In the ever-changing world of software development, the microservices architecture has become a popular choice, especially in the vast realm of .NET. With its ability to scale and adapt, .NET is an ideal platform for building microservices-based applications. This allows developers to create robust, distributed systems that can handle large volumes of data and traffic.

In this article, we’ll explore five essential patterns for .NET developers who want to master microservices architecture. We’ll provide practical examples and actionable advice to help you on your journey towards achieving microservices excellence.

1. The Gateway Aggregation Pattern

In a microservices architecture, it’s common to have multiple services that a client application needs to interact with. Rather than having the client directly interact with each individual service, it’s better to use an API gateway. This approach simplifies the client code and creates a single entry point for accessing the backend services.

//Example using Ocelot API Gateway
public async Task<AggregatedResult> AggregateData()
{
var userTask = _userService.GetUser();
var ordersTask = _orderService.GetOrdersForUser();

await Task.WhenAll(userTask, ordersTask);

var user = await userTask;
var orders = await ordersTask;

return new AggregatedResult
{
User = user,
Orders = orders
};
}

2. The Circuit Breaker Pattern

Implementing a circuit breaker can help prevent a network or service outage from spreading to other services. When a service outage occurs, the circuit breaker detects it and automatically blocks subsequent calls to that service for a predetermined period of time.

//Example using Polly library
var circuitBreakerPolicy = Policy
.Handle<Exception>()
.CircuitBreaker(2, TimeSpan.FromMinutes(1));

await circuitBreakerPolicy.ExecuteAsync(async () =>
{
await PerformServiceCall();
});

3. The Service Discovery Pattern

As you scale out your microservices architecture, it becomes more challenging to keep track of all the different service endpoints. To solve this problem, you can implement service discovery, which allows services to find each other dynamically.

using System;
using System.Threading.Tasks;
using Consul;
using Microsoft.Extensions.DependencyInjection;

class Program
{
static void Main(string[] args)
{
var serviceProvider = new ServiceCollection()
.AddSingleton<IConsulClient, ConsulClient>(p => new ConsulClient(consulConfig =>
{
// Assuming Consul is running on localhost
consulConfig.Address = new Uri("http://localhost:8500");
}))
.AddSingleton<IConsulService, ConsulService>()
.BuildServiceProvider();

var consulService = serviceProvider.GetService<IConsulService>();
consulService.RegisterService().Wait();
consulService.DiscoverServices().Wait();
}
}

public interface IConsulService
{
Task RegisterService();
Task DiscoverServices();
}

public class ConsulService : IConsulService
{
private readonly IConsulClient _consulClient;

public ConsulService(IConsulClient consulClient)
{
_consulClient = consulClient;
}

public async Task RegisterService()
{
var registration = new AgentServiceRegistration()
{
ID = Guid.NewGuid().ToString(),
Name = "MyService",
Address = "localhost",
Port = 5000,
};

await _consulClient.Agent.ServiceRegister(registration);
Console.WriteLine("Service registered with Consul");
}

public async Task DiscoverServices()
{
var services = await _consulClient.Agent.Services();
foreach (var service in services.Response.Values)
{
Console.WriteLine($"Discovered service: {service.Service}");
}
}
}

4. The Event-Sourcing Pattern

Event sourcing is a pattern that involves storing the state changes of your application’s entities as a series of events. This approach is particularly useful in a microservices architecture, as it provides an auditable record of all changes made to the system, which can be helpful for debugging and troubleshooting. Additionally, event sourcing can help ensure data consistency across different components of the application.

//Example event sourcing with EventStore
public async Task SaveEvents(Guid entityId, IEnumerable<Event> events, long expectedVersion)
{
var eventData = events.Select(e => new EventData(
Guid.NewGuid(),
e.GetType().Name,
true,
Serialize(e),
null));

var streamName = $"Entity-{entityId}";
await _eventStoreConnection.AppendToStreamAsync(streamName, expectedVersion, eventData);
}

5. The CQRS Pattern

Command Query Responsibility Segregation (CQRS) is a design pattern that separates the read and write operations of a system. This approach is well-suited for microservices, as it helps to manage complex data models and scale systems more effectively.

Command to Add a New User

// Commands/AddUserCommand.cs
public class AddUserCommand
{
public string Name { get; }

public AddUserCommand(string name)
{
Name = name;
}
}

// Handlers/AddUserCommandHandler.cs
public class AddUserCommandHandler : ICommandHandler<AddUserCommand>
{
public void Handle(AddUserCommand command)
{
// Logic to add the user to the database
Console.WriteLine($"User {command.Name} added");
}
}

Query to Get a User by ID

// Queries/GetUserQuery.cs
public class GetUserQuery
{
public int UserId { get; }

public GetUserQuery(int userId)
{
UserId = userId;
}
}

// Handlers/GetUserQueryHandler.cs
public class GetUserQueryHandler : IQueryHandler<GetUserQuery, User>
{
public User Handle(GetUserQuery query)
{
// Logic to retrieve the user from the database
return new User { Id = query.UserId, Name = "John Doe" };
}
}

Interfaces for Handlers

// Commands/ICommandHandler.cs
public interface ICommandHandler<TCommand>
{
void Handle(TCommand command);
}

// Queries/IQueryHandler.cs
public interface IQueryHandler<TQuery, TResult>
{
TResult Handle(TQuery query);
}

By following these five patterns, you’ll be well on your way to mastering .NET microservices. Use them as building blocks and customize them to fit your projects. Your microservices will flourish. Have fun coding!