從整體到微服務：.NET應用程序的遷移指南

遷移.NET單體應用到微服務應避免一次性重寫，1. 首先明確遷移動機並規避常見陷阱，確保團隊具備DevOps與可觀測性能力；2. 採用絞殺者模式逐步替換，通過API網關路由新功能至新服務；3. 運用領域驅動設計識別限界上下文，按業務邊界拆分服務並隔離數據庫；4. 選擇合適的通信方式，對用戶請求用HTTP/REST，對事件用異步消息如Azure Service Bus；5. 通過事件最終一致性、Saga模式和Outbox模式保障跨服務數據一致性；6. 早期集成Serilog、OpenTelemetry等工具構建日誌、追踪與指標監控體系；7. 為每個服務建立獨立的CI/CD流水線，使用Docker容器化並部署至Kubernetes等平台。該過程是漸進式演進而非一次性項目，需以小步驗證、持續保障系統穩定運行結束。

Migrating a .NET monolith to microservices isn't about rewriting everything at once—it's about breaking down a complex system into manageable, independent services while maintaining business continuity. Done right, this shift improves scalability, team autonomy, and deployment velocity. But getting there requires strategy, patience, and a few key patterns.

Here's how to approach the migration in a practical, low-risk way.

1. Start with the Right Motivation (and Avoid Common Pitfalls)

Before writing a single line of code, ask: Why are we moving to microservices?

Common valid reasons:

• Teams are stepping on each other's code.
• Deployment cycles are too long.
• Certain parts of the app need to scale independently.
• You're introducing new tech stacks or deployment models.

Red flags:

• “Because everyone else is doing it.”
• No DevOps or CI/CD pipeline in place.
• Lack of monitoring or observability.

Microservices add operational complexity. If your team isn't ready to manage distributed systems, you'll tr​​ade one set of problems for a harder one.

2. Use the Strangler Pattern to Incrementally Replace the Monolith

The Strangler Pattern lets you gradually replace parts of your monolith without a risky “big bang” rewrite.

How it works:

• Keep the existing monolith running.
• Route new functionality (or high-impact modules) into new microservices.
• Use API gateways or reverse proxies to route requests: old paths go to the monolith, new ones go to microservices.
• Over time, more functionality is “strangled” out of the monolith.

Example in .NET: Suppose your monolith has a tightly coupled Order and Inventory module. You can:

• Extract Inventory into a standalone service using ASP.NET Core Web API.
• Deploy it as a separate app (eg, on Kubernetes or Azure App Service).
• Update the monolith to call the new Inventory API instead of using in-process logic.
• Eventually, deprecate the old inventory code.

Tools like Ocelot or YARP (Yet Another Reverse Proxy) can help route traffic during transition.

3. Identify Bounded Contexts Using Domain-Driven Design (DDD)

Not every class or folder should become a service. Use DDD to find natural boundaries.

Ask:

• Which parts of the system change together?
• What data is tightly coupled?
• Who owns this feature (team boundaries)?

For example, in an e-commerce app:

• Orders → Order Service
• Payments → Payment Service
• Users → Identity Service
• Product Catalog → Catalog Service

Each service should own its data. Avoid shared databases. In .NET, this means:

• Each service has its own DbContext.
• Use Entity Framework Core with isolated databases.
• Prefer asynchronous communication (eg, via messaging) over direct DB access.

4. Choose the Right Communication Style

In a monolith, method calls are in-process and fast. In microservices, you must handle network calls.

Options in .NET:

• HTTP/REST – Simple, widely supported. Use HttpClient or Refit.
• gRPC – Faster, contract-first, great for internal services. Built into .NET 5 .
• Messaging (eg, RabbitMQ, Azure Service Bus) – Enables async, decoupled communication.

Best practice:

• Use synchronous (HTTP) for request/response with user-facing APIs.
• Use async messaging for background tasks or inter-service events (eg, “OrderCreated” → trigger inventory deduction).

Example with Azure Service Bus in .NET:

 // Publishing an event
await sender.SendMessageAsync(new ServiceBusMessage(JsonSerializer.Serialize(order)));

Use libraries like MassTransit or NServiceBus to simplify messaging patterns.

5. Handle Data Consistency Across Services

One of the biggest challenges: you can't use distributed transactions easily.

Solutions:

• Eventual consistency – Accept that data may be temporarily out of sync.
• Saga pattern – Break long operations into steps with compensating actions.
• Outbox pattern – Store events in the same DB transaction, then publish them reliably.

In .NET, you can implement the outbox using:

• A table to store outgoing events.
• A background service ( IHostedService ) that polls and publishes.

This avoids dual writes and ensures reliability.

6. Build Observability Early

With distributed systems, debugging becomes harder.

Essential tools for .NET:

• Logging – Use Serilog with structured logging.
• Tracing – Enable OpenTelemetry in ASP.NET Core to track requests across services.
• Metrics – Expose Prometheus endpoints with OpenTelemetry.Exporter.Prometheus .
• Health checks – Use MapHealthChecks() in Program.cs.

Example:

 builder.Services.AddOpenTelemetryTracing(tracing => {
    tracing.AddAspNetCoreInstrumentation()
           .AddHttpClientInstrumentation()
           .AddOtlpExporter(); // Send to Jaeger or Grafana Tempo
});

Set this up from day one. You'll thank yourself later.

7. Automate Deployment and CI/CD

Each microservice should be independently deployable.

In .NET, this means:

• One Git repo per service (or use a monorepo with careful pipelines).

• Separate CI/CD pipelines (Azure DevOps, GitHub Actions).

• Containerize with Docker:

   FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
  WORKDIR /app
  EXPOSE 8080
  
  FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
  WORKDIR /src
  COPY . .
  RUN dotnet publish -c Release -o /app/out
  
  FROM base AS final
  WORKDIR /app
  COPY --from=build /app/out .
  ENTRYPOINT ["dotnet", "OrderService.dll"]

  Deploy to Kubernetes, Azure Container Apps, or similar.

  ---

  Final Thoughts

  Migrating from a .NET monolith to microservices is a journey, not a project. Start small: pick one well-bounded module, extract it safely using the Strangler Pattern, and validate the operational overhead.

  Focus on team autonomy, independent deployability, and resilience—not just technology.

  Use the .NET ecosystem wisely: leverage ASP.NET Core, Entity Framework, OpenTelemetry, and modern cloud platforms to reduce friction.

  It's not about replacing the monolith overnight. It's about making the system easier to evolve—one service at a time.

  Basically, take small steps, measure impact, and keep the lights on.

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