around this with bind mounts, with something like the following:
$ export GOPATH=/tmp/foo # or any directory you please
$ mkdir -p $GOPATH/src/github.com/coreos/rkt
# mount --bind ~/src/rkt $GOPATH/src/github.com/coreos/rkt
$ cd $GOPATH/src/github.com/coreos/rkt
One benefit of this approach over the single-workspace workflow is that checking out different versions of dependencies in the GOPATH (as we are about to do) is guaranteed to not affect any other packages in the GOPATH.
(Using gvm or other such tomfoolery to manage GOPATHs is an exercise left for the reader.)
Now that we have a functional GOPATH, use godep to restore the full set of vendored dependencies to their correct versions.
(What this command does is essentially just loop over the set of dependencies codified in Godeps/Godeps.json, using go get to retrieve and then git checkout (or equivalent) to set each to their correct revision.)
$ godep restore # might take a while if it's the first time...
At this stage, your path forks, depending on what exactly you want to do: add, update or remove a dependency, or add, update or remove an application. But in all six cases, the procedure finishes with the same save command.
In this case you'll first need to retrieve the dependency you're working with into GOPATH.
As a simple example, assuming we're adding github.com/fizz/buzz/tazz:
$ go get -d github.com/fizz/buzz
Add the new dependency into godep's purview by simply importing the standard package name in one of your sources:
$ vim $GOPATH/src/github.com/coreos/rkt/some/file.go
...
import "github.com/fizz/buzz/tazz"
...
Now, GOTO saving
Add the new application to the vendoredApps file in the root of the repository:
$ vim vendoredApps
...
github.com/fizz/buzz/tazz
...
Now, GOTO saving
The steps here are the same for both libraries and applications.
In this case, assuming we're updating github.com/foo/bar:
$ cd $GOPATH/src/github.com/foo/bar
$ git pull # or 'go get -d -u github.com/foo/bar/...'
$ git checkout $DESIRED_REVISION
$ cd $GOPATH/src/github.com/coreos/rkt
$ godep update github.com/foo/bar/...
Now, GOTO saving
This is the simplest case of all.
Simply remove all references to a dependency from the source files.
Now, GOTO saving
Simply remove the relevant line from the vendoredApps file.
Now, GOTO saving
Finally, here we are, the magic command, the holy grail, the ultimate conclusion of all godep operations.
Provided you have followed the preceding instructions, regardless of whether you are adding/removing/modifying dependencies, this innocuous script will cast the necessary spells to solve all of your dependency worries:
$ ./scripts/godep-save
rkt attempts to offer consistent and structured error output. To achieve this, we use a couple helper types which we'll describe below.
rkt uses the errwrap package to structure errors. This allows us to manage how we output errors. You can wrap errors by doing the following.
err := funcReturningSomeError()
errwrap.Wrap(errors.New("My new error"), err)
For writing to output rkt uses its own log package which is essentially a wrapper around the golang log package. This is used to write to both stderr and stdout. By doing this, rkt can easily change the way it formats its output.
A few new methods are added to control the output of the wrapped errors. For example, the following outputs an error to stderr.
log := rktlog.Logger(os.Stderr, "rkt", debug)
log.PrintE("a message to accompany the error", err)
There are similar functions named FatalE, PanicE. All the other methods from golang's log package are available.
In order to write to stdout, we also use the rkt log package. If not already set up in your package, one can be created as follows.
stdout := rktlog.Logger(os.Stdout, "", false)
Here, the prefix is an empty string and debug is set to false.
At this point, you should be good to submit a PR. As well as a simple sanity check that the code actually builds and tests pass, here are some things to look out for:
git status Godeps/should show only a minimal and relevant change (i.e. only the dependencies you actually intended to touch).git diff Godeps/should be free of any changes to import paths within the vendored dependenciesgit diffshould show all third-party import paths prefixed withGodeps/_workspace
If something looks awry, restart, pray to your preferred deity, and try again.