Node

Node has rich tools for packaging, distributing and sandboxing applications. Snapcraft builds on top of these familiar tools such as npm and yarn to create snaps.

What problems do snaps solve for Node applications?

Often Linux install documentation for Node applications is complicated, requiring software to be installed via apt, rpm and npm or care taken to run with the right version of Node. With snapcraft it’s just one command to produce a bundle that works anywhere.

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

  • Bundle all the runtime requirements, including the exact versions of system libraries.
  • Simplify installation instructions, regardless of distribution, to snap install mynodeapp.
  • Directly control the delivery of automatic application updates.
  • Extremely simple creation of services.

How long will this guide take to complete?

Typically this guide will take around 20 minutes and will result in a working Node app in a snap. Once complete, you’ll understand how to package Node applications as snaps and deliver them to millions of Linux users. After making the snap available in the store, you’ll get access to installation metrics and tools to directly manage the delvery of updates to Linux users.

Getting started

By way of an example, let’s take a look at how a snap is created for the wethr app.

wethr

Snaps are defined in a single yaml file placed in the root of your project. The wethr example shows the entire snapcraft.yaml for an existing project, leveraging the existing package.json to satisfy runtime requirements. We’ll break this down.

name: wethr
version: git
summary: Command line weather tool.
description: |
  Get current weather:-
    $ wethr
  Get current weather in metric units
    $ wethr --metric
  Get current weather in imperial units
    $ wethr --imperial

grade: devel
confinement: devmode

apps:
  wethr:
    command: wethr

parts:
  wethr:
    plugin: nodejs
    source: .

Metadata

The snapcraft.yaml 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. The summary: can not exceed 79 characters. You can use a pipe in the description: key to declare a multi-line description.

name: wethr
version: git
summary: Command line weather tool.
description: |
  Get current weather:-
    $ wethr
  Get current weather in metric units
    $ wethr --metric
  Get current weather in imperial units
    $ wethr --imperial

Confinement

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: the wethr source code. In other cases these can point to local directories, remote git repositories, or tarballs.

The Node plugin will also bundle Node in the snap, so you can be sure that the version of Node you test against is included with your app. Dependencies from your package.json will also be bundled.

parts:
  wethr:
    plugin: nodejs
    source: .

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 (wethr.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:
  wethr:
    command: wethr

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’ll first need to install snap support, and then install the snapcraft tool:

sudo snap install --beta --classic snapcraft

If you have just installed snap support, start a new shell so your PATH is updated to include /snap/bin. You can then build this example yourself:

git clone https://github.com/snapcraft-docs/wethr
cd wethr
snapcraft

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 wethr_*.snap --devmode --dangerous

You can then try running wethr.

wethr

Removing the snap is simple too:

sudo snap remove wethr

Share with your friends

To share your snaps you need to publish them in the Snap Store. First, create an account on the dashboard. Here you can customize 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.

snapcraft register mynodesnap

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 mynodesnap_*.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.

Further customisations

Here are all the Node plugin-specific keywords:

    - node-packages:
      (list)
      A list of dependencies to fetch using npm.
    - node-engine:
      (string)
      The version of nodejs you want the snap to run on.
    - npm-run:
      (list)
      A list of targets to `npm run`.
      These targets will be run in order, after `npm install`
    - node-package-manager
      (string; default: npm)
      The language package manager to use to drive installation
      of node packages. Can be either `npm` (default) or `yarn`.

You can view them locally by running:

snapcraft help nodejs

Extending and overriding behaviour

You can extend the behaviour of any part in your snapcraft.yaml with shell commands. These can be run after pulling the source code but before building by using the prepare keyword. The build process can be overridden entirely using the build keyword and shell commands. The install keyword is used to run shell commands after building your code, useful for making post build modifications such as relocating build assets.

Using the wethr example above, we can run the test suite at the end of the build. If this fails, the snap creation will be terminated:

parts:
  wethr:
    plugin: nodejs
    source: .
    install: |
      npm test