Once you have built your first snap, you will probably want to learn more about snapcraft’s more advanced features. Having a look at our selection of demos is a good idea, as we want it to be a good showcase of what is possible and generally relevant.
Our showcase can be found in the actual source of
snapcraft itself. Check
it out by simply running:
git clone https://github.com/snapcore/snapcraft cd snapcraft/demos
Inspecting the source locally will make easier to build the demos and play around with them. (You can view them online as well.)
Playing around with the demos
If you just cloned the
snapcraft source and inspect the demos, you
can start off your explorations by reading the accompanying
file and running:
This will inform you of all the steps taken during the creation of the snap.
Defining your parts
Once you have noted down all the general information about your snap
(like description, summary information and everything else), naming
the individual parts will define the stucture of your
Think of parts as individual components of your snap: Where do you pull them
from? How are they built?
Prerequisites during the build
The example named
downloader-with-wiki-parts shows how very easy you can
make sure that the relevant build dependencies are installed:
The above will install the
libssl-dev package from the Ubuntu archive before
an attempted build. If you need a specific version of libssl-dev or a custom
build, you will need to specify a separate part.
Also note that the above will not define which libraries are shipped with the app. It merely makes sure you have all the relevant build tools installed.
Pulling and building
If you just intend to pull and build the source, take a look at the
example. In its
snapcraft.yaml file you can find just this one
parts: gopaste: plugin: go source: git://github.com/wisnij/gopaste/gopasted
It starts off with the name of the specific part (
gopaste here), the origin
of the part (it’s a
git URL) and how to build it (plugin:
Other possible scenarios would be Bazaar or Mercurial branches, or local
Mixing and matching plugins
An interesting example is
py2-project because it defines two parts
spongeshaker using the
python2 plugin, and
make-project using the
parts: spongeshaker: plugin: python2 source: git://github.com/markokr/spongeshaker.git make-project: plugin: make source: .
The example above mixes and matches parts of different origin. Locally it
provides a binary we intend to ship (the
sha3sum.py script) and a
Makefile (to install our script in the right place).
spongeshaker is a python library we will need to pull from git, build as
a python project and bundle along with our script.
A possible use-case for the above would be if you just intend to ship a small binary which you maintain, but require a library you need to build from git as opposed to simply including it from the Ubuntu archives.
What’s happening during the
snapcraft run is:
- Build it as a python project (which will include installing the python library in the right place).
make(from the local
Makefile) and thus installing our
sha3sum.pyscript in the right place.
Putting your parts in order
If your app is comprised of multiple parts, it might be necessary to build
and stage parts in a particular order. This can be done by using the
parts: pipelinetest: plugin: make source: lp:~mterry/+junk/pipelinetest after: - libpipeline libpipeline: plugin: autotools source: lp:~mterry/libpipeline/printf
In the case of the
libpipeline example above, the part named
will be built after
libpipeline. Especially if you need specific
functionality during a build or as part of checks during the
this will be handy.
If any part built using the
after keyword needs to explicitly access
assets in the stage directory with configuration flags (e.g.;
in the case of autotools) it can use of the
variable, like this:
parts: my-part: plugin: autotools source: . configflags: - --with-swig $SNAPCRAFT_STAGE/swig after: - swig swig: plugin: autotools source: ./swig
With snapcraft we want to make it easy to learn from other app vendors and re-use parts which have worked well for them.
downloader-with-wiki-parts example, you can see that the
part is built:
after: - curl
As we never define the
curl part in the above example,
check the Ubuntu Wiki,
which is where we currently host examples of successful snapcraft parts.
The build order in this case would be
If you are planning to provide binaries and services to the users of your apps, you need to specify them in your definition first. It’s just a matter of enumerating them.
godd example has one app:
apps: godd: command: ./bin/godd
The above will take care of making the script executable, adding it to the user’s path and install it in the right place.
For a simple service we can take a look at
apps: gopaste: command: bin/gopasted daemon: simple
You define a name for the service, describe it (so log messages are more descriptive), declare how to run the service and that’s it. For more thoughts on services and their security, visit the snappy policy.
Limiting the number of installed files
To check the list of files included in your snap, you can use
on the resulting
.snap file. If you find that certain files should not be
shipped to the user (download size being just one factor), you can
snapcraft which files to snap:
prime: - usr/lib/x86_64-linux-gnu/libgudev-1.0.so* - usr/lib/x86_64-linux-gnu/libobject-2.0.so* - usr/lib/x86_64-linux-gnu/libglib-2.0.so* - bin/godd*
godd further defines the list of files to be placed in the app
prime phase. As you can see above, globs (using asterisks as
wildcard characters) are a good way of handling complexities within the
webcam-webui example you can see the following part called
cam: plugin: go go-packages: - github.com/mikix/golang-static-http stage-packages: - fswebcam filesets: fswebcam: - usr/bin/fswebcam - lib - usr/lib go-server: - bin/golang-* stage: - $fswebcam - $go-server prime: - $fswebcam - $go-server - -usr/share/doc
stage definition you can see how named filesets are re-used
Another feature used in the
prime definition is an exclude (
in this case), meaning that files in these directories will not be installed.
Snapping node.js apps has never been this easy. Take a look at the
example and see how short and sweet it is. To bundle node packages, you simply
do something like:
parts: shout: plugin: nodejs node-packages: - shout
node-packages simply lists which packages (including their dependencies) to
add to the snap.