Microservices with Spring Boot and Spring Cloud

Microservices with Spring Boot and Spring Cloud

Introduction to Web Services

What is a Web Service?

• Service delivered over the web.
• Software system designed to support interoperable machine-to-machine interaction over a network.

Web Services - 3 Keys:

1. Designed for machine-to-machine(or application-to-application) interaction.
2. Should be interoperable - Not platform dependent. (Application A (Java), Application B(.Net), Application C (PHP)) - Irrespective of their technologies they should be able to talk to the ToDo service.
3. Should allow communication over a network. (Communication should not be bound within a local machine).

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Important questions related to web services

1. How does data exchange between applications take place?

             -----Request------->
   

| Application A |---------------------| WebService |

             <-----Response-------

• Application A is consuming a web service.

2. How can we make web services platform independent?

• The Request and Response of the webservice must be platform independent.
• There are two popular formats for requests and responses.

a. XML

• Extensible Markup Language.

<getCourseDetailsRequest>
<id>Course1</id>
</getCourseDetailsRequest>

b. JSON

• Javascript Object Notation [ { "id": 1, "name": "Even", }, { "id": 2, "name": "Odd", } ]

3. How does the Application A know the format of Request and Response?

• Application A needs to send a request to the web service and once it gets the response it needs to be able to process it.

• Service Definition:

• Every web service offers a service definition
• The service definition would specify:
  i. Request/Response Format - JSON, XML, etc.
  ii. Request Structure
  iii. Response Structure
  iv. Endpoint
  

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Web Services - Key Terminology

1. Request and Response

• Request - Input to the web service.
• Response - Output from a web service.

2. Message Exchange Format

• It is the format of the request and the response.
• XML and JSON

3. Service Provider or Server & Service Consumer or Client

             -----Request------->
   

| Application A |---------------------| WebService |

             <-----Response-------

• Application A wants to consume a service from the web service.
• The Web Service is called the service provider.
• Service provider is the one which hosts the web service.
• The service consumer is the one which is consuming the web service. Application A is the client.

| Java Application | ----------------------> | WebService |
| DotNet Application |-----------|
| PHP Application |-----------|

• In the above example, the java application, the dot net application and the PHP application are all consumers of the web service.

4. Service Definition

• The Service Definition is the contract between the service provider and the service consumers.
• The Service Definition states:
  1. Request/Response Format
  2. Request Structure
  3. Response Structure
  4. Endpoint

5. Transport (HTTP and MQ)

• Transport defines how a service is called - over the web or queue.
• In MQ - use communication over a queue.
  • A service requestor would place a message in a queue.
  • The service provider would be listening on the queue.
  • As soon as there's a request on the queue it would take the request, do the processing of it, create the response from the queue and place it back in the queue.
  • The transport used is the MQ.

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Introduction to SOAP Web Service

• SOAP - Simple Object Access Protocol.

• SOAP defines a specific way of building web services.
• SOAP uses XML for Request and Response exchange format.
• SOAP defines a specific XML request and response structure.
  • It should have a SOAP-ENVELOPE
    • SOAP-ENV: Header
      • Contains meta information like authentication, authorization, signature, etc.
    • SOAP-ENV: Body
      • Real content of the request or response.

• SOAP defines a format for your request and response.
• SOAP does not pose any restrictions on your transport - can either use HTTP or MQ.
• In SOAP, the service definition is typically done using web service definition language (WSDL).
• WSDL Defines:
  1. End point
  2. All operations (CRUD)
  3. Request Structure
  4. Response Structure

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Introduction to RESTful Web Services

• REST - REpresentational State Transfer - coined by Roy Fielding.

• Roy Fielding - developed HTTP protocol.

• RESTful web services try to define services using the different concepts that are already present in HTTP.

Resource - Key Abstraction

• A resource is anything that you would want to expose to the outside world through your application.
• A resource has an URI (Uniform Resource Identifier):

• /user/A/todos/1
• /user/A/todos
• /user/A

• A Resource can have different representations

• XML
• HTML
• JSON

• EXAMPLES

• Create a User - POST /users
• Delete a User - DELETE /users/1
• Get all Users - GET/users
• Get one Users - GET /users/1

• Data Exchange Format:

• No Restriction. JSON is popular.

• Transport

• Only HTTP

• Service Defintion

• No Standard. WADL/ Swagger/...

• WADL - Web Application Definition Language - Format to specify your RESTful Web services.

REST focuses on your resources and how do you perform actions on them making best use of HTTP.

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SOAP vs RESTful Web Services

1. Restrictions vs Architectural Approach

• SOAP - format of XML.
• REST - architectural style.

2. Data Exchange Format

• SOAP - data exchange format is XML (specifically SOAP XML).
• REST - no strict data exchange format - (XML / JSON , etc).

3. Service Definition

• SOAP - uses WSDL (Web Service Definition Language).
• REST - no standard (many - WADL - Web Application Definition Language, Swagger).

4. Transport

• SOAP - poses no restriction (HTTP or Messaging Queue (MQ))
• REST - very specific about making the best use of HTTP protocol.

5. Ease of Implementation

• RESTful web services are easier to implement than SOAP.

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Reference

TroubleShoot Reference