==============
Microservices
==============

1) Monolith Architecture
2) Drawbacks of Monolithic
3) Microservices Architecture
4) Pros & Cons with Microservices

5) Service Registry (Eureka)
6) Admin Server
7) Zipkin Server
8) FeignClient (Interservice Comm)
9) Load Balancer (Ribbon)
10) API Gateway (Filters + Routing)
11) Config Server
12) Circuit Breaker (Resillence4J)


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Monolith Architecture
======================

=> Developing all functionalities in single application.

1) Presentation Layer
2) Business Layer
3) Data Access Layer

=> Drawbacks with Monolith Architecture

	1) Burden on server

	2) Response Delay

	3) Single Point Of Failure

	4) Technology Dependent

	5) Re-Deploy entire app

=> To overcome problems of Monolith Architecture, people are using Microservices Architecture.

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Microservices	
===============

=> It is not a new technology

=> It is not a framework

=> It is not a library

=> It is an architectural design pattern.

=> It is universal and anyone can use this architecture to develop applications.	

Note: The main aim of microservices design pattern is to develop application functionalities with loosely coupling.

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Advantages with Microservices
==============================

1) Loosely Coupled

2) Burden Reduced on Servers

3) Easy Maintence

4) No Single point of failure

5) Technology Independent

6) Quick deliveries


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Challenges with Microservices
==============================

1) Bounded Context

2) Repeated configurations

3) Visibility

=> Bounded context means identifying how many microservices we need to develop for one application and deciding which functionality we need to add in which microservice.

=> In Several microserices we need to write same configurations like data source, smtp, kafka, redis etc.

=> In microservice architecture we might not get chance to work with all apis in the application.

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Spring Cloud with Microservices
=================================

1) Service Registry (Eureka)
2) Admin Server
3) Zipkin Server
4) Config Server
5) Kafka Server
6) Redis Server
7) API Gateway
8) FeignClient (Interservice communication)



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Service Registry
==================

=> It is also called as Service Discovery or Discovery server

=> Service Registry is used to maintain all Microservices (apis) information like name, status, url, no.of instances and health at once place.

=> It will provide user interface to get apis info.

=> We can use Eureka Server as service registry.

Note: Eureka Server provided by Spring Cloud Libraries.

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Admin Server
=============

=> It is used to monitor and manage all the apis at one place

Ex: health, info, beans, url-mappings, env, loggers, thread dump, heap dump...

=> It provides beautiful user interface to access all apis actuator endpoints at one place.

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Zipkin Server
==============

=> It is used for distributed tracing of our requests

ex: 

1) Which request processed by which microservice

2) Time taken to process a request

3) How many microservices involved in request processing

=> It provides beautiful user interface to trace microservices request processing details.


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Config Server
================

=> It is used to externalize config props of our application.

Note: Instead of keeping properties (datasource, smtp, kafka, redis...) in our application we can load them from git repo using config server.

=> Config Server makes our application loosely coupled with properties file or yml file.

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FeignClient
============

=> It is used for interservice communication

=> If one api communicate with another api with in the same application then it is called as Inter service communication.


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Kafka Server
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=> It is used as message broker

=> Distributed streaming platform

=> It is used to process realtime data feeds

=> It works based on publisher-subscriber model

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Redis Server
===============

=> Redis is a cache server

=> Redis we can use as in memory database

=> Redis represents data in key-value format

=> Redis is used to reduce no.of db calls and improve performance of the application.

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API Gateway
=============

=> It acts as Entry point for all backend apis.

=> It acts mediator between frontend app and backend apis.

=> In API Gateway we will write filters + Routings

		Filter : We can perform pre-process & post-process

		Routings : To forward request to particular backend-api.