Azure Functions

Azure Functions: Complete Guide for Developers and Solution Architects

Azure Functions is one of Microsoft's most powerful serverless offerings. It enables developers to run code on demand without worrying about infrastructure, servers, operating systems, patching, or scaling.

In this article, I summarize everything I learned about Azure Functions while building and deploying Java-based functions integrated with Azure API Management (APIM), Microsoft Entra ID, and Microsoft Graph.

What is Azure Function?

Azure Functions is a serverless compute service that allows developers to execute code in response to events without managing infrastructure.

Microsoft automatically handles:

• Server provisioning
• Operating system management
• Patching
• Scaling
• Availability
• Monitoring

Developers can focus entirely on writing business logic.

Traditional Application

Application
     ↓
Virtual Machine
     ↓
Operating System
     ↓
Infrastructure

Managed by Developer

Azure Function

Application
     ↓
Azure Functions Platform

Managed by Azure

Why Use Azure Functions?

1. Serverless Computing

No virtual machines need to be managed. Developers deploy code and Azure executes it automatically.

2. Automatic Scaling

10 Requests
      ↓
1 Function Instance

1000 Requests
      ↓
Multiple Function Instances

Scaling happens automatically.

3. Pay for What You Use

On Consumption and Flex Consumption plans:

• No requests = No cost
• Pay only when code executes

4. Event Driven Architecture

Functions execute when specific events occur.

Event
   ↓
Azure Function
   ↓
Business Logic

Common Azure Function Use Cases

• REST APIs
• Graph API integrations
• File processing
• Scheduled jobs
• Background processing
• Data transformations
• Service Bus consumers
• Microservice components
• Webhook endpoints
• IoT processing

Types of Azure Function Triggers

Every Azure Function starts with a trigger. A trigger defines what causes the Function to execute.

1. HTTP Trigger

Most commonly used trigger.

Browser
   ↓
HTTP Request
   ↓
Azure Function

Java Example:

@HttpTrigger(
    name = "req",
    methods = {HttpMethod.GET, HttpMethod.POST},
    authLevel = AuthorizationLevel.ANONYMOUS
)

Use Cases:

• REST APIs
• Webhook endpoints
• Authentication services
• Microservices

2. Timer Trigger

Schedule
   ↓
Azure Function

Example:

Every Day 2 AM

Use Cases:

• Nightly processing
• Reports
• Cleanup jobs
• Data synchronization

3. Blob Trigger

Blob Uploaded
      ↓
Azure Function

Use Cases:

• Image processing
• PDF processing
• File validation

4. Queue Trigger

Storage Queue
       ↓
Azure Function

Use Cases:

• Asynchronous processing
• Decoupled systems

5. Service Bus Trigger

Azure Service Bus
         ↓
Azure Function

Use Cases:

• Enterprise integrations
• Microservices
• Event driven systems

6. Event Grid Trigger

Resource Event
      ↓
Event Grid
      ↓
Azure Function

7. Cosmos DB Trigger

Document Updated
        ↓
Azure Function

8. Event Hub Trigger

IoT Events
     ↓
Event Hub
     ↓
Azure Function

Azure Function Hosting Plans

Consumption Plan

Classic serverless model.

No Requests
      ↓
Scale to Zero

Flex Consumption Plan

New generation serverless hosting plan.

Benefits:

• Faster startup times
• Improved networking support
• Enhanced scaling

Premium Plan

For enterprise workloads.

Benefits:

• No cold starts
• VNET Integration
• Higher throughput

App Service Plan

Dedicated infrastructure.

App Service Plan
      ↓
Azure Function

Ways to Develop Azure Functions

Visual Studio Code

Most popular choice.

Extensions:

• Azure Functions Extension
• Azure Tools Extension

Visual Studio

Best for .NET Developers.

IntelliJ IDEA

Popular among Java developers.

Maven

Common approach for Java Azure Functions.

mvn azure-functions:run

Ways to Deploy Azure Functions

1. Azure Portal

Manual deployment through Azure Portal. Useful for experiments and proofs of concept.

2. VS Code Deployment

Right Click Function App
       ↓
Deploy

3. Maven Deployment

mvn azure-functions:deploy

Preferred deployment method for Java projects.

