C# Architecture Mastery — Event-Driven Architecture in .NET (Clean Boundaries with Messaging) (Part 12)
Event-Driven Architecture (EDA) is often introduced too late or too aggressively.
Some teams avoid it because it feels complex.
Others jump straight into brokers, sagas, and eventual consistency without boundaries.
Both approaches miss the point.
In this Part 12, we’ll explain how to use events to reinforce Clean Architecture boundaries in .NET, when messaging is the right tool, and how senior teams avoid turning EDA into distributed chaos.
1. What Event-Driven Architecture Really Is
At its core, EDA means:
State changes are communicated via events, not direct calls.
An event:
- Describes something that already happened
- Is immutable
- Has no expectations about who listens
Events are facts, not commands.
2. Why Events Strengthen Clean Architecture
Clean Architecture is about decoupling.
Events:
- Reduce temporal coupling
- Remove direct dependencies
- Enable independent evolution
- Improve team autonomy
Used correctly, events protect boundaries instead of weakening them.
3. Commands vs Events (Critical Distinction)
| Concept | Meaning |
|---|---|
| Command | Intent to do something |
| Event | Notification that something happened |
// Command
CreateOrder
// Event
OrderCreated
Commands expect a result.
Events do not.
Confusing these leads to fragile systems.
4. Where Events Live in Clean Architecture
In Clean Architecture:
- Domain events belong to the Domain
- Integration events belong to the Application / Infrastructure boundary
- Messaging infrastructure belongs to Infrastructure
Boundaries matter.
5. Domain Events (Inside the Core)
Domain events capture meaningful business moments.
public record OrderCreated(OrderId Id, decimal Total);
They are raised by entities or aggregates:
AddDomainEvent(new OrderCreated(Id, Total));
Domain events:
- Are synchronous inside the boundary
- Do not depend on brokers
- Do not cross process boundaries directly
6. Integration Events (Cross-Boundary Communication)
Integration events are published after transactions succeed.
They are:
- Serializable
- Stable contracts
- Versioned
public record OrderCreatedIntegrationEvent(Guid OrderId, decimal Total);
These events cross:
- Services
- Modules
- Teams
7. Messaging Infrastructure in .NET
Common tools:
- Azure Service Bus
- RabbitMQ
- Kafka
- Amazon SQS/SNS
The rule:
The domain must never know which one you use.
Infrastructure adapts events to brokers.
8. Eventual Consistency (The Honest Trade-Off)
EDA trades:
- Strong consistency for
- Scalability and autonomy
Senior teams accept:
- Temporary inconsistency
- Retry logic
- Idempotency
- Observability requirements
If you can’t tolerate this, EDA is the wrong choice.
9. Common Event-Driven Smells
🚨 Warning signs:
- Business logic in message handlers
- Commands disguised as events
- Chatty event storms
- Tight coupling via message schemas
- Missing idempotency
These are boundary violations — not tooling issues.
10. When Event-Driven Architecture HELPS
EDA is valuable when:
- Multiple teams need the same signals
- Side effects should not block core flows
- Systems evolve independently
- Scaling and resilience matter
Typical use cases:
- Notifications
- Auditing
- Projections / read models
- Cross-service workflows
11. When Event-Driven Architecture HURTS
EDA hurts when:
- The domain is simple
- Strong consistency is required
- Teams lack observability maturity
- Messaging is added "just in case"
Events add power — and responsibility.
12. Senior-Level Messaging Checklist
Before adopting EDA, ask:
- What boundary does this event protect?
- Is this a fact or a request?
- Who owns the event contract?
- Can consumers fail independently?
- Is idempotency handled?
If you can’t answer these, stop.
Final Thoughts
Event-Driven Architecture is not about brokers.
It’s about decoupling decisions.
Used correctly:
- It reinforces Clean Architecture
- It enables team autonomy
- It scales naturally
Used poorly:
- It hides coupling
- It spreads complexity
- It destroys trust
Messaging should serve architecture — never replace it.
✍️ Written by Cristian Sifuentes — helping teams design event-driven .NET systems with clear boundaries, resilient messaging, and architectural discipline.
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