ROS2 applications

ROS 2 is still under heavy development, and publishing your own application to the ROS 2 archive is likely to remain difficult until development stabilises.

You’re also left with the question of how to update ROS 2 and your application on a robotic platform that has already been shipped. With snapcraft it’s just one command to bundle a specific ROS 2 version along with your application (proprietary or open-source) into a snap that works anywhere and can be automatically updated.

Why are snaps good for ROS 2 projects?

  • Snaps are easy to discover and install
    Millions of users can browse and install snaps graphically in the Snap Store or from the command-line.
  • Snaps install and run the same across Linux
    Bundle the exact versions of the tools you need, including ROS 2, along with all of your app’s dependencies, be they modules or system libraries.
  • Snaps automatically update to the latest version
    Four times a day, users’ systems will check for new versions and upgrade in the background.
  • Upgrades are not disruptive
    Because upgrades are not in-place, users can keep your app open as it’s upgraded in the background.
  • Upgrades are safe
    If your app fails to upgrade, users automatically roll back to the previous revision with data preserved.

Build a snap in 20 minutes

Ready to get started? By the end of this guide, you’ll understand how to make a snap of your app that can be published in the Snap Store, showcasing it to millions of Linux users.

:information_source: For a brief overview of the snap creation process, including how to install snapcraft and how it’s used, see Snapcraft overview. For a more comprehensive breakdown of the steps involved, take a look at Creating a snap.

Getting started

Snaps are defined in a single YAML file placed in the root folder of your project. The following example shows the entire snapcraft.yaml file for an example project, ros2-talker-listener. Don’t worry, we’ll break this down.

name: test-ros2-talker-listener
version: '0.1'
summary: ROS2 Talker/Listener Example
description: |
  This example launches a ROS2 talker and listener.

base: core18
confinement: devmode

parts:
  ros-demos:
    plugin: colcon
    source: https://github.com/ros2/demos.git
    source-branch: crystal
    colcon-rosdistro: crystal
    colcon-source-space: demo_nodes_cpp
    build-packages: [make, gcc, g++]
    stage-packages: [ros-crystal-ros2launch]

apps:
  run:
    command: opt/ros/crystal/bin/ros2 launch demo_nodes_cpp talker_listener.launch.py

Metadata

The snapcraft.yaml file starts with a small amount of human-readable metadata, which usually can be lifted from the GitHub description or project README.md. This data is used in the presentation of your app in the Snap Store.

name: test-ros2-talker-listener
version: '0.1'
summary: ROS2 Talker/Listener Example
description: |
  This example launches a ROS2 talker and listener.

The name must be unique in the Snap Store. Valid snap names consist of lower-case alphanumeric characters and hyphens. They cannot be all numbers and they also cannot start or end with a hyphen.

Versions carry no semantic meaning in snaps and this version is arbitrary. It’s also possible to write a script to calculate the version, or to take a tag or commit from a git repository.

The summary can not exceed 79 characters. You can use a chevron ‘>’ in the description key to declare a multi-line description.

Base

The base keyword defines a special kind of snap that provides a run-time environment with a minimal set of libraries that are common to most applications. They’re transparent to users, but they need to be considered, and specified, when building a snap.

base: core18

core18 is the current standard base for snap building and is based on Ubuntu 18.04 LTS.

Security model

To get started we won’t confine this application. Unconfined applications, specified with devmode, can only be released to the hidden “edge” channel where you and other developers can install them.

confinement: devmode

Parts

Parts define how to build your app. Parts can be anything: programs, libraries, or other assets needed to create and run your application. In this case we have one: ros-demos. Parts can point to local directories, remote git repositories, or tarballs.

The colcon plugin will bundle the requested version of the ROS 2 underlay in the snap. It will then use that bootstrapped ROS 2 to build the provided workspace, and install it into the snap.

parts:
  ros-demos:
    plugin: colcon
    source: https://github.com/ros2/demos.git
    source-branch: crystal
    colcon-rosdistro: crystal
    colcon-source-space: demo_nodes_cpp
    build-packages: [make, gcc, g++]
    stage-packages: [ros-crystal-ros2launch]

For more details on Colcon-specific metadata, see The colcon plugin.

Apps

Apps are the commands and services exposed to end users. If your Apps are the commands you want to expose to users and any background services your application provides. Each key under apps is the command name that should be made available on users’ systems.

The command specifies the path to the binary to be run. This is resolved relative to the root of your snap contents and automatically searches in the usr/sbin, usr/bin, sbin, and bin sub directories of your snap.

apps:
  run:
    command: opt/ros/crystal/bin/ros2 launch demo_nodes_cpp talker_listener.launch.py

If your command name matches the snap name, users will be able run the command directly. If the names differ, then apps are prefixed with the snap name (test-xsv.command-name, for example). This is to avoid conflicting with apps defined by other installed snaps.

If your application is intended to run as a service you simply add the line daemon: simple after the command keyword. This will automatically keep the service running on install, update and reboot.

You can request an alias on the Snapcraft forum if your command name and snap name do not match but you don’t want your command prefixed. These aliases are set up automatically when your snap is installed from the Snap Store.

Building the snap

You can download the example repository with the following command:

$ git clone https://github.com/snapcraft-docs/ros2-talker-listener

After you’ve created the snapcraft.yaml, you can build the snap by simply executing the snapcraft command in the project directory:

$ snapcraft
Using 'snapcraft.yaml': Project assets will be searched for from the 'snap' directory.
Launching a VM.
[...]
Snapped test-ros2-talker-listener_0.1_amd64.snap

The resulting snap can be installed locally. This requires the --dangerous flag because the snap is not signed by the Snap Store. The --devmode flag acknowledges that you are installing an unconfined application:

$ sudo snap install test-ros2-talker-listener_*.snap --devmode --dangerous

You can then try it out:

$ test-ros2-talker-listener.run 
[...]

Removing the snap is simple too:

$ sudo snap remove test-ros2-talker-listener

You can also clean up the build environment, although this will slow down the next initial build:

$ snapcraft clean

By default, when you make a change to snapcraft.yaml, snapcraft only builds the parts that have changed. Cleaning a build, however, forces your snap to be rebuilt in a clean environment and will take longer.

Publishing your snap

To share your snaps you need to publish them in the Snap Store. First, create an account on the dashboard. Here you can customise how your snaps are presented, review your uploads and control publishing.

You’ll need to choose a unique “developer namespace” as part of the account creation process. This name will be visible by users and associated with your published snaps.

Make sure the snapcraft command is authenticated using the email address attached to your Snap Store account:

$ snapcraft login

Reserve a name for your snap

You can publish your own version of a snap, provided you do so under a name you have rights to. You can register a name on dashboard.snapcraft.io, or by running the following command:

$ snapcraft register myrossnap

Be sure to update the name: in your snapcraft.yaml to match this registered name, then run snapcraft again.

Upload your snap

Use snapcraft to push the snap to the Snap Store.

$ snapcraft push --release=edge myrossnap_*.snap

If you’re happy with the result, you can commit the snapcraft.yaml to your GitHub repo and turn on automatic builds so any further commits automatically get released to edge, without requiring you to manually build locally.

Congratulations! You’ve just built and published your first ROS snap. For a more in-depth overview of the snap building process, see Creating a snap.

Last updated 2 months ago. Help improve this document in the forum.