Creating a Stateful Service in Azure Service Fabric

Creating a Stateful Service in Service Fabric

After learning about Stateless services, it’s time to understand and create a Stateful Service in Service Fabric. Stateful services are powerful because they maintain data consistency across replicas without needing an external database!

🌟 What is a Stateful Service?

A Stateful Service maintains internal state across client requests. Service Fabric itself ensures the data is replicated, consistent, and available even during node failures.

• Examples: Shopping cart data, Game session state, IoT device telemetry processors.
• Provides automatic high availability via replicas.

Real-World Analogy:

Think of a library system — every time you borrow or return a book, your data (borrow history) is stored carefully and replicated to avoid loss.

🛠️ Prerequisites

• Service Fabric SDK installed.
• Cluster running (local or Azure).
• Visual Studio installed.

🚀 Step-by-Step Guide: Create and Deploy a Stateful Service

Step 1: Create a New Service Fabric Application

1. Open Visual Studio.
2. File → New → Project → Search Service Fabric Application.
3. Name it StatefulAppDemo (or your choice).
4. Click Create.

Step 2: Add a Stateful Service

1. In the service selection window, choose: Stateful Service (C# Worker).
2. Click OK.

Step 3: Understand the Generated Code

• The service class inherits from:

  public class YourServiceName : StatefulService
              

• Important Overridden Methods:
  • CreateServiceReplicaListeners: Setup listeners for client communication.
  • RunAsync: Main execution loop for background tasks.
• StateManager: Built-in object for handling reliable dictionaries and queues (auto-replicated).

Step 4: Working with StateManager

Example of using a reliable dictionary to store key-value pairs:

var myDictionary = await StateManager.GetOrAddAsync>("myDictionary");

using (var tx = StateManager.CreateTransaction())
{
    await myDictionary.AddOrUpdateAsync(tx, "counter", 0, (key, value) => value + 1);
    await tx.CommitAsync();
}
    

Step 5: Build and Deploy the Application

• Build the solution.
• Publish to Local or Azure Cluster (Right-click → Publish).

Step 6: Monitor the Service

• Open Service Fabric Explorer.
• Check your Application → Service → Partitions → Replicas.
• Healthy replicas indicate successful deployment and state replication.

📈 Visual Flow Summary

[Create New SF App] 
    → [Add Stateful Service] 
        → [Work with StateManager]
            → [Build and Publish]
                → [Monitor Replicas]
    

💡 Did You Know?

⚡ Common Beginner Issues and Solutions

• Problem: Replica drop or 'Not Ready' status.
  Solution: Check if VM resources are sufficient. Add more nodes if needed.
• Problem: State not persisted.
  Solution: Ensure you call CommitAsync() after modifying state inside transactions.
• Problem: Slow service start.
  Solution: Avoid expensive blocking operations inside RunAsync().

🚨 Best Practices

• Use batching when writing a lot of data to StateManager (commit multiple operations together).
• Design idempotent operations to survive service restarts and retries.
• Keep service instances lightweight — move heavy processing to external queues if needed.

✅ Self-Check Quiz

• What is the purpose of the StateManager?
• Why do we need CommitAsync() inside transactions?
• What happens if a primary replica fails?