Go applications

Go makes it easy to create a zip of your app that runs across Linux, without dependencies. However, end user discovery and update management remain a challenge. Snaps fill this gap, letting you distribute a Go app in an app store experience for end users.

Why are snaps good for Go projects?

Installing Go applications often consists of downloading pre-built binaries (or running go get). When distributed this way, getting updates is an exercise left to the reader. With snapcraft it’s just one command to produce a bundle that works anywhere and can be automatically updated.

Here are some snap advantages that will benefit many Go projects:

  • Snaps are easy to discover and install
    Install with snap install mygoapp, regardless of distribution.
  • Snaps automatically update to the latest version
    Four times a day, users’ systems will check for new versions and upgrade in the background.
  • Extremely simple daemon creation
    A single snap can provide multiple applications and services.
  • Deliver assets with your snap
    Include images and static web content inside the package.

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 Go 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 existing project, HTTPLab. Don’t worry, we’ll break this down.

name: test-httplab
version: git
summary: An interactive web server.
description: |
  HTTPLab let you inspect HTTP requests and forge responses.
confinement: devmode
base: core18
parts:
  test-httplab:
    plugin: go
    go-importpath: github.com/gchaincl/httplab
    source: .
    source-type: git
    build-packages:
      - gcc
apps:
  test-httplab:
    command: bin/httplab

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-httplab
version: git
summary: An interactive web server.
description: |
  HTTPLab let you inspect HTTP requests and forge responses.

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.

By specifying git for the version, the current git tag or commit will be used as the version string. Versions carry no semantic meaning in snaps.

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

The next section describes the level of confinement applied to your app.

confinement: devmode

Snaps are containerised 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.

Parts

Parts define what sources are needed to assemble your app. Parts can be anything: programs, libraries, or other needed assets.
In this case we have one: the httplab source code. In other cases, these can point to local directories, remote git repositories, or tarballs.

The Go plugin will build using the version of Go on the system running snapcraft.

When using local sources, snapcraft needs to construct a suitable GOPATH. For this it uses go-importpath to know where the sources should live within GOPATH/src.

parts:
  test-httplab:
    plugin: go
    go-importpath: github.com/gchaincl/httplab
    source: .
    source-type: git
    build-packages:
      - gcc

For more details on Go-specific metadata, see The go plugin.

Apps

Apps are the commands and services exposed to end users. 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 (httplab.command-name, for example). This is to avoid conflicting with apps defined by other installed snaps.

If you don’t want your command prefixed you can request an alias for it on the Snapcraft forum. These are set up automatically when your snap is installed from the Snap Store.

apps:
  test-httplab:
    command: bin/httplab

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.

Building the snap

You can download the example repository with the following command:

$ git clone https://github.com/snapcraft-docs/httplab

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-httplab_v0.0.1+git74.a92fbb7-dirty_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-httplab_*.snap --devmode --dangerous

You can then try it out:

$ test-httplab -h

Removing the snap is simple too:

$ sudo snap remove test-httplab

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 mygosnap

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 mygosnap_*.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 Go snap. For a more in-depth overview of the snap building process, see Creating a snap.

Last updated 4 months ago. Help improve this document in the forum.