• Thousands of remote devices
• Full of sensors
• Remote command, local interactions

• Manage devices
  • Inventory
  • Register new devices
  • Push upgrades

• Manage devices
  • Inventory
  • Register new devices
  • Push upgrades
• Monitor
  • Record events/updates from devices
  • Detect issues, lost devices, ...

• Manage devices
  • Inventory
  • Register new devices
  • Push upgrades
• Monitor
  • Record events/updates from devices
  • Detect issues, lost devices, ...
• Actually use the devices
  • Aggregate information for end users
  • Transform user requests into commands

• Seldom changes
• Lots of data: model, manufacturer, serial number, mac addresses, ...
• Including components and subcomponents

class KioskModel(models.Model):
    """A version of our kiosks."""
    reference = models.SlugField(max_length=16)
    commercial_name = models.CharField(max_length=32)

    manufacturer = models.ForeignKey(Manufacturer)
    family = models.ForeignKey(KioskFamily)

class KioskModel(models.Model):
    """A version of our kiosks."""
    reference = models.SlugField(max_length=16)
    commercial_name = models.CharField(max_length=32)

    manufacturer = models.ForeignKey(Manufacturer)
    family = models.ForeignKey(KioskFamily)

class Kiosk(models.Model):
    """One specific kiosk."""
    kiosk_model = models.ForeignKey(KioskModel)
    firmware_version = models.ForeignKey(FirmwareVersion)

    customer = models.ForeignKey(Customer)
    location = models.ForeignKey(InstallationSite)
    notes = models.TextField()

Get all the Django goodness:

• Simple admin interface
• New fields? django.db.migrations helps a lot
• Django apps for history tracking, analysis, reporting...
• Use APIs (with the excellent django-rest-framework) for automatic inventory updates

Embedded systems specifics:

• Registering inventory at the factory or by the device?
• Pushing upgrades

Embedded systems specifics:

• Registering inventory at the factory or by the device?
• Pushing upgrades

Security:

• Ensuring the inventory update comes from the right device
• Checking that all data comes unaltered

=> Some problems might be better solved by dedicated tools (salt, ...)

Critical for operations:

• A device crashed, why?
• Does the latest firmware perform better/worse?
• The only way to get a view of the real world your devices live in

=> Monitoring will be a huge part of your network traffic.

One update every five minutes, for 3000 devices, means 10 updates per second...

• With PostgreSQL, Django can handle great amounts of data (think 100 000 000 lines!)
• Beyond, use dedicated storage engines (e.g elastic)
• Interface through Django to build reports mixing inventory and monitoring data

In a distributed system:

• You will lose messages
• Some messages might arrive late
• Don't forget to synchronize devices' clocks

Tips

• Send the full state of the device in each message, even when triggered by a specific event
• Send the time since last change for simple binary (on/off) sensors
• Keep a cache of the "last known state" in Django's DB even if the archives are elsewhere

Where using Django really helps!

Publish data to users:

• Maybe aggregated from various devices
• Multi-devices: users expect the data on a website, in their app, ...

Send commands to devices:

• On user input
• In reaction to other events
• From your operation center

Single logic for all requests:

# app/processes.py
def reserve(user, charge_point):
    if charge_point.seen_recently and charge_point.unused:
        user.reservations.create(charge_point=charge_point)
        charge_point.set_color('blue')

Single logic for all requests:

# app/processes.py
def reserve(user, charge_point):
    if charge_point.seen_recently and charge_point.unused:
        user.reservations.create(charge_point=charge_point)
        charge_point.set_color('blue')

# app/views/customer.py
def reserve(request):
    # ...
    if form.is_valid():
        processes.reserve(form.customer, form.charge_point)

Single logic for all requests:

# app/processes.py
def reserve(user, charge_point):
    if charge_point.seen_recently and charge_point.unused:
        user.reservations.create(charge_point=charge_point)
        charge_point.set_color('blue')

# app/views/customer.py
def reserve(request):
    # ...
    if form.is_valid():
        processes.reserve(form.customer, form.charge_point)

# ws/charge_point.py
def on_card_swipe(charge_point, card):
    if card.is_active():
        processes.reserve(card.owner, charge_point)

• Network latency, NATs: you can't directly send a command as part of a Django request
• "Split brain effect"
  • The datacenter only has a partial view of the world
  • The device itself only knows what its sensors show
  • What if sensors malfunction?

• Twitter: @raphaelbarrois
• https://github.com/rbarrois
• Xelnor @ irc.freenode.net