Equivalent of systemd's template services?

snapcraft
1

I’ve created a Snap package for noVNC, which is a web interface and client for VNC. So for example if your VNC server runs on port 5901 on your machine you could run an instance of novnc that listens on port 6081 and connects to that VNC server on port 5901:
/snap/bin/novnc --vnc localhost:5901 --listen 6081

The issue is that I can’t see any good way to make this a ‘service’. I’d like something like systemd’s service templates (https://fedoramagazine.org/systemd-template-unit-files/) so that the user can run something like:
systemctl start novnc@localhost5901

But I don’t see a way to do this using Snap?

2

The Snap (including my attempt at creating services, which is just hard coding the most commonly-used port combinations):

name: novnc
base: core18 # the base snap is the execution environment for this snap
version: '1.1.0'
summary: Open Source VNC client using HTML5 (WebSockets, Canvas)
description: |
  Open Source VNC client using HTML5 (WebSockets, Canvas).
  noVNC is both a VNC client JavaScript library as well as an application built on top of that library. noVNC runs well in any modern browser including mobile browsers (iOS and Android).

grade: stable
confinement: strict

parts:
    novnc:
        source: https://github.com/novnc/noVNC.git #https://github.com/novnc/noVNC/archive/v$SNAPCRAFT_PROJECT_VERSION.tar.gz
        plugin: dump
        stage-packages:
            - websockify
apps:
    novnc:
        command: utils/launch.sh
        plugs: [network, network-bind]
    n5900:
        command: utils/launch.sh --vnc localhost:5900 --listen 6080
        daemon: simple
        plugs: [network, network-bind]
    n5901:
        command: utils/launch.sh --vnc localhost:5901 --listen 6081
        daemon: simple
        plugs: [network, network-bind]
    n5902:
        command: utils/launch.sh --vnc localhost:5902 --listen 6082
        daemon: simple
        plugs: [network, network-bind]
    n5903:
        command: utils/launch.sh --vnc localhost:5903 --listen 6083
        daemon: simple
        plugs: [network, network-bind]
    n5904:
        command: utils/launch.sh --vnc localhost:5904 --listen 6084
        daemon: simple
        plugs: [network, network-bind]
    n5905:
        command: utils/launch.sh --vnc localhost:5905 --listen 6085
        daemon: simple
        plugs: [network, network-bind]
3

Hello, to configure a snap service you’ll have to use the snap configuration options and configure hook, check out https://docs.snapcraft.io/configuration-in-snaps/510 and https://docs.snapcraft.io/supported-snap-hooks/3795#heading--the-configure-hook for more details.

You can check out the uhttpd snap for an implementation: