What are Azure Functions

Azure Functions are a serverless compute service that lets you run small pieces of code (“functions”) in the cloud, without worrying about infrastructure. The main idea is that you write functions to respond to events (like HTTP requests, queue messages, blob uploads, timers, etc.). It is stateless, so each function execution is independent; by default, Azure Functions do not remember anything from one run to the next.

The following Use cases you can think of are

  • APIs and microservices
  • Responding to storage or queue events
  • Running scheduled jobs
  • Lightweight event-driven tasks

What are Azure Durable Functions

Azure Durable Functions extend Azure Functions by enabling the creation of stateful workflows in a serverless compute environment. With support for languages like C#, JavaScript, Python, and PowerShell, developers can orchestrate complex processes using simple code constructs. the amain idea is that it lets you orchestrate and coordinate multiple function calls, track state, and handle long-running workflows—all in a serverless way. It is statefull, so it remembers progress, checkpoints, and data between steps. Can wait for human interaction or external events and continue later.

The following Use cases you can think of are

  • Long-running processes (approval workflows, batch jobs)
  • Chained and fan-out/fan-in workflows
  • Human-in-the-loop tasks (wait for user approval)
  • Coordinating complex event-driven systems

to dive deep in terms of durable functions we will explain the core concepts

Core Concepts (Simplified)

Durable Functions consist of four core components:

  • Client Function: Starts the workflow, typically triggered by an HTTP request or message.
  • Orchestrator Function: Controls the flow of the process and calls activity functions in order.
  • Activity Function: Performs tasks like API calls, data processing, or database access.
  • Durable Task Framework: Manages state, timing, and retries automatically.

Architecture Overview

+--------------------+
|  Client Function   |
| (Trigger: HTTP, etc)|
+--------------------+
          |
          v
+--------------------+
| Orchestrator Func  |
|  (Workflow logic)  |
+--------------------+
      /      |      \
     v       v       v
+--------+ +--------+ +--------+
|Activity| |Activity| |Activity|
|Function| |Function| |Function|
+--------+ +--------+ +--------+

(Durable Task Framework manages state and checkpoints behind the scenes)

Common Application Patterns

Durable Functions support several powerful patterns for building workflows:

  • Function Chaining: Execute a sequence of functions where each step depends on the previous one.
  • Fan-Out/Fan-In: Run multiple functions in parallel and aggregate their results once all complete.
  • Async HTTP APIs: Handle long-running operations initiated by HTTP without blocking the caller.
  • Monitoring: Implement recurring checks or polling logic to monitor system status.
  • Human Interaction: Pause workflows until external inputs, such as approvals, are received.

Advantages

Durable Functions offer a number of significant benefits:

  • Simplified state management: Automatically maintains state and checkpoints between executions.
  • Built-in reliability: Supports automatic retries and error handling.
  • Serverless scalability: Automatically scales based on demand with consumption-based billing.
  • Code-centric design: Workflows are written in code, not JSON or other configuration formats.

Ideal Use Cases

Durable Functions are particularly useful for scenarios such as:

  • Order fulfillment and e-commerce workflows
  • Business approval processes
  • Periodic system health checks
  • Complex ETL and data processing tasks

Considerations and Limitations

While powerful, Durable Functions come with some trade-offs:

  • Potential cold start latency on consumption plans
  • Increased complexity in debugging large orchestrations
  • Limited features in some language runtimes compared to others

Conclusion

Azure Durable Functions provide a robust framework for building scalable, reliable, and stateful applications in a serverless environment. By combining orchestrator and activity functions with the power of the Durable Task Framework, developers can create elegant solutions for complex real-world problems.

For more detailed guidance, visit the Azure Durable Functions documentation.