Modular Monolith

https://www.milanjovanovic.tech/blog/modular-monolith-communication-patterns

2 Trainings from ardalis:

• Part 1: Getting Stared: https://dometrain.com/bundle/from-zero-to-hero-modular-monoliths-in-dotnet/
• Part 2: Deep Dive: https://courses.dometrain.com/courses/take/deep-dive-modular-monoliths-in-net/

Part 1: Getting Started

My thougts about Getting Started

• watch ardalis to type for hours
• example uses EF + SQL Server
• repo pattern, but no generic repo
• no regular or minimal API, instead he uses https://fast-endpoints.com/
  • needs special packages for security, swagger
• uses MediatR
  • configured to load from different assemblies
• uses Microsoft Identity (I'd prefer OAuth/OIDC approach)
• if you know how to create an ASP.NET app (EF, Repository, MediatR), don't buy this course: go directly to the 'Deep dive'

Module Communication options

1. ask for it over HTTP --> slow, high coupling
2. just query the book table directly --> high coupling
3. call /books/{id} over http --> slow, high coupling
4. call BookService directly --> high coupling
5. make a loosely-coupled call via MediatR --> ok
6. use materialized view --> ok (part 2 of this training)

Learnings

• if you have 1 database: separate data using db-schema
• modules (books, users) communicate by MediatR
  • book module (3 assemblies: book, book.Tests, Book.Contracts)
  • user module (contains cart)
• needs an additional module (assembly Book.Contracts - between Modules Users and Books)
  • no direct dependency between book and user (loosly coupled)
  • move MediatR request/response class to this contracts module
  • move MediatR queries and handlers to an \Integration folder (or "\ExternalInterface" or "\PublicInterface")
  • avoid global contracts module - have one for each module

Part 2: Deep dive

My thoughts about Deep Dive

Module communication patterns

• Direct Calls : ok
  • Project reference - compile time
  • Reflection - run time
• Mediated Call (MediatR) : ok
• Shared State (DB, File, ...) : Non Blocking
• Message Bus Messages (Command, Event) : Non Blocking
• Message Bus Messages (Queries: 2 queues) : Blocking
• Store and Forward (Outbox) : Non Blocking
• Cache and Subscribe (Materialized View pattern) : Non Blocking
• General Classes: move to .SharedKernel

Links

• Check Architecture using ArchUnit https://archunitnet.readthedocs.io/en/latest/guide/