The .NET toolchain makes it easy for developers to build and publish applications. However, end user discovery and update management remain a challenge. Snap helps fill this gap by letting developers distribute applications and its updates in an app store experience for end users.
Why are snaps good for .NET 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 They bundle the exact version of .NET required, along with all of your app’s dependencies, be they .NET DLLs 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 version.
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 .NET app that can be published in the Snap Store, showcasing it to millions of Linux users.
Snapcraft overview: 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.
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. A complete reference of the available options for this file can be found in the Snapcraft.yaml reference. The following example shows the entire snapcraft.yaml file for an existing project, whatime. Don’t worry, we’ll break this down.
name: whatime
version: '1.0.0'
grade: devel
summary: Get the current time in various cities around the world
description: |
Whatime is able to get you the current time in several different cities
around the world.
base: core22
confinement: devmode
parts:
whatime:
plugin: dotnet
dotnet-build-configuration: Release
dotnet-self-contained-runtime-identifier: linux-x64
source: .
build-packages:
- dotnet-sdk-6.0
stage-packages:
- libicu70
apps:
whatime:
command: Whatime
Metadata
The snapcraft.yaml file starts with a small amount of human-readable metadata, which usually can be lifted from the GitHub description of the project README.md. This data is used in the presentation of your app in the Snap Store.
name: whatime
version: '1.0.0'
grade: devel
summary: Get the current time in various cities around the world
description: |
Whatime is able to get you the current time in several different cities
around the world.
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.
The version is a user facing version to be displayed. You can also specify git for the version, which will use the current git tag or commit as the version string. Versions carry no semantic meaning in snaps.
The grade is an optional key that defines the quality grade of the snap. If can be either devel, which means it’s a development version of the snap, so not to be published to the stable or candidate channels, or stable, which can be released to all channels.
The summary can not exceed 79 characters. You can use the pipe symbol ‘|’ in the description key to declare a multi-line description.
Base
The base keyword declares which base snap to use with your project. A base snap is a special kind of snap that provides a run-time environment alongside a minimal set of libraries that are common to most applications.
base: core22
As used above, core22 is based on Ubuntu 22.04 LTS. See Base snaps for more details.
Security model
The next section describes the level of confinement applied to your app.
confinement: devmode
Snaps are containerized to ensure more predictable application behaviour and greater security. Unlike other container systems, the shape of this confinement can be changed through a set of interfaces. These are declarations that tell the system to give permission for a specific task, such as accessing a webcam or binding to a network port.
It’s best to start a snap with the confinement in warning mode, rather than strictly applied. This is indicated through the devmode keyword. When a snap is in devmode, runtime confinement violations will be allowed but reported. These can be reviewed by running journalctl -xe.
Because devmode is only intended for development, snaps must be set to strict confinement before they can be published as “stable” in the Snap Store. Once an app is working well in devmode, you can review confinement violations, add appropriate interfaces, and switch to strict confinement.
The above example will also work if you change devmode to strict, as you would before a release.
Parts
Parts define what sources are needed to assemble your app. Parts can be anything: programs, libraries, or other needed assets, but for now, we’re only going to use one part: the whatime source code in the local directory. In other cases, these can point to remote git repositories or tarballs.
parts:
whatime:
plugin: dotnet
dotnet-build-configuration: Release
dotnet-self-contained-runtime-identifier: linux-x64
source: .
build-packages:
- dotnet-sdk-6.0
stage-packages:
- libicu70
The dotnet plugin can be used in .NET projects to install dependencies via the NuGet package manager, compile the application, and publish it. Optionally, the following parameters can also be defined:
-
dotnet-build-configuration: The .NET build configuration to use. Defaults to Release. -
dotnet-self-contained-runtime-identifier: Optional parameter to specify the runtime identifier to use when building a self-contained application. Setting this parameter will automatically trigger a self-contained build (with the--self-containedflag on thedotnet publishcommand).
The output of the deployment should contain the executable file along with all the necessary DLLs and dependencies necessary to run it. If you want to deploy your application as a single-file executable, you should set the following parameter inside the .csproj file of your project:
<PropertyGroup>
…
<PublishSingleFile>true</PublishSingleFile>
</PropertyGroup>
By doing this, the parameter dotnet-self-contained-runtime-identifier becomes required, since a runtime identifier is required to build a single-file .NET executable.
The source should point to the root of your .NET project. In our case, it points to the local directory as it’s where the source tree is located. It can also point to a URL if the source code is available as a compressed archive or a revision control repository.
You should also use build-packages to list any required package during build time. We are listing the dotnet-sdk-6.0 package as it installs the .NET 6 SDK, which is required by the plugin and does not get installed automatically.
The stage-packages directive is used to list any required packages during run time. In our case, the libicu70 is a required system package to run the .NET application.
Apps
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 full path to the binary to be run. This is resolved relative to the root of your snap contents.
apps:
whatime:
command: Whatime
If your command name matches the snap name, users will be able to run the command directly. If the names differ, then apps are prefixed with the snap name (whatime.command-name, for example). This is to avoid conflicting with apps defined by other installed snaps.
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/mateusrodrigues/whatime.git
After you’ve created the snapcraft.yaml (which already exists in the above repository), you can build the snap by simply executing the snapcraft command in the project directory:
$ snapcraft
Launching instance…
Executed: pull whatime
Executed: overlay whatime
Executed: build whatime
Executed: stage whatime
Executed: prime whatime
Executed parts lifecycle
Generated snap metadata
Created snap package whatime_1.0.0_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 whatime_1.0.0_amd64.snap --devmode --dangerous
You can then try it out:
$ whatime --help
Removing the snap is simple too:
$ sudo snap remove whatime
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 mydotnetapp
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 mydotnetapp_*.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 .NET snap. For a more in-depth overview of the snap building process, see Creating a snap.