Representational State Transfer (REST) in Cloud Computing

Representational State Transfer (REST)

• APIs are for software components; a way for software to interact with other software.
• Web Services are a set of rules and technologies that enable two or more components on the web to talk to each other.
• Not every API is a web service.
• REST API is a web service.
• REST API is an API that follows the rules of REST specification.
• A web service is defined by rules:

1. How software components will talk?
2. What kind of messages they will send to each other?
3. How requests and responses will be handled?

HTTP and REST

• HTTP is an application layer protocol for sending and receiving messages over a network.
• REST is a specification that dictates how distributed systems on the web should communicate.
• REST is a way to implement and use the HTTP protocol.

REST and Systems of Systems

• SOA focuses on loosely coupled software applications running across different administrative domains, based on common protocols and technologies, such as HTTP and XML.
• SOA is related to early efforts on the architecture style of large scale distributed systems, particularly Representational State Transfer (REST).
• REST still provides an alternative to the complex standard-driven web services technology.
• Used in many Web 2.0 services.
• REST is a software architecture style for distributed systems, particularly distributed hypermedia systems, such as the World Wide Web.

Applications:

• Google, Amazon, Yahoo, Facebook and Twitter

Advantage:

• Simplicity
• Ease of being published and consumed by clients.

A simple REST interaction between user and server in the HTTP specification

REST Principles

The REST architectural style is based on four principles:

1. Resource Identification through URIs
2. Uniform, Constrained Interface
3. Self-Descriptive Message
4. Stateless Interactions

Resource Identification through URIs

• The RESTful web service exposes a set of resources which identify targets of interaction with its clients.
• The key abstraction of information in REST is a resource.
• Any information that can be named can be a resource, such as a document or image or a temporal service.
• A resource is a conceptual mapping to a set of entities.
• Each particular resource is identified by a unique name, or more precisely, a Uniform Resource Identifier (URI).
• URI is of type URL, providing a global addressing space for resources involved in an interaction between components as well as facilitating service discovery.
• The URIs can be bookmarked or exchanged via hyperlinks.
• URIs provide more readability and the potential for advertisement.

Uniform, Constrained Interface

• Interaction with RESTful web services is done via the HTTP standard, client/server cacheable protocol.
• Resources are manipulated using a fixed set of four CRUD (create, read, update, delete) verbs or operations:

1. PUT
2. GET
3. POST
4. DELETE

• PUT creates a new resource.
• The resource can then be destroyed by using DELETE.
• GET retrieves the current state of a resource.
• POST transfers a new state onto a resource.

Self-Descriptive Message

• A REST message includes enough information to describe how to process the message.
• This enables intermediaries to do more with the message without parsing the message contents.
• In REST, resources are decoupled from their representation so that their content can be accessed in a variety of standard formats
• Eg:- HTML, XML, MIME, plain text, PDF, JPEG, JSON, etc.
• REST provides multiple/alternate representations of each resource.
• Metadata about the resource is available and can be used for various purposes.
• Cache control
• Transmission error detection
• Authentication or authorization
• Access control.

Stateless Interactions

• The REST interactions are “stateless”
• The message does not depend on the state of the conversation.
• Stateless communications improve visibility, reliability and increase scalability
• Decrease network performance by increasing the repetitive data

REST - Advantages

• RESTful web services can be considered an alternative to SOAP stack or “big web services
• Simplicity
• Lightweight nature
• Integration with HTTP