Retry Pattern - Microservice - How this helps on migration strategy

 

Retry Pattern

Several migration strategies were identified during the research, and this pattern stands out as an excellent approach. 

Its Role in Migration

The Retry Pattern handles transient faults, such as network failures or timeouts, during communication between services or components. During migration, where parts of a monolith are replaced with microservices, this pattern ensures resilience by automatically retrying failed operations.

 When to Use the Retry Pattern

Migrating modules with high-availability requirements like payments, order processing, or inventory updates. Scenarios involving third-party APIs or network-dependent components.

 Key Aspects of the Retry Implementation:

1. Retry Count: Limits retries to several attempts (configurable).
2. Exponential Backoff: Increases the wait time between retries to avoid overwhelming the service.
3. Fallback Mechanism: Returns an appropriate message if retries fail.

 Why Retry Pattern is Useful in Migration

Handles Temporary Failures:

During migration, new microservices or APIs may not always be stable. Retrying helps handle intermittent failures gracefully.

Improves User Experience:

Users won't see errors immediately if retries resolve temporary issues.

Supports Partial Migration:

Network or integration issues can be mitigated with retries when the monolith and microservices coexist.

 

Advantages of Using the Retry Pattern During Migration

Reduces risk of downtime when integrating with unstable or new microservices.

Ensures smooth user experience during the transitional phase.

Simplifies error handling by abstracting retracting into a reusable policy.

 

 

 

 

Use Case Example: Migrating Payment Processing

Imagine you’re migrating a Payment Processing module from a monolithic application to a microservice. The monolith still handles order creation, but the payment functionality has been moved to a microservice.

 

Monolith Code Before Migration

public class PaymentService

{

    public bool ProcessPayment(string orderId, decimal amount)

    {

        // Simulate payment processing logic

        return true;

    }

}

 

Post-Migration: Monolith Calls the Payment Microservice

The monolith makes HTTP calls to the payment microservice in the new setup. To handle transient failures, implement the Retry Pattern.

 

C# Example with Retry Pattern

Using Polly, a .NET library for resilience and transient fault handling:

4. Install Polly NuGet Package:

dotnet add package Polly

5. Implement the Retry Logic:

using System;

using System.Net.Http;

using System.Threading.Tasks;

using Polly;

using Polly.Retry;

 

public class PaymentService

{

    private readonly HttpClient _httpClient;

    private readonly AsyncRetryPolicy<HttpResponseMessage> _retryPolicy;

 

    public PaymentService(HttpClient httpClient)

    {

        _httpClient = httpClient;

 

        // Define the retry policy

        _retryPolicy = Policy

            .HandleResult<HttpResponseMessage>(r => !r.IsSuccessStatusCode)

            .Or<HttpRequestException>()

            .WaitAndRetryAsync(

                retryCount: 3,

                sleepDurationProvider: attempt => TimeSpan.FromSeconds(Math.Pow(2, attempt)),

                onRetry: (response, timespan, retryCount, context) =>

                {

                    Console.WriteLine($"Retrying... Attempt: {retryCount}");

                });

    }

 

    public async Task<bool> ProcessPayment(string orderId, decimal amount)

    {

        var paymentRequest = new

        {

            OrderId = orderId,

            Amount = amount

        };

 

        var httpRequest = new HttpRequestMessage(HttpMethod.Post, "http://payment-service/api/payments")

        {

            Content = new StringContent(System.Text.Json.JsonSerializer.Serialize(paymentRequest),

                System.Text.Encoding.UTF8, "application/json")

        };

 

        // Execute with retry

        var response = await _retryPolicy.ExecuteAsync(() => _httpClient.SendAsync(httpRequest));

 

        if (response.IsSuccessStatusCode)

        {

            Console.WriteLine("Payment processed successfully.");

            return true;

        }

 

        Console.WriteLine("Payment failed after retries.");

        return false;

    }

}

 

 

Steps in Migration with Retry Pattern

1. Migrate Payment Logic to a Microservice:

The payment service is deployed as a standalone microservice.

2. Integrate Retry Logic in the Monolith:

Add retry logic to handle network issues or temporary unavailability of the payment microservice.

3. Test in a Hybrid Environment:

Test the monolith and microservice integration with scenarios like timeouts and service restarts.