4. ZIP Deployment

az functionapp deployment source config-zip

Useful for scripted deployments.

5. Azure CLI Deployment

az functionapp create
az functionapp deploy

6. GitHub Actions

GitHub
    ↓
Build
    ↓
Deploy
    ↓
Azure Function

7. Azure DevOps Pipelines

Build Pipeline
      ↓
Release Pipeline
      ↓
Azure Function

8. Terraform

Infrastructure as Code deployment.

Ways to Test Azure Functions Locally

1. Azure Functions Core Tools

func start

or

mvn azure-functions:run

2. Browser Testing

For GET requests:

http://localhost:7071/api/HttpExample?name=Vikas

3. Curl

curl "http://localhost:7071/api/HttpExample?name=Vikas"

4. Postman

Most common testing tool.

5. Bruno

Lightweight API testing tool.

6. VS Code Debugger

Supports breakpoints and step-by-step debugging.

7. Unit Testing

JUnit
Mockito

Useful for testing business logic.

My Java Azure Function Example

I built and deployed the following Java Azure Function.

@FunctionName("HttpExample")
public HttpResponseMessage run(
    @HttpTrigger(
        name = "req",
        methods = {HttpMethod.GET, HttpMethod.POST},
        authLevel = AuthorizationLevel.ANONYMOUS)
        HttpRequestMessage<Optional<String>> request,
    final ExecutionContext context) {

    final String query =
        request.getQueryParameters().get("name");

    final String name =
        request.getBody().orElse(query);

    if (name == null) {
        return request.createResponseBuilder(
            HttpStatus.BAD_REQUEST)
            .body("Please pass a name")
            .build();
    }

    return request.createResponseBuilder(
        HttpStatus.OK)
        .body("Hello, " + name)
        .build();
}

Testing Through Browser

Once deployed, the Function can be called through a browser.

https://myfunction.azurewebsites.net/api/HttpExample?name=Vikas

Response:

Hello, Vikas

Calling Azure Function Using Postman

GET Request Example

Method:

GET

URL:

https://myfunction.azurewebsites.net/api/HttpExample?name=Vikas

Response:

Hello, Vikas

POST Request Example

Method:

POST

Headers:

Content-Type: text/plain

Body:

Vikas

Calling Azure Function Using Bearer Tokens

I also built a Function that accepts Authorization headers.

Authorization: Bearer eyJ...

The Function:

• Receives the JWT token
• Decodes the token
• Extracts the App ID claim
• Calls Microsoft Graph

Calling Azure Function Through APIM

One interesting scenario I implemented was:

Client
   ↓
Azure API Management
   ↓
Azure Function
   ↓
Microsoft Graph

APIM policy:

<send-request
    mode="new"
    response-variable-name="userContext">

    <set-url>
        https://myfunction.azurewebsites.net/api/ValidateApp
    </set-url>

    <set-method>POST</set-method>

    <set-header
        name="Authorization"
        exists-action="override">

        <value>
            @(context.Request.Headers
              .GetValueOrDefault("Authorization"))
        </value>

    </set-header>

</send-request>

Key Benefits of Azure Functions

• No infrastructure management
• Serverless architecture
• Automatic scaling
• Rapid development
• Low operational cost
• Strong Azure integration
• Easy API creation
• Event-driven processing
• Supports Java, .NET, Python, Node.js, and PowerShell

Key Learnings

• Azure Functions are ideal for event-driven workloads.
• Java Azure Functions are straightforward to develop and deploy.
• Azure Functions integrate seamlessly with APIM.
• Bearer tokens can be passed through APIM to Functions.
• Microsoft Graph can be called from Functions for advanced authorization patterns.
• Managed Identity is the preferred authentication mechanism for Azure services.
• Functions are excellent building blocks for microservices and integration solutions.

Conclusion

Azure Functions provide a modern serverless platform for building APIs, integrations, automation, and event-driven workloads. Developers can focus on business logic while Azure manages infrastructure, scaling, availability, and operations.

Whether you are building REST APIs, integrating Microsoft Graph, processing files, or implementing enterprise authorization solutions behind APIM, Azure Functions provide a powerful and cost-effective way to deliver cloud-native applications.