IoT Physical Servers and Cloud Offerings.pdf

Unit - V
IoT Physical Servers &
Cloud Offerings
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Outline
• Introduction to Cloud Storage models
• Communication APIs
• Webserver-Web server for IoT
• Cloud for IoT
• Python web application framework
• Designing a RESTful web API.
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Introduction to Cloud Computing
• The Internet of Things (IoT) involves the internet-connected devices which are used
to perform the processes and services that supports way of life.
• Another component set to help IoT succeed is cloud computing, which acts as a sort
of front end.
• Cloud computing is an increasingly popular service that offers several advantages to
IOT, and is based on the concept of allowing users to perform normal computing
tasks using services delivered entirely over the internet.
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• In simple words, Cloud Computing means providing computing services over the
internet (called as cloud).
• The computing services include Servers, Software, Storage, Database,
Networking, Analytics, Intelligence etc.,
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• A worker may need to finish a major project that must be submitted to a manager,
but perhaps they encounter problems with memory or space constraints on their
computing device.
• Memory and space constraints can be minimized if an application is instead hosted
on the internet.
• The worker can use a cloud computing service to finish their work because the data is
managed remotely by a server.
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• Another example- you have a problem with your mobile device and you need to
reformat it or reinstall the operating system.
• You can use Google Photos to upload your photos to internet-based storage.
• After the reformat or reinstall, you can then either move the photos back to you
device or you can view the photos on your device from the internet when you want.
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Features of Cloud Computing
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Types of Cloud Computing Storage Services
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Types of Cloud Services
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• Infrastructure-as-a-service(IaaS) provides users the ability to provision computing
and storage resources. These resources are provided to the users as a virtual
machine instances and virtual storage.
• Platform-as-a-Service(PaaS) provides users the ability to develop and deploy
application in cloud using the development tools, APIs, software libraries and
services provided by the cloud service provider.
• Software-as-a-Service(SaaS) provides the user a complete software application or
the user interface to the application itself.

Types of Cloud Services
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Advantages
• Cost
• Speed
• Security
• Scalability
• Reliability
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Cloud Storage API
• A cloud storage API is an application program interface that connects a
locally-based application to a cloud-based storage system, so that a user
can send data to it and access and work with data stored in it.
• To the application, the cloud storage system is just another target device,
like tape or disk-based storage.
• An application program interface (API) is code that allows two software
programs to communicate with each other.
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Cloud Storage API
• The API defines the correct way for a developer to write a program that
requests services from an operating system (OS) or other application.
• APIs are implemented by function calls composed of verbs and nouns.
• The required syntax is described in the documentation of the application
being called.
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How APIs Works
• APIs are made up of two related elements.
• The first is a specification that describes how information is exchanged
between programs, done in the form of a request for processing and a
return of the necessary data.
• The second is a software interface written to that specification and
published in some way for use. The software that wants to access the
features and capabilities of the API is said to call it, and the software that
creates the API is said to publish it.
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Why APIs are important
• The web, software designed exchange information via the internet and
cloud computing have all combined to increase the interest in APIs in
general and services in particular.
• Software that was once custom-developed for a specific purpose is now
often written referencing APIs that provide broadly useful features,
reducing development time and cost and mitigating the risk of errors.
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Why APIs are important
• APIs have steadily improved software quality over the last decade, and the
growing number of web services exposed through APIs by cloud providers
is also encouraging the creation of cloud-specific applications, internet of
things (IoT) efforts and apps to support mobile devices and users.
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Basic Types of APIs
• APIs take three basic forms: local, web-like and program-like.
• Local APIs are the original form, from which the name came. They offer
OS or middleware services to application programs. Microsoft's .NET APIs,
the TAPI (Telephony API) for voice applications, and database access
APIs are examples of the local API form.
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Basic Types of APIs
• Web APIs are designed to represent widely used resources like HTML
pages and are accessed using a simple HTTP protocol. Any web URL
activates a web API.
• Web APIs are often called REST (representational state transfer) or
RESTful because the publisher of REST interfaces doesn't save any data
internally between requests. As such, requests from many users can be
intermingled as they would be on the internet.
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Basic Types of APIs
• Program APIs are based on remote procedure call (RPC) technology that
makes a remote program component appear to be local to the rest of the
software.
