This document discusses Snaps, a packaging format for Linux applications that provides confinement and versioning. It begins by explaining the architecture of Snaps and how they isolate applications and provide writable areas. It then demonstrates how to build, install, and update Snaps. It also shows how to create a more complex Snap that includes both a backend service and website. The document guides the reader through cloning the source code, defining the Snap metadata, and building parts for the backend, assets, and website. It explains how to expose the command line interface and web service.

1. Snaps: from Zero to Hero
Dal pacchetto, all’immagine
Marco Trevisan
marco@ubuntu.com
CC BY-SA 3.0

2. classic
kernel
snappy
os
appapp
kernel config
os writable files
app writable
area
app writable
areaany package can
write to any file
read-only
snaps
writable
spaces
per snap
filesystem

3. versioned root writable area
(for services)
$SNAP_DATA
common root writable area
(for services)
$SNAP_COMMON
versioned user writable area
$SNAP_USER_DATA
/tmp (per service and
app)/tmp (per service and
app)
/tmp
(per service and app
process)
snap code & assets
(squashfs, RO bind-mounted in /snap/<snap_name>/<version>)
$SNAP
Service
common user writable area
$SNAP_USER_COMMON
Service CLI GUI

4. versioned root writable area
(for services)
$SNAP_DATA
common root writable area
(for services)
$SNAP_COMMON
versioned user writable area
$SNAP_USER_DATA
/tmp (per service and
app)/tmp (per service and
app)
/tmp
(per service and app
process)
~
/dev/<device>
/sys
/
(from
core snap)
/var/lib/snapd/hostfs
(/ from host)
snap code & assets
(squashfs, RO bind-mounted in /snap/<snap_name>/<version>)
$SNAP
Service
common user writable area
$SNAP_USER_COMMON
Service CLI GUI

5. Interazione tra snap
app snapapp snap
app writable
area
app writable
area
Le app sono confinate ed isolate
app snap
app writable
area
app snap
app writable
area

6. Ubuntu Core: un sistema all-snaps!
Ed un sistema moderno per creare distribuzioni
Kernel snap
Core snap
Gadget snap
App snap
App snap
App snap
Content interface snap
● Integrità assicurata da un sistema in sola lettura squashfs
● Non serve riflashare tutto quando cambia un componente

7. alla prova di snapd

8. Minimum system requirements
Processor Architecture
x86 or ARMv7+ (Cortex-A7 single core)
Memory
256MB
Flash Storage
512MB storage
Available Connectivity types
WiFi, Ethernet, USB, BT4.0 BLE, ..

9. # Prerequisito: installa snapd nel sistema
# O usa un immagine per KVM di Ubuntu-core
# http://snapcraft.io
# Installa ed esegui il tuo primo snap
$ snap find hello
$ sudo snap install hello
$ hello
$ snap list
# Snap può fornire servizi e diversi binari
$ hello
$ hello.universe

10. # Aggiorna gli snap nel sistema (automatico)
$ sudo snap refresh
# Passa alla versione di “hello” di un altro
# canale
$ sudo snap refresh hello --beta
$ hello
# Rimuove uno snap
$ sudo snap remove hello

11. # Uno snap più complesso!
$ sudo snap install face-detection-demo --devmode
--beta
# Apri http://localhost:8080 (service).
# Attiva la webcam via web o da:
$ face-detection-demo --enable-camera
# Il comando comunica (via Unix socket)
# col servizio, che è collegato alla webcam
# ed in ascolto sulla rete.
# Utilizza le altre opzioni, disponibili anche
# nell’interfaccia web

12. # Aggiorna all’ultima versione dell’app!
$ sudo snap refresh face-detection-demo --devmode --edge
# L’interfaccia web non funziona più,
# ed i dati son stati eliminati!
# facciamo il revert per recuperare servizio (e dati!):
$ sudo snap revert face-detection-demo --devmode
# La versione è blacklisted, non viene riscaricata
$ sudo snap refresh face-detection-demo --devmode --edge
$ sudo snap remove face-detection-demo

13. Build your first snap

14. Build snaps on classic, deploy on Ubuntu Core

15. https://tutorials.ubuntu.com/
create-first-snap
build-a-nodejs-service

16. # Creating this first (non trivial) snap!
# Ensure you have snapcraft installed
$ sudo apt install snapcraft
# Clone our source code
$ git clone
https://github.com/ubuntu/face-detection-demo
--branch vanilla
# Hint: snapcraft.yaml is available at
http://bit.ly/2d9UOKH

17. # Creazione metadata
$ cd face-detection-demo
$ snapcraft init
# Apri e modifica lo snapcraft.yaml:
name: face-detection-demo
version: ‘1.0’
summary: Demo for Face Detection statistics
description: |
This demo shows face detection statistics
with fun heads.
grade: devel
confinement: devmode

18. # Adding golang part
parts:
face-detection-backend:
source: .
plugin: go
go-importpath: github.com/ubuntu/face-detection-demo
build-packages:
- build-essential
- libopencv-dev

19. # Shipping backend assets
parts:
face-detection-backend:
[…]
assets-backend:
source: .
plugin: dump
snap: [images, frontfacedetection.xml]

20. # And finally, the website part!
parts:
face-detection-backend:
[…]
assets-backend:
[…]
website:
source: https://github.com/ubuntu/face-detection-web.git
plugin: bower
organize:
‘*’: ‘www/’

21. # First build and install
$ snapcraft
$ sudo snap install *.snap --devmode
# No http://localhost:8080 service or
face-detection-demo CLI!
-> We need to expose them explicitly

22. # Exposing a command and a service:
apps:
tool:
command: face-detection-cli
service:
command: face-detection-service
daemon: simple
restart-condition: always
# Rebuild, reinstall and profit!
$ snapcraft
$ sudo snap install *.snap --devmode
$ face-detection-demo.tool --help

23. # Simplifying command name:
apps:
face-detection-demo:
command: face-detection-cli
service:
[…]
# Rebuild, reinstall and check the new command
name!
$ snapcraft
$ sudo snap install *.snap --devmode
$ face-detection-demo --help
# Head over to http://localhost:8080

24. snapcraft.io/
developer.ubuntu.com/en/snappy
github.com/snapcore/snapd
github.com/snapcore/snapcraft
sudo snap install snap-codelabs
# http://localhost:8123