BookingMonolith

Booking Modular Monolith — Critter Stack Conversion

Original Project

Repository: meysamhadeli/booking-modular-monolith License: MIT Stack: .NET 10, MassTransit, MediatR, FluentValidation, EventStoreDB (event sourcing), EF Core (PostgreSQL), MongoDB (read models), gRPC (inter-module), Duende IdentityServer, .NET Aspire, Testcontainers

The richest original stack of all conversions. A travel booking system with 4 modules, event sourcing in the Booking module via EventStoreDB, MongoDB for read model projections, and gRPC for synchronous inter-module communication.

What Changed

Removed (7 infrastructure dependencies)

• EventStoreDB — replaced by Marten event store (same PostgreSQL)
• MongoDB — read model projections replaced by Marten inline snapshots
• MassTransit — replaced by Wolverine messaging + durable local queues
• MediatR — replaced by Wolverine handlers
• gRPC inter-module calls — replaced by direct Marten queries (same process)
• Duende IdentityServer — simplified to basic user registration
• Custom outbox/inbox — PersistMessageProcessor + ConsumeFilter replaced by Wolverine outbox

Before vs After

Aspect	Original	Converted
Projects	~15 (modules × layers + BuildingBlocks + Aspire)	1
Databases	PostgreSQL + EventStoreDB + MongoDB	PostgreSQL only (Marten)
Event store	EventStoreDB (gRPC client)	Marten event store
Read models	MongoDB projections + EventStore subscriptions	Marten inline snapshots
Message bus	MassTransit (RabbitMQ/InMemory)	Wolverine durable local queues
CQRS	MediatR + pipeline behaviors	Wolverine handlers
Inter-module sync	gRPC proto + generated clients	Direct Marten queries
Identity	Duende IdentityServer	Simple user registration

Event Sourcing (Booking module)

The original used EventStoreDB with a custom AggregateEventSourcing<T> base class, stream naming conventions, MongoDB projections, and EventStore subscription checkpoints.

Marten replaces all of this with:

// Event stream creation
session.Events.StartStream<BookingRecord>(bookingId, new BookingCreatedDomainEvent(...));

// Inline snapshot projection — no separate MongoDB read model needed
opts.Projections.Snapshot<BookingRecord>(SnapshotLifecycle.Inline);

Inter-Module Communication

The original used gRPC for synchronous calls (Booking → Flight, Booking → Passenger). In a monolith, these are unnecessary — the Booking handler queries Marten directly since all modules share the same process.

Running

Requires PostgreSQL only (no EventStoreDB, MongoDB, or RabbitMQ).

dotnet run

Swagger UI at /swagger.