Section 4 of 6

Microservices Patterns

🎯 What You'll Learn

What are microservices
API Gateway pattern
Service discovery
Circuit breaker
Retry policies

What are Microservices?

Microservices are small, independent services that communicate over HTTP/gRPC, each responsible for a specific business capability.

Monolith vs Microservices

Aspect	Monolith	Microservices
Deployment	Single unit	Independent services
Scaling	Scale entire app	Scale individual services
Technology	Single stack	Different stacks per service
Complexity	Lower	Higher
Failure	Entire app fails	Isolated failures

API Gateway Pattern

Single entry point for all client requests, routing to appropriate microservices.

Install Ocelot Bash

dotnet add package Ocelot

ocelot.json JSON

{
  "Routes": [
    {
      "DownstreamPathTemplate": "/api/products/{everything}",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 5001
        }
      ],
      "UpstreamPathTemplate": "/products/{everything}",
      "UpstreamHttpMethod": [ "Get", "Post" ]
    },
    {
      "DownstreamPathTemplate": "/api/orders/{everything}",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 5002
        }
      ],
      "UpstreamPathTemplate": "/orders/{everything}",
      "UpstreamHttpMethod": [ "Get", "Post" ]
    }
  ]
}

Program.cs C#

builder.Configuration.AddJsonFile("ocelot.json");
builder.Services.AddOcelot();

var app = builder.Build();
await app.UseOcelot();

Circuit Breaker Pattern

Prevent cascading failures by stopping calls to failing services.

Install Polly Bash

dotnet add package Microsoft.Extensions.Http.Polly

Program.cs C#

using Polly;

builder.Services.AddHttpClient("ProductService", client =>
{
    client.BaseAddress = new Uri("http://localhost:5001");
})
.AddTransientHttpErrorPolicy(policy => 
    policy.CircuitBreakerAsync(5, TimeSpan.FromSeconds(30)));

Retry Policy

Retry with Polly C#

builder.Services.AddHttpClient("ProductService", client =>
{
    client.BaseAddress = new Uri("http://localhost:5001");
})
.AddTransientHttpErrorPolicy(policy => 
    policy.WaitAndRetryAsync(3, retryAttempt => 
        TimeSpan.FromSeconds(Math.Pow(2, retryAttempt))));

InvenTrack Microservices Example

OrderService calling ProductService C#

public class OrderService
{
    private readonly IHttpClientFactory _httpClientFactory;

    public async Task<Product> GetProductAsync(int productId)
    {
        var client = _httpClientFactory.CreateClient("ProductService");
        var response = await client.GetAsync($"/api/products/{productId}");
        response.EnsureSuccessStatusCode();
        
        return await response.Content.ReadFromJsonAsync<Product>();
    }
}

Key Takeaways

Microservices: Independent, scalable services
API Gateway: Single entry point (Ocelot)
Circuit breaker: Prevent cascading failures
Retry policy: Handle transient errors
Polly: Resilience library
Trade-offs: Higher complexity for better scalability