ROS 2 applications

ROS 2 is distributed via Open Robotics’ own Debian archive, along with many community-supported tools. It’s possible to get your own application into their archive as well, but it requires that the application is open-source.

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

There are currently two supported bases for ROS, core18 and core20.

core18 is based on Ubuntu 18.04 LTS.

core20 is based on Ubuntu 20.04 LTS.

Let us explore the differences between core18 and core20.

core18

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: 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: dashing
    colcon-rosdistro: dashing
    colcon-source-space: demo_nodes_cpp
    stage-packages: [ros-dashing-ros2launch]

apps:
  ros2-talker-listener:
    command: opt/ros/dashing/bin/ros2 launch demo_nodes_cpp talker_listener.launch.py

You can download the example repository with the following command:

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

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: 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.

For more information about top level metadata, see, top-level-metadata.

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. It is therefore the base for ROS Melodic and ROS 2 Dashing snaps.

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.

confinement: devmode

For more information about security model, see, choosing-a-security-model.

Parts

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

Snapcraft relies on well known and well established ROS tools such as, in this example, colcon.

Note: It is easy to forget the importance of complete install rules, i.e. rules for installing every component of the package necessary to run, or every component necessary to use a given library.

The packages you’re building must have install rules, or else snapcraft won’t know which components to place into the snap. Make sure you install binaries, libraries, header files, launch files, etc.

parts:
  ros-demos:
    plugin: colcon
    source: https://github.com/ros2/demos.git
    source-branch: dashing
    colcon-rosdistro: dashing
    colcon-source-space: demo_nodes_cpp
    stage-packages: [ros-dashing-ros2launch]

For more details on colcon-specific metadata, see The colcon plugin. For more information about general parts metadata, see, parts-metadata.

Apps

Apps are the commands and services exposed to end users. Each entry under apps is the command name that should be exposed to the end users.

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:
  ros2-talker-listener:
    command: opt/ros/dashing/bin/ros2 launch demo_nodes_cpp talker_listener.launch.py

In snap, an application is usually prefixed by the snap name so that the application my-app from the snap my-snap can be executed calling my-snap.my-app. However, if both the snap and the app are called the same, as is the case in our ROS2 example, the execution command collapses to avoid the tediousness of writing twice the same words. The command ros2-talker-listener.ros2-talker-listener simply becomes ros2-talker-listener.

Building the snap

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 ros2-talker-listener_0.1_amd64.snap

Warning: The warnings regarding missing libraries that you might see when building your snap are false positive. These libraries are build time dependencies only.

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 ros2-talker-listener_*.snap --devmode --dangerous

You can then try it out:

$ ros2-talker-listener
[INFO] [launch]: All log files can be found below /home/user/snap/ros2-talker-listener/x1/.ros/log/2022-03-09-15-33-33-276616-computer-1876564
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [talker-1]: process started with pid [1876618]
[INFO] [listener-2]: process started with pid [1876620]
[talker-1] [INFO] [1646836414.794632135] [talker]: Publishing: 'Hello World: 1'
[listener-2] [INFO] [1646836414.795643603] [listener]: I heard: [Hello World: 1]
[talker-1] [INFO] [1646836415.794321203] [talker]: Publishing: 'Hello World: 2'
[listener-2] [INFO] [1646836415.795037146] [listener]: I heard: [Hello World: 2]
[...]

Removing the snap is simple too:

$ sudo snap remove ros2-talker-listener

Once done developing your snap, you can easily clean up the build environment:

$ snapcraft clean
core20

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-core20. Don’t worry, we’ll break this down.

name: ros2-talker-listener
version: '0.1'
summary: ROS2 Talker/Listener Example
description: |
 This example launches a ROS2 talker and listener.
 
confinement: devmode
base: core20
 
parts:
 ros-demos:
   plugin: colcon
   source: https://github.com/ros2/demos.git
   source-branch: foxy
   source-subdir: demo_nodes_cpp
   stage-packages: [ros-foxy-ros2launch]
 
apps:
 ros2-talker-listener:
   command: opt/ros/foxy/bin/ros2 launch demo_nodes_cpp talker_listener.launch.py
   extensions: [ros2-foxy]

You can download the example repository with the following command:

$ git clone https://github.com/snapcraft-docs/ros2-talker-listener-core20

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: 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.

This is a declarative version of the packaged software and is not linked to the version of the snap itself. 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.

For more information about top level metadata, see, top-level-metadata.

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: core20

core20 is the current standard base for snap building and is based on Ubuntu 20.04 LTS. It is therefore the base for ROS Noetic and ROS 2 Foxy snaps.

Security model

To get started, we won’t confine this application. Unconfined applications, specified with devmode, can only be released to the “edge” channel.

confinement: devmode

For more information about security model, see, choosing-a-security-model.

Parts

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

Snapcraft relies on well known and well established ROS tools such as, in this example, colcon.

Note: It is easy to forget the importance of complete install rules, i.e. rules for installing every component of the package necessary to run, or every component necessary to use a given library.

The packages you’re building must have install rules, or else snapcraft won’t know which components to place into the snap. Make sure you install binaries, libraries, header files, launch files, etc.

parts:
 ros-demos:
   plugin: colcon
   source: https://github.com/ros2/demos.git
   source-branch: foxy
   source-subdir: demo_nodes_cpp
   stage-packages: [ros-foxy-ros2launch]

For more details on colcon-specific metadata, see The colcon plugin. For more information about general parts metadata, see, parts-metadata.

Apps

Apps are the commands and services exposed to end users. Each entry under apps is the command name that should be exposed to the end users.

The command specifies the path to the binary to be run. This is resolved relative to the root of your snap contents.

apps:
 ros2-talker-listener:
   command: opt/ros/foxy/bin/ros2 launch demo_nodes_cpp talker_listener.launch.py
   extensions: [ros2-foxy]

For more details about the ros2-foxy extension, see ros2-foxy extension.

In snap, an application is usually prefixed by the snap name so that the application my-app from the snap my-snap can be executed calling my-snap.my-app. However, if both the snap and the app are called the same, as is the case in our ROS2 example, the execution command collapses to avoid the tediousness of writing twice the same words. The command ros2-talker-listener.ros2-talker-listener simply becomes ros2-talker-listener.

Building the snap

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

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

Warning: The warnings regarding missing libraries that you might see when building your snap are false positive. These libraries are build time dependencies only.

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

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

You can then try it out:

$ ros2-talker-listener
[INFO] [launch]: All log files can be found below /home/user/snap/ros2-talker-listener/x1/.ros/log/2022-03-09-15-33-33-276616-computer-1876564
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [talker-1]: process started with pid [1876618]
[INFO] [listener-2]: process started with pid [1876620]
[talker-1] [INFO] [1646836414.794632135] [talker]: Publishing: 'Hello World: 1'
[listener-2] [INFO] [1646836414.795643603] [listener]: I heard: [Hello World: 1]
[talker-1] [INFO] [1646836415.794321203] [talker]: Publishing: 'Hello World: 2'
[listener-2] [INFO] [1646836415.795037146] [listener]: I heard: [Hello World: 2]
[...]

Removing the snap is simple too:

$ sudo snap remove ros2-talker-listener

Once done developing your snap, you can easily clean up the build environment:

$ snapcraft clean --enable-experimental-extensions

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 upload --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.

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