Introduction

When you build modern applications—whether it’s fintech, eCommerce, SaaS platforms, or internal enterprise systems—your app must talk to other systems. And as a .NET developer, you’ll repeatedly encounter two integration patterns:

• APIs
• Webhooks

Both allow systems to communicate, but they serve completely different purposes.

Despite being simple concepts, both are deeply misunderstood by junior developers. Even in interviews, many candidates fail to explain the exact difference between them—not because they don’t know them, but because they don’t understand how they behave under load, how they affect architecture, or why real-time systems prefer one over the other.

This guide fixes that.

In this in-depth article, we’ll compare Webhooks vs APIs from a developer perspective, explore how data flows, how to design real systems using them, and finally, how to implement real-time data export to SQL Server using Webhooks in ASP.NET Core.

What is an API?

API stands for Application Programming Interface.
Think of APIs as the “Request → Response” model of communication.

You ask.
The server answers.
That’s it.

Simple Analogy

Imagine you’re hungry.
You call the restaurant and ask:

“Is my order ready?”

They check the kitchen and reply:

“Not yet.”

Two minutes later, you call again:
“Is it ready now?”

This is how APIs work.

You repeatedly pull information by making API calls.

How APIs Work (Technical Explanation)

When your application needs data, it makes an HTTP request such as:

GET /api/orders/123
POST /api/login
PUT /api/users/update

GET /api/orders/123
POST /api/login
PUT /api/users/update

The server processes the request and sends back JSON/XML/etc.

API Workflow

Client → sends request → API Server → processes → returns response

Client → sends request → API Server → processes → returns response

This is synchronous or asynchronous, depending on implementation, but always client-initiated.

When APIs Are Useful

APIs are best for:

• Fetching data on demand
• Filtering or searching data
• CRUD operations
• User actions (login, update, delete)
• When frequency of data access is moderate
• When you need dynamic requests

Examples:

• Get all products
• Fetch weather data
• Get student details
• Search jobs
• Validate user login

API Limitations

The biggest issue with APIs:

The Server Does NOT Push Data

The server never calls you back.
You have to ask again and again, known as:

Polling

Polling = repeatedly calling API to check if something changed.

Example:

If you call an API every 1 minute:

1440 API calls per day

1440 API calls per day

For 1,000 users, this becomes:

1,440,000 API calls/day

1,440,000 API calls/day

⚠️ This increases:

• API load
• Server cost
• Network usage
• Rate limit issues

Most real-time data requirements fail with polling.

What is a Webhook? (The Push-Based Event Model)

A Webhook is a server-to-server automatic callback.

The moment something happens, the other system pushes the data to you.

Analogy

This time, the restaurant calls you:

“Your order is ready. You can pick it up now.”

You didn’t call them at all.

This is how Webhooks work.

How Webhooks Work (Technical Explanation)

A Webhook provider sends an HTTP POST request to your endpoint when an event occurs.

Webhook Workflow

Event occurs in remote system
↓
Webhook triggers
↓
Sends POST request to your API endpoint
↓
Your system processes the data
↓
You respond with 200 OK

Event occurs in remote system
↓
Webhook triggers
↓
Sends POST request to your API endpoint
↓
Your system processes the data
↓
You respond with 200 OK

Everything happens instantly, automatically, without any polling.

When Webhooks Are Useful

Webhooks are perfect when you need real-time integration, especially:

✔ Payment success (Stripe, Razorpay, PayPal)
✔ Order creation (Shopify, WooCommerce)
✔ Code push (GitHub/Bitbucket)
✔ Lead creation (HubSpot, Zoho CRM)
✔ Ticket creation (Zendesk, Freshdesk)
✔ SMS delivery reports
✔ IoT event updates

Any event-driven system uses Webhooks.

Webhook Limitations

Webhooks require:

❌ Public endpoint
❌ SSL certificate
❌ More complex debugging
❌ Handling of retries
❌ Signature validation for security

But…
For real-time systems → Webhooks win totally.

Webhooks vs APIs: Technