The Saga Pattern in Microservices

Hi devs,

Microservices have revolutionized how we build scalable and flexible systems. However, they also introduce complexities, especially when managing distributed transactions across services. That's where the Saga Pattern comes in—a powerful design pattern for handling long-running transactions in microservices. In this post, we’ll explore what the Saga Pattern is, how it works, and see it in action with a Human Resources (HR) use case in C#.

What is the Saga Pattern?

The Saga Pattern breaks a large, distributed transaction into a series of smaller steps, each handled by a specific microservice. These steps are executed in sequence, with compensating actions defined for each step to rollback if something goes wrong.

There are two primary approaches to implementing the Saga Pattern:

1. Choreography: Each service listens for and reacts to events, orchestrating itself.
2. Orchestration: A central coordinator service manages the flow of the transaction.

Why Use the Saga Pattern?

The Saga Pattern is particularly useful for microservices architectures where:

• Transactions span multiple services (e.g., HR, payroll, recruitment).
• Scalability and decoupling are essential.
• It’s crucial to handle partial failures gracefully.

HR Use Case: Employee Onboarding

Imagine a Human Resources (HR) system where onboarding a new employee involves multiple microservices:

1. User Service: Creates an employee account.
2. Payroll Service: Sets up payroll details.
3. Benefits Service: Registers the employee for benefits.

These services must work together to complete the onboarding process. If the Payroll Service fails, the system should undo the account creation and benefits registration.

Implementing the Saga Pattern in C

Let’s implement the Saga Pattern with orchestration for the employee onboarding process.

Step 1: Define the Saga Coordinator

The Saga Coordinator manages the flow of the transaction. Here’s a basic implementation in C#:

public class SagaCoordinator
{
    private readonly IUserService _userService;
    private readonly IPayrollService _payrollService;
    private readonly IBenefitsService _benefitsService;

    public SagaCoordinator(IUserService userService, IPayrollService payrollService, IBenefitsService benefitsService)
    {
        _userService = userService;
        _payrollService = payrollService;
        _benefitsService = benefitsService;
    }

    public async Task ExecuteOnboardingSagaAsync(Employee employee)
    {
        try
        {
            Console.WriteLine("Starting onboarding saga...");

            // Step 1: Create user account
            await _userService.CreateUserAsync(employee);

            // Step 2: Set up payroll
            await _payrollService.SetupPayrollAsync(employee);

            // Step 3: Register benefits
            await _benefitsService.RegisterBenefitsAsync(employee);

            Console.WriteLine("Onboarding completed successfully!");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error during onboarding: {ex.Message}");
            await CompensateAsync(employee);
        }
    }

    private async Task CompensateAsync(Employee employee)
    {
        Console.WriteLine("Compensating...");
        await _benefitsService.RollbackBenefitsAsync(employee);
        await _payrollService.RollbackPayrollAsync(employee);
        await _userService.DeleteUserAsync(employee);
        Console.WriteLine("Compensation complete.");
    }
}

Step 2: Define the Services

Each service implements its specific logic and compensating actions.

public interface IUserService
{
    Task CreateUserAsync(Employee employee);
    Task DeleteUserAsync(Employee employee);
}

public interface IPayrollService
{
    Task SetupPayrollAsync(Employee employee);
    Task RollbackPayrollAsync(Employee employee);
}

public interface IBenefitsService
{
    Task RegisterBenefitsAsync(Employee employee);
    Task RollbackBenefitsAsync(Employee employee);
}

Implementations of these interfaces would interact with databases or other APIs.

Step 3: Execute the Saga

Here’s how you can use the Saga Coordinator:

public class SagaCoordinator
{
    private readonly IUserService _userService;
    private readonly IPayrollService _payrollService;
    private readonly IBenefitsService _benefitsService;

    public SagaCoordinator(IUserService userService, IPayrollService payrollService, IBenefitsService benefitsService)
    {
        _userService = userService;
        _payrollService = payrollService;
        _benefitsService = benefitsService;
    }

    public async Task ExecuteOnboardingSagaAsync(Employee employee)
    {
        try
        {
            Console.WriteLine("Starting onboarding saga...");

            // Step 1: Create user account
            await _userService.CreateUserAsync(employee);

            // Step 2: Set up payroll
            await _payrollService.SetupPayrollAsync(employee);

            // Step 3: Register benefits
            await _benefitsService.RegisterBenefitsAsync(employee);

            Console.WriteLine("Onboarding completed successfully!");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error during onboarding: {ex.Message}");
            await CompensateAsync(employee);
        }
    }

    private async Task CompensateAsync(Employee employee)
    {
        Console.WriteLine("Compensating...");
        await _benefitsService.RollbackBenefitsAsync(employee);
        await _payrollService.RollbackPayrollAsync(employee);
        await _userService.DeleteUserAsync(employee);
        Console.WriteLine("Compensation complete.");
    }
}

Advantages of the Saga Pattern

1. Resilience: Enables recovery from failures in long-running processes.
2. Scalability: Decouples services while maintaining transactional integrity.
3. Flexibility: Supports diverse workflows by tailoring compensation logic.

Final Thoughts

The Saga Pattern is a critical design pattern for maintaining data consistency in distributed systems like microservices. In our HR example, it ensured the entire onboarding process either completed successfully or rolled back gracefully, preserving system integrity.

By leveraging patterns like Saga, we can design robust systems that handle the complexities of distributed transactions.

Keep coding

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