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Modular Monolith

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

2 Trainings from ardalis:

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

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