Coupling (Eşleşme) Nedir - Architectural Principle

Giriş
Coupling iki bakış açısıyla tanımlanabilir.

1. Mimari Seviye
2. Tasarım Seviye

1. Mimari Seviyede Eşleşme
Mimari seviyeden bakarsak Coupling aslında bir Mimari Prensibi (Architectural Principle). Yani hangi Architectural Style veya hangi Architectural Pattern kullanılıyor olursa olsun bu kuralın dikkate alınması gerekiyor. Mimari seviyede Coupling dışındaki diğer bazı prensipler de şeklen şöyle.

Mimari seviyesindeki bakış açısıyla şöyle bir liste yapabiliriz.

There are degrees of loose coupling. It's not a binary state. This is not a complete list, but for the purposes of this discussion, some degrees are:

Level 0 - No abstractions, hardcoded references

Level 1 - Abstractions (interfaces), but everything in one project

Level 2 - One solution, separate projects abstractions

Level 3 - Abstractions are not part of the project but are loaded separately (think NuGet)

Level 4 - Independently hosted microservices

Level 3 ve 4 ile ilgili bazı açıklamalar şöyle. Level 3 standartlaşmaya doğru gitmiş ve muhtemelen tekrar kullanılabilen bir soyutlama seviyesinde. Ancak halen, Level 3 seviyesinde yapılan bir değişiklik diğer kod parçalarında tekrar derlemeye sebep oluyor.

Level 3 moves the abstraction out of the solution, so that it can live its own life. This is the most useful when more than one solution consumes this abstraction, or when the developers of the abstraction are a completely different team from the developers of the main product. Maybe it's a different company team, maybe they're different companies altogether.

You've probably used several third party libraries. How much did you know about their teams, who developed them, or the internals of the library they created? Not much. And that's the point, because the abstraction is so loosely coupled to the end product that you don't even need to know anything (other than its interface) about it anymore.

But level 3 still suffers a specific problem: if the abstraction gets updated, then all of its consumers will have to rebuild (or at the very least re-release) to account for these new changes. This requires an active line of communication, at least one-way (e.g. a third party developer's news feed announcing a patch to fix issues or expand the feature set).

This is what level 4 (microservices) solve. Because it's now an independently deployed application, any published change goes live for every consumer at the same time. The consumers don't need to change anything or re-release their own application.

As long as the interface or public URL doesn't change, the two services don't even need to communicate anything about any of their changes.

Örnek

Bir örnek şöyle

A very clear example of why this is desirable is e.g. an identity provider.

- Levels 0/1/2 all amount to authorization for this specific application.

- Level 3 makes it possible to standardize identity management across all of the library's consumers, but in the end each consumer is still choosing to update to new versions of the library individually.

- By having this as a microservice (level 4), any changes made to the identity provider (e.g. changed rights, user access, different security protocols) automatically deploy everywhere at the same time, and the developers of the consuming applications don't even need to be kept in the loop at any stage.

Microservice Mimarisinde Low Coupling
Level 4 ile coupling seviyesi en düşük olan seviye bu. Bu seviyede artık değişiklikler yüzünden kodu tekrar derleme azalıyor. Açıklaması şöyle.

services know little about each other. A change to one service should not require changing the others. Communication between services should happen only through public service interfaces.

Eğer low coupling olmazsa açıklaması şöyle.

Without loose coupling, changes to one service affect other services, so we would not be able to release changes fast and safely, which is the core benefit of microservice architecture. More importantly, issues caused by tight coupling could be disastrous, e.g., data inconsistencies or even data loss.

2. Tasarım Seviyesinde Eşleşme
Tasarım Seviyesinde Eşleşme - Coupling yazısına taşıdım