Complete Guide to Azure Functions with Example, Step-by-Step Setup, and Interview Questions

🌟 What are Azure Functions?

Azure Functions is a serverless compute service provided by Microsoft Azure. It allows developers to run small pieces of code, called functions, without worrying about infrastructure.

Instead of setting up servers, scaling manually, or managing infrastructure, you only write the code, and Azure handles the rest.

👉 You pay only for execution time, making it cost-effective and scalable.

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🔧 Key Concepts in Azure Functions

• Trigger → Defines how the function starts (e.g., HTTP request, Timer, Queue, Blob upload).

• Input Binding → Brings data into the function.

• Output Binding → Sends processed data out (e.g., to CosmosDB, Storage, Service Bus).

📌 Example: An HTTP Trigger Function can process user input and save it to CosmosDB.

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🛠 Step-by-Step Example: Create an Azure Function

Let’s build a C# Azure Function that greets users.

1️⃣ Prerequisites

• An Azure subscription

• Visual Studio 2022 or VS Code with Azure Functions extension

• Azure Functions Core Tools (for CLI usage)

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2️⃣ Create a Function in VS Code

1. Open VS Code → Install Azure Functions Extension.

2. Click Azure Logo → Create New Project.

3. Select C# as language.

4. Choose HTTP trigger.

5. Name it GreetFunction.

6. Set Authorization level → Anonymous.

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3️⃣ Add Function Code

using System.IO;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;

public static class GreetFunction
{
    [FunctionName("GreetFunction")]
    public static IActionResult Run(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");

        string name = req.Query["name"];

        if (string.IsNullOrEmpty(name))
        {
            return new BadRequestObjectResult("Please pass a name in the query string.");
        }

        return new OkObjectResult($"Hello {name}, Welcome to Azure Functions!");
    }
}

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4️⃣ Run Locally

• Press F5 to run.

• Open browser:

  http://localhost:7071/api/GreetFunction?name=Cherry
  

• Output:

  Hello Cherry, Welcome to Azure Functions!
  

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5️⃣ Deploy to Azure

1. In VS Code → Right-click project → Deploy to Function App.

2. Select subscription & resource group.

3. Create a new Function App.

4. After deployment → Test the live URL:

   https://<yourappname>.azurewebsites.net/api/GreetFunction?name=Cherry
   

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6️⃣ Monitor & Logs

• In Azure Portal → Function App → Monitor,

• Track logs, execution count, and performance metrics.

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⚡ Real-World Use Cases of Azure Functions

• Image Processing → Triggered when a blob is uploaded.

• Email Notifications → Triggered by Queue messages.

• Scheduled Jobs → Using Timer Triggers (CRON).

• ETL Pipelines → Streaming data with Event Hub.

• IoT Applications → Processing telemetry events in real-time.

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🎯 Top Azure Functions Interview Questions

Basics

1. What are Azure Functions, and how do they differ from WebJobs?

2. Explain Triggers and Bindings.

3. What are the different hosting plans (Consumption, Premium, Dedicated)?

4. What is the cold start problem, and how do you reduce it?

5. Difference between Azure Functions and Azure Logic Apps.

Development & Deployment

6. How do you debug Azure Functions locally?

7. How can one Azure Function call another?

8. How do you secure Azure Functions? (API Keys, Azure AD, Managed Identity)

9. How do you manage secrets/configuration? (App settings, Azure Key Vault)

10. What is a Durable Function, and when should you use it?

Advanced

11. How do you monitor and log executions?

12. Can Azure Functions run in a VNET?

13. How does scaling work in Azure Functions?

14. How do retries work in queue-triggered functions?

15. What are Durable Entities in Azure Durable Functions?

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✅ Conclusion

Azure Functions is a powerful way to build event-driven, serverless applications on Azure.

• Easy to create with triggers and bindings.

• Cost-effective with pay-per-use pricing.

• Scales automatically with demand.

Whether you’re preparing for an interview or building real-world microservices, mastering Azure Functions gives you a strong edge in modern cloud development.

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