Introduction

I’ve recently published a few snaps of various Node.js projects. So I was encouraged to write a tutorial on building snaps out of Node.js projects. This tutorial will detail how to get setup with necessary tools, go over the snapcraft.yaml format, explain how to build a snap of a Node.js project, and detail how to publish that snap to the Ubuntu snap store.

Prerequisites

To get started snapping Node.js modules you’ll need to have snapd and snapcraft installed. snapd will include the snap command that will allow you to search and install snaps from the store. snapd is available on many different Linux distributions, but if you are using Ubuntu 16.04 or greater you can just run:

sudo apt install snapd

snapcraft is a tool for creating and building snap packages. Installing snapcraft on Ubuntu is as simple as:

sudo apt install snapcraft

If you are also developing the Node module to be packaged, you’ll want to have node and npm installed. Covering that is outside the scope of this tutorial. You can find more info on the Node.js website.

snapcraft.yaml

Defining how a snap is built is a simple YAML file called snapcraft.yaml. The yaml file contains all the necessary pieces to build a snap.

name: hello-node-snap
version: "1.0.0"
summary: A simple hello world command
description: A command that simply prints hello world.
confinement: strict

apps:
  hello-node-snap:
    command: bin/hello-node-snap
    plugs: [network]

parts:
  hello-node-snap:
    plugin: nodejs
    node-packages:
      - hello-node-snap

You can find this snapcraft.yaml and the rest of the hello-node-snap example on GitHub. This file is fairly small and easily understood, so I’ll break the file down into chunks to expand upon each section.

name: hello-node-snap
version: "1.0.0"
summary: A simple hello world command
description: A command that simply prints hello world.

The first part of the snap is all the human friendly portions. The name, version, summary, and description are used in the snap store to help users find your app. The summary should be a very short description of your app, and is limited to only 78 characters. The description should be more verbose so that users can make an informed choice when installing your snap.

confinement: strict

The next section is the confinement of your app. This may be either strict or devmode. Strict means that it will run under full confinement and will not be able to access parts of the host system that are outside of its boundaries. When in devmode a snap will have full access to the underlying system. It is not recommend to distribute an app with devmode confinement, but devmode can be very useful for developing your snap.

apps:
  hello-node-snap:
    command: bin/hello-node-snap
    plugs: [network]

The apps section is a list of commands or daemons that this snap exposes. This snap exposes one command hello-node-snap. This is how users will be able to run your app. Underneath the hello-node-snap app is the command, which is the path to the command to run. This is relative to the root of the snap.

After the command is the plugs section. The plugs section is a list of interfaces that allow a command to access shared resources on the host machine. They could be loosely thought of as permissions. A list of common and reserved interfaces can be found in the snapcraft documentation. In this example we are requesting access to the network. network is for accessing the network as a client. On the other hand, you may need network-bind if you want to set up a server. Another common interface is the home interface, which grants you access to a users home directory.

Note: Network access is not actually needed for this tutorial, but it is there to show how to use the interfaces.

parts:
  hello-node-snap:
    plugin: nodejs
    node-packages:
      - hello-node-snap

The final part of our snapcraft.yaml file is the parts section. Parts define how your app is built and from what sources. You can mix and match parts as needed, but for a Node.js snap you may only need one part. The hello-node-snap part uses the nodejs plugin. This plugin will tell snapcraft to download a version of Node.js and any modules you specify for inclusion in your snap (listed under node-packages). For this tutorial we only need one node module, the hello-node-snap module (created specifically for this tutorial).

If you require a specific version of Node.js for your snap, you can do so by adding node-engine to your part. node-engine is a string of the version you require.

If your Node module requires or depends on non-pure JavaScript modules and needs to be compiled, you’ll want to add:

build-packages:
  - python
  - build-essential

And any other necessary packages (these are the names of Ubuntu packages in apt).

For more information about the different available parts, check out the snapcraft plugin documentation.

Building the Snap

Now that we have a snapcraft.yaml setup, we can use snapcraft to package our new snap. From within the same directory as the snapcraft.yaml, run:

snapcraft

Snapcraft will run through different steps preparing your snap package. When it completes you’ll be greeted with a shiny new snap, and in the case of this tutorial the snap will be called hello-node-snap_1.0.0_amd64.snap.

To test your snap locally before you upload it to the store (and I cannot stress enough the importance of testing your snaps locally), you can run:

sudo snap install hello-node-snap_1.0.0_amd64.snap

If you already have the package installed you may need to remove the old snap by running:

sudo snap remove hello-node-snap

Now that the snap is installed you can run our hello world command:

hello-node-snap

Now that you have a working step it is time to publish it to the store. But before publishing your snap, it is recommended to run:

snapcraft cleanbuild

This command builds the snap in a clean LXC container. Doing so can help you catch any issues with missing build-packages and the like.

Publishing the Snap

In order to publish a snap to the Ubuntu store you need to log in to both snapcraft and snap with your myapps.developer.ubuntu.com account.

snapcraft login
snap login [email protected]

In order to publish your snap you need to register a snap name, you can do this on myapps or via the command line:

snapcraft register hello-node-snap

When the upload finishes, you can then visit myapps to finalize any details before publishing your snap to the store. An important thing to add is a support url, in case users run into any issues using your snap. You need to set your snap channels by clicking on the latest release (since this is the first upload it will be #1). Then click the “Edit” button next to “Channels”. For an explanation of the different channels, check out this guide to publishing snaps.

After you square away the details of your snap, click the “Publish your application” button to publish it to the store. Now you can find your snap and install it with snapd:

sudo snap find hello
sudo snap install hello-node-snap

After a short while your new snap will show up on uApp Explorer. And you have successfully published a snap!

Conclusion

I hope that you have found this tutorial useful. If you have any feedback you can submit an issue to the hello-node-snap GitHub repo or contact me via my website.

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