• Service oriented architecture (SOA) APIs, such as Microsoft's WS-series of
APIs, are program APIs.
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WAMP - Autobahn for IoT
• Web Application Messaging Protocol (WAMP) is a sub-protocol of Websocket
which provides publish-subscribe and remote procedure call (RPC) messaging
patterns.
• WAMP enables distributed application architectures where the application
components are distributed on multiple nodes and communicate with messaging
patterns provided by WAMP.
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WAMP Session Between Client and Router
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WAMP - Concepts
• Transport: Transport is channel that connects two peers. The default transport
for WAMP is Web socket. WAMP can run over the transports as well which
support message based reliable bi directional communication.
• Session: Session is a conversation between two peers that runs over a
transport.
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WAMP - Concepts
• Client: Clients are peers that can have one or more roles. In publish-subscribe
model client can have following roles:
–Publisher: Publisher publishes events (including payload) to the topic
maintained by the Broker.
–Subscriber: Subscriber subscribes to the topics and receives the events
including the payload.
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WAMP - Concepts
• In RPC model client can have following roles:
–Caller: Caller issues calls to the remote procedures along with call arguments.
–Callee: Callee executes the procedures to which the calls are issued by the caller
and returns the results back to the caller.
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WAMP - Concepts
• Router: Routers are peers that perform generic call and event routing. In publish-
subscribe model Router has the role of a Broker:
–Broker: Broker acts as a router and routes messages published to a topic to all
subscribers subscribed to the topic.
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WAMP Protocol Interaction between the Peers
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WAMP Protocol Interaction between the Peers
• In this protocol, WAMP transport used is Websocket.
• WAMP sessions are established over Websocket transport within the
lifetime of Websocket transport.
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Publish Subscribe Messaging using WAMP -
Autobahn
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Publish Subscribe Messaging using WAMP -
Autobahn
• The client in Publisher role runs a WAMP application component that
publishes messages to the router.
• The router in broker role runs on the server and routes the messages to
the subscribers.
• The router decouples the publisher from the subscribers.
• The communication between publisher- broker and broker subscribers
happens over a WAMP websocket session.
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Commands used for installing Auto Bahn in
Python
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Commands used for installing Auto Bahn in
Python
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WAMP - Autobahn
• Create a WAMP Publisher Component.
• The publisher component will publish a message containing the current
time stamp to a topic named ‘test – topic’.
• Create a WAMP Subscriber component.
• The subscriber component that subscribes to the ‘test-topic’
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WAMP Publisher Component
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WAMP Subscriber Component
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WAMP Subscriber Component
• Run the application router on a websocket server as follows:
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Xively Cloud for IoT
• It is a commercial platform as a service (PAAS) that can be used for
creating solutions for IoT.
• With Xively cloud, IoT developers can focus on the front end infrastructure
and devices for IoT(that generate the data), while the backend data
collection infrastructure is managed by Xively.
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• Xively platform comprises of a message bus for real-time message
management and routing, data services for time series archiving, directory
services that provides a search - able directory of objects and business
services for device provisioning and management.
• Xively provides an extensive support for various languages and platforms
• The Xively libraries leverage standards based API over HTTP, sockets and
MQTT for connecting IoT devices to the Xively Cloud.
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• To start using Xively python library, first we need to register a developer
account and then create development devices on Xively.
• When a new device is created, Xively automatically creates a Feed ID and
an API key to connect to the device.
• Feed ID is a collection of channels or data streams defined for a device
and associated meta data.
• API keys are used to provide different levels of permissions.
• The default API key has read, update, create and delete permissions.
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• Xively devices have one or more channels and each channel enables
bidirectional communication between the IoT devices and Xively cloud.
• IoT devices can send data to a channel using the Xively APIs.
• For each channel one or more triggers can be created. A trigger
specification includes a channel to which the trigger corresponds, trigger
condition and an HTTP post URL to which the request is sent when the
trigger fires.
• Trigger are used to provide integration for third party applications.
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• Let us consider an example of using Xively cloud for an IoT system that
monitors temperature and sends the measurements to a Xively channel.
• Temperature monitoring device can be built by raspberry pi board and a
temperature sensor is connected to the board.
• The raspberry pi runs a controller program that reads the sensor values
every few seconds and sends the measurements to a Xively channel.
• Box 8.4 shows the python program for sending the temperature data to
Xively cloud by using Xively python library.
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• To keep the program simple and without going in to the details of the
temperature sensor, synthetic data is used (generated randomly in
readTemp Sensor()function).
• A feed object is created by providing the API key and Feed ID. Then a
channel named temperature is created.
• The temperature data is sent to this channel in the runController() function
every 10 seconds.
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• Figure 8.6 shows the temperature channel in the Xively dashboard. In this
example a single Xively device with one channel is created. Xively can also
have multiple channels and multiple devices.
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Python Web Application Framework - Django
• Django is an open source web application framework for developing web
applications in Python.
• A "web application framework" in general is a collection of solutions,
packages and best practices that allows development of web
applications and dynamic websites.
• Django is based on the Model-Template-View architecture and provides a
separation of the data model from the business rules and the user
interface.
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Python Web Application Framework - Django
• Django provides a unified API to a database backend.
• Thus web applications built with Django can work with different databases
without requiring any code changes.
• With this fiexibility in web application design combined with the powerful
capabilities of the Python language and the Python ecosystem, Django is best
suited for cloud applications.
• Django consists of an object-relational mapper, a web templating system and
a regular-expression- based URL dispatcher.
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Django Architecture
• Django is Model-Template-View (MTV) framework .
Model
• The model acts as a definition of some stored data and handles the
interactions with the database. In a web application, the data can be
stored in a relational database, non-relational database, an XML file,
etc. A Django model is a Python class that outlines the variables and
methods for a particular type of data.
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Django Architecture
Template
• In a typical Django web application, the template is simply an HTML
page with a few extra placeholders. Django’s template language can
be used to create various forms of text files (XML, email, CSS,
Javascript, CSV, etc.)
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Django Architecture
View
• The view ties the model to the template. The view is where you write the
code that actually generates the web pages. View determines what
data is to be displayed, retrieves the data from the database and passes
the data to the template.
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Starting Development with Django
Creating a Django Project and App
• When a new Django project is created, a number of files are created as
described below
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• A Django can have multiple Apps, where these Apps are used to write the
code that makes website function.
• When a new application is created a new directory for the application is
also created which has a number of files including –
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• Django comes with a built in, light weight web server that can be used for
development purposes.
• When the Django development server is started the default project can be
viewed at the URL: http://localhost:8000.
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Configuring a Database
• Developers have a wide choice of databases that can be used for web
applications including both relational and non relational databases.
• Django provides a unified API for database backend thus giving the
freedom to choose the database.
• Django supports various relational database engines including MySQL,
PostgreSQL, Oracle and SQLite3.
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• Support for non relational data bases such as MongoDB can be added by
installing additional engines (Eg. Django- MongoDB engine for
MkongoDB).
• The first step in setting up a database is to install and configure a
database server.
• After installing the data base, the next step is to specify the database
settings in the setting.py file in the Django project.
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Commands to setup My SQL
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Database setting to use MySQL with a
Django Project
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Defining a Model
• A Model acts as a definition of the data in the database.
• Box 8.10 shows an example of a Django model for TemperatureData
collected by an IoT Device.
• The TemperatureData table in the database is defined as a class in the
Django Model.
• Each class that represents a database table is a subclass of
django.db.models.Model which contains all the functionality that allows
the models to interact with the database.
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Defining a Model
• The TemperatureData class has fields timestamp, temperature, lat and lon
all of which are CharField.
• To sync the models with the database, run the following command:
• >python manage.py syncdb
• When the syncdb command is run for the fist time, it creates all the tables
defined in the Django model in the configured database.
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Django Admin Site
• Django provides an administration system that allows to manage the
website without writing the additional code.
• This “admin” system reads the Django model and provides an interface
that can be used to add content to the site.
• The Django admin site is enabled by adding d jango.contrib.admin and d
jango.contrib.admindocs to the INSTALLED_APPS section in the
settings.py file.
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Django Admin Site
• The admin site also requires URL pattern definitions in the url.py file.
• To define which application models to be editable in the admin interface, a
new file named admin.py is created in the application folder.
•
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Defining a View
• The view contains the logic that glues the model to the template.
