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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Reference