Karan Kaw's Blog

Wednesday, March 10, 2021

Saga distributed transactions
https://docs.microsoft.com/en-us/azure/architecture/reference-architectures/saga/saga
https://vasters.com/archive/Sagas.html

Saga Image
https://docs.microsoft.com/en-us/azure/architecture/reference-architectures/saga/images/choreography-pattern.png

Retry pattern
https://docs.microsoft.com/en-us/azure/architecture/patterns/retry

Microservices using SpringBoot | Full Example
https://www.youtube.com/watch?v=BnknNTN8icw

API Gateway

https://www.youtube.com/watch?v=1vjOv_f9L8I

(Forward)Proxy vs Reverse Proxy
https://www.youtube.com/watch?v=AuINJdBPf8I
(Forward)Proxy vs Reverse Proxy
Requests Going Out Via Proxy -> Forward Proxy
Requests Coming In Via Proxy -> Reverse Proxy
Reverse Proxy - Use cases : Security, Load Balancer , Caching
Forward Proxy - Corporate Control, Logging, Monitoring, Cached Responses

Zuul
API Gateway
Edge Microservice -> Sits at the edge of Microservice Architecture, Very close to user input.
Edge Microservice is also known as API Gateway.
"Zuul" is an implementation of API Gateway.
API Gateway - is a Facade/Abstraction Layer at the very edge of Microservices Architecture ,
which handles incoming Requests

Eureka
Eureka - "Found it" in Ancient Greek
Archimedes said it!!!
Eureka is a Registry and LookUp Service which allows Microservice to know each other

Hystrix
Fault Tolerant Library from Netflix which Implements "Circuit - Breaker" Pattern

<!-- https://mvnrepository.com/artifact/org.springframework.cloud/spring-cloud-starter-hystrix -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-hystrix</artifactId>
    <version>1.4.7.RELEASE</version>
</dependency>

How to configure SpringCloud Zuul – Routing and Filtering using SpringBoot | Java Techie
https://www.youtube.com/watch?v=6aG0xFpeNFw

Nested Transaction - Microsoft SQL Server (MSSQL)

SP - @@TxnCount
Use Try Catch Block SQL
Rollback - Sets @@TRANCOUNT to 0
Commit - decrements @@TRANCOUNT Counter by 1

When Counter becomes Zero, Commit or Rollback actually does take its effect
Actually, No Nested Txn in MSSQL
Only 1 Txn in MSSQL

https://sqlinthewild.co.za/index.php/2015/11/03/a-mess-of-nested-transactions/

OUTPUT Clause (Transact-SQL)

https://docs.microsoft.com/en-us/sql/t-sql/queries/output-clause-transact-sql?view=sql-server-ver15

Hystrix, Zuul, Eureka

"Hystrix" is a circuit-breaker Pattern created by Netflix.

https://techblog.constantcontact.com/software-development/circuit-breakers-and-microservices/

Its basically a fault-tolerance management library from spring

<!-- https://mvnrepository.com/artifact/org.springframework.cloud/spring-cloud-starter-hystrix -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-hystrix</artifactId>
    <version>1.4.7.RELEASE</version>
</dependency>

Spring Cloud Starter Hystrix

Spring Cloud Starter Hystrix (deprecated, please use spring-cloud-starter-netflix-hystrix)

"Zuul" -> API Gateway

"Eureka" -> Service Discovery

Tuesday, March 9, 2021

Microservices -2

Dual Writes: The Unknown Cause of Data Inconsistencies
https://www.youtube.com/watch?v=V08YbM_yvXU

SAGA | Microservices Architecture Patterns | Tech Primers
https://www.youtube.com/watch?v=WnZ7IcaN_JA&t=324s

Do you know Distributed transactions?
https://www.youtube.com/watch?v=S4FnmSeRpAY

What is a Distributed Transaction in Microservices?
https://www.youtube.com/watch?v=H6F4BorD49g
Transactions 2:30
Compensating Edits 6:40
Atomic Clocks 11:50
Event Sourcing 13:30
Mini-Monolith 15:20

Monolith Applications - Distributed Transactions - 2 Phase Commit
Asynchronous Communication, Local Transaction , One Step = One Datastore
Endless Retry Mechanism
Algorithm - Eventual Consistency
SAGA Pattern

Circuit Breaker Pattern

https://techblog.constantcontact.com/software-development/circuit-breakers-and-microservices/

Friday, March 5, 2021

Microservices -1 | Eventual Consistency | Transient Exception | Compensating Transaction|Timeout Retry

Hard Consistency - ACID does not apply to microservices

It may have been applicable via 2 Phase Commit in case of Distributed Transaction but the database was still the same

Now its time for Eventual Consistency

ACID on Local Transactions
Multiple steps in Transaction Boundary - Because its just 1
one fails, all Fails

Distributed Transactions
More than 1 Database

Using Multiple Local Transaction
One is committed, Another Fails
Compensatory Transaction(Workaround Steps) - Not Always a Good Practice
https://www.youtube.com/watch?v=jGJT1FRYGcY
Stale Data - Multiple Write -> Dual Write

Begin Txn
Lock
Mutate
Release Lock (Commit) or Rollback ---- Goto State

https://www.youtube.com/watch?v=pSz0Fpvu2Gk
Older Distributed Transaction or Monolithic Architecture
ACID Principles to Multiple External System
2 Phase Commit - Distributed Transactions - Not a Good Fit for Microservices

Distributed Transaction - how ??
Saga
2 Phase Commit --- -Prepare and Commit --> 2 Phases
Prepare1 -> Prepared1 -> Commit1
Prepare2 -> Prepared2 -> Commit2
Commit1 + Commit2 = Commit ----Txn Cordinator ---> Application

2 Phase Commit - Discouraged in Microservices -- HTTP Slowness, LOCKED Resource , Slow
Co-ordinator Fails ? What Then ?

3 Phase allows any Participant to be a Co-ordinator

2Phase / 3-Phase - biggest drawback is - they have a wrapper aroun TXN -
So its long living and synchronous

2 Phase is Okay for - Simple Monolithic Application
But Microservices is already slow,uses HTTP and now u put 2phase commit , Its worse

Asynchronous -- SAGA
Txn1 -> Message
Txn2 -> Message (If Failure, Then Rollback Message)

Rollback Service will rollback Txns
https://thorben-janssen.com/data-and-communication-patterns-for-microservices-waitlist/
https://www.youtube.com/watch?v=SUQxXg229Xg

https://www.youtube.com/watch?v=pSz0Fpvu2Gk

https://youtu.be/H6F4BorD49g - Hussein Nasser

What is a Distributed Transaction in Microservices?

What 3 Methods

1)Atomic Clocks - Rollback The steps
2)Event Based - Kafka/Rabbit MQ -> Publish/Subscribe -> Reverse
3)MiniMonolith - MacroService [Combine homogenous txns in 1 Service]
Distributed Transactions - Txns between Multiple Processes - Each with their own commit/rollback

Multiple Local Transactions - Dual Write - Inconsistencies

MiniMonolith - MacroService
Monorepo
Microservices

Youtube : Gears and Tools

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Audio Gear - Telusko

Lavalier - Mic

https://www.youtube.com/watch?v=gHn2dOF8TuU

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Karan Kaw's Blog

Wednesday, March 10, 2021

Syntax Highlighter , Preformatted Code

Cloud Design Patterns