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⚡ Azure Functions — Short Notes for Interview

Azure Functions is a serverless compute service in Azure. You write code, and Azure runs it automatically whenever an event triggers it. No need to manage servers or infrastructure.

🟢 1. What is Azure Function?

  • Serverless → pay only for execution time, no VM management.
  • Runs small units of code ("functions") in response to triggers.
  • Supports multiple languages (C#, JavaScript, Python, Java, PowerShell, etc.).

🟢 2. Key Concepts

  • Function App → Container for one or more functions (like a project).
  • Trigger → Event that starts a function (HTTP request, Timer, Blob, Queue, Event Hub, etc.).
  • Binding → Way to connect to other services without boilerplate code.
    • Input Binding: brings data into function.
    • Output Binding: sends data from function.
  • Consumption Plan → Auto-scales and pay-per-use.
  • Premium/Dedicated Plan → Pre-warmed instances, VNET support, higher performance.

🟢 3. Types of Triggers

  • HTTP Trigger → run on API calls.
  • Timer Trigger → run on schedule (CRON).
  • Blob Trigger → run when file uploaded/modified in Blob Storage.
  • Queue Trigger → run when message is added to Azure Storage Queue.
  • Event Hub / Service Bus Trigger → run on event/message arrival.
  • Cosmos DB Trigger → run when document changes in Cosmos DB.

🟢 4. Example: HTTP Trigger (C#)

[FunctionName("HelloFunction")]
public static IActionResult Run(
    [HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger executed.");
    string name = req.Query["name"];
    return new OkObjectResult($"Hello {name}");
}

👉 Call: https://<function-app>.azurewebsites.net/api/HelloFunction?name=Tushar

🟢 5. Authorization Levels

  • Anonymous → No key required.
  • Function → Requires function key.
  • Admin → Master key required.
  • Supports Azure AD / Entra ID authentication.

🟢 6. Durable Functions (Stateful Workflows)

  • Built on top of Azure Functions.
  • Lets you write stateful workflows in code.
  • Patterns supported:
    • Function chaining (A → B → C)
    • Fan-out/Fan-in (parallel tasks then aggregate)
    • Human interaction (wait for external input)

🟢 7. Monitoring & Logging

  • Integrated with Application Insights.
  • Tracks execution time, failures, dependencies.

🟢 8. Best Practices

  • Keep functions small and single responsibility.
  • Use retry policies for transient errors.
  • Handle exceptions & logging properly.
  • Choose right hosting plan based on workload.
  • Secure secrets with Azure Key Vault.
  • Version your APIs (for HTTP functions).

🟢 9. Pros & Cons

✅ Pros:

  • Auto scaling, pay-per-use.
  • Easy integration with Azure services.
  • Event-driven, quick to build APIs.

❌ Cons:

  • Cold start latency (Consumption plan).
  • Limited execution time in consumption (5–10 min).
  • Vendor lock-in (Azure specific).

🟢 10. Common Interview Questions

  1. What are triggers and bindings in Azure Functions?
  2. Difference between Consumption, Premium, and Dedicated plans?
  3. How do you secure an HTTP-triggered function?
  4. Explain Durable Functions with a use case.
  5. How do you monitor failures in Azure Functions?
  6. How do you handle configuration and secrets securely?
  7. Difference between Azure Functions and Azure Logic Apps?
  8. What is a cold start? How to reduce it?

✅ Quick Recap for Interview:

  • Azure Function = serverless event-driven code.
  • Key building blocks → Triggers + Bindings.
  • Supports many triggers (HTTP, Timer, Blob, Queue, Cosmos, Event Hub).
  • Plans → Consumption (pay-per-use), Premium (no cold start), Dedicated (App Service plan).
  • Durable Functions → Orchestration + workflows.


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