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microservice-patterns

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Microservice pattern demos (Saga, EventSourcing, CQRS...) running on .NET Aspire

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# MicroservicePatterns – Advanced microservice patterns on .NET Aspire

This repository is a set of **focused, production-inspired demos** showing how to implement complex microservice patterns on **.NET** using **.NET Aspire**.

The goal is simple:

> Strip away domain noise and framework boilerplate so you can clearly see  
> **what each pattern does, why you need it, and how to implement it.**

If you care about high-quality microservice architecture on .NET, this repo is for you.

---

## Why this repository?

Most examples of microservices either:

- oversimplify patterns to the point where they are unrealistic, or  
- drown you in domain complexity, infrastructure, and unrelated concerns.

This project takes a different approach:

- **Pattern-first**: Each demo is built around a single architectural problem.
- **Minimal domain**: Just enough domain to make the scenario realistic.
- **Aspire-native**: Uses .NET Aspire to bootstrap and orchestrate services.
- **Teachable**: Designed to be read, explored, and modified.

Use it as a learning lab, a reference implementation, or a starting point for your own experiments.

---

## Patterns covered

### CQRS (Command Query Responsibility Segregation)

**Problem:**  
How do you query data efficiently when it lives in **multiple distributed stores**, and reads start to outnumber writes?

**What this demo shows:**

- Splitting **write models** (commands) from **read models** (queries).
- Building **read models** that aggregate data from multiple services.
- Improving **read performance and scalability** without over-complicating the write side.

---

### Event Sourcing

**Problem:**  
How do you model **complex aggregates** and still keep updates atomic, auditable, and easy to reason about?

**What this demo shows:**

- Representing changes as **events** instead of overwriting state.
- Rebuilding current state by **replaying the event stream**.
- Keeping a **full history** of an entity’s lifecycle for debugging, audits, and analytics.
- Treating complex updates as sequences of **small atomic events**.

---

### Saga (Orchestration & Choreography)

**Problem:**  
How do you implement a **business transaction spanning multiple microservices** without using distributed transactions?

**What these demos show:**

- **Orchestration-based Sagas**  
  - A central **Saga orchestrator** coordinates each step.
  - Clear flow and central control.

- **Choreography-based Sagas**  
  - Services react to **domain events** and perform their own steps.
  - No central brain; the flow emerges from **event handling**.

You’ll see how to handle **success, failure, retries, and compensation** across services.

---

### Transactional Outbox

**Problem:**  
How do you ensure that when a service updates its database **and** publishes an integration event, **either both happen or neither do**?

**What this demo shows:**

- Writing changes and outgoing events into the **same database transaction**.
- Using an **outbox table** and a background process to publish events reliably.
- Avoiding the classic “DB updated, message not sent” inconsistency.

This pattern underpins reliable **event-driven communication** between services.

---

### Webhook

**Problem:**  
How do you build **event-driven integrations** where external systems subscribe to your events instead of you polling them?

**What this demo shows:**

- Registering and managing **webhook subscriptions**.
- Sending **notifications** to third-party endpoints when events occur.
- Basic patterns for **retries**, **verification**, and **security** around webhooks.

This is the backbone for “notify me when X happens” style integrations.

---

## Supporting building blocks

### CloudEvents

Standardizing event envelopes using the **CloudEvents** specification makes it much easier to:

- Integrate with other platforms and languages.
- Route and inspect events in a consistent way.
- Treat your system as a set of **composable event-driven services**.

The demos show how to emit and consume events using the CloudEvents format.

---

### Mediator

To reduce tight coupling between parts of your system, this repo includes a **Mediator** implementation with the same goals as libraries like MediatR, but with a **fresh implementation** (after MediatR’s license change).

You’ll see how to:

- Send **commands** and **queries** without components depending directly on each other.
- Centralize cross-cutting behaviors (logging, validation, etc.) via **pipeline behaviors**.

---

### Circuit Breaker

Distributed systems fail in **messy** ways.

The Circuit Breaker demos show how to:

- Fail fast when a downstream service is **unhealthy**.
- Prevent cascading failures from taking down your system.
- Gradually **recover** when the remote service stabilizes.

This is one of the most important patterns for **resilient microservices**.

---

## Repository layout

At a high level:

- `MicroservicePatterns.AppHost`  
  The **.NET Aspire AppHost** project that wires everything together and orchestrates the services.

- `patterns/`  
  The individual pattern demos (CQRS, Event Sourcing, Saga, etc.).  
  Each pattern is organized to keep the focus on **the pattern itself**, not on an over-engineered domain.

- `EventBus`, `EventBus.Kafka`  
  Infrastructure for publishing/consuming integration events.  
  Includes a Kafka-based implementation to show how patterns play with a real event bus.

- `Mediator`  
  The custom Mediator implementation used by the demos.

- `MicroservicePatterns.Shared`, `MicroservicePatterns.ServiceDefaults`, `MicroservicePatterns.DatabaseMigrationHelpers`  
  Shared abstractions, defaults, and helpers to keep the pattern demos **clean and readable**.

You can browse the `patterns/` folder and open the pattern you’re interested in; each is built to be read in isolation.

---

## Getting started

### Prerequisites

- **.NET SDK** (latest version that supports .NET Aspire)  
- **.NET Aspire** workloads and toolings installed  
  (follow the official .NET Aspire documentation for your platform).
  
### Run the solution

1. Clone the repo:

```bash
   git clone https://github.com/daohainam/microservice-patterns.git
   cd microservice-patterns
   ```

2. Restore and build:

```bash
   dotnet restore
   dotnet build
   ```

4. Start the Aspire app host:

```bash
   dotnet run --project MicroservicePatterns.AppHost
   ```

6. Open the Aspire dashboard (if enabled) and explore the running services and patterns.

From there, pick a pattern, follow the comments in the code, and run through typical scenarios (success paths, failures, compensations, etc.).

---

## Learn with the videos

This repository is designed to be used together with detailed video explanations:

Pattern deep dives (CQRS, Event Sourcing, Saga, Outbox, Webhook, etc.)
Playlist:
https://www.youtube.com/playlist?list=PLRLJQuuRRcFlOIjMY9w5aoCf6e368oxez

Getting started with .NET Aspire via a Core Banking (fake) exercise
A practical intro to building on Aspire, which helps when navigating this repo:
https://youtu.be/QVPYhhp-Nkg

Watch a video, then jump into the corresponding pattern in this repo and step through the code.

---

## Who is this for?

.NET developers who want to go beyond basic Web APIs and understand real microservice patterns.

Architects and tech leads evaluating .NET Aspire for microservice platforms.

Learners and teachers looking for clean, focused examples to explain advanced patterns.

If you use this repo in a talk, workshop, or course, feel free to link back and share how you’re using it.

---

## Status & contributions

This project is deliberately opinionated and minimal, not a full production system.
It’s meant as a reference and teaching tool.

If you find bugs, have questions, or want to propose improvements to the demos, contributions and discussions are very welcome via issues and pull requests.

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