• The view determines the data to be displayed in the template, retrieves
the data from the database and passes it to the template.
• Conversely, the view also extracts the data posted in a form in the
template and inserts it in the database.
• Typically, each page in the website has a separate view, which is
basically a python function in the views.py file.
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Defining a View
• Views can also perform additional tasks such as authentication, sending
emails, etc.,
• Box 8.12 shows an example of a Django view for the Weather Station
app.
• This view corresponds to the webpage that displays latest entry in the
TemperatureData table.
• In this view the Django’s built in object-relational mapping API is used to
retrieve the data from the TemperatureData Table.
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Defining a View
• The object- relational mapping API allows the developers to write generic
code for interacting with the database without worrying about the
underlying database engine.
• So the same code for database interactions works with different database
backends.
• A specific python library can be chose to the database backend used (eg.
MySQLdb for MySQL, PyMongo for MongoDB etc.) to write database
backed specific code.
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Defining a View
• In the view shown in Box 8.12, the
TemperatureData.objects.order_by(‘_id’) query returns the latest entry in
the table.
• To retrieve all entries, can use table.objects.all().
• To retrieve specific entries, use table.objects.filter(**Kwargs) to filter out
queries that match the specified condition.
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Defining a View
• To render the retrieved entries in the template, the render_to_response
function is used.
• This function renders a given template with a given context dictionary and
returns an HttpResponse object with that rendered text.
• Box 8.13 shows an alternative view that retrieves data from the Xively
cloud.
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Defining a Template
• A Django Template is typically an HTML file (it can be any sort of text file
such as XML, email, CSS, Java script, CSV etc,).
• Django templates allow separation of the presentation of data from the
actual data by using placeholders and associated logic (Using template
tags).
• A template receives a context from the view and presents the data in
context variables in the placeholders.
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Defining a Template
• Box 8.14 shows an example of a template for the Weather Station app
and the variables containing the retrieved temperature, latitude and
longitude are passed to the template.
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Defining a Template
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Defining a Template
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Defining a Template
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Defining a Template
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Defining the URL Patterns
• URL patterns are a way of mapping the URLs to the views that should
handle the URL requests.
• The URLs requested by the user are matched with the URL patterns and
the view corresponding to the pattern that matches the URL is used to
handle the request.
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• Box 8.15 shows an example of the URL patterns for the Weather Station
Project and the URL patterns are constructed using regular expressions.
• The simplest regular expression (r’ ^ $’) corresponds to the root of the
website or the home page.
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• With the Django models, views, templates and URL patterns defined for
the Django project, the application finally runs with the commands shown
in Box 8.16.
•
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Designing a RESTful Web API
• Django REST framework can be installed as follows:
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• After installing the Django REST framework, create a new Django project
named restfulapi, and then start a new app called myapp, as follows:
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• The REST API allows to create, view, update and delete a collection of
resources where each resource represents a sensor data reading from a
weather monitoring station.
• Box 8.17 shows the Django model for such a station.
• The station model contains four fields – station name, timestamp,
temperature, latitude and longitude
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• Box 8.18 shows the Django views for the REST API.
• ViewSets are used for the views that allows to combine the logic for a set
of related views in a single class.
•
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•
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• Box 8.19 shows the serializers for the REST API.
• Serializers allow complex data (such as querysets and model instances)
to be converted to native python datatypes that can be easily rendered
into JSON, XML or other content types.
• Serializers also provide de-serialization, allowing parsed data to be
converted back into complex types, after first validating the incoming
data.
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• Box 8.20 shows the URL patterns for the REST API.
• Since, ViewSets are used instead of views, it can automatically generate
the URL conf for API, by registering the ViewSets with a router class.
• Routers automatically determining how the URLs for an application
should be mapped to the logic that deals with handling incoming
requests.
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• Box 8.21 shows the settings for the REST API Django project.
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• Box 8.21 shows the settings for the REST API Django project.
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• After creating the station REST API source files, the next step is to setup
the database and then run the Django development web server as
follows:
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• Box 8.22 shows examples of interacting with the Station REST API using
CURL.
• The HTTP POST method is used to create a new resource, GET method
is used to obtain information about a resource, PUT method is used to
update a resource and DELETE method is used to delete a resource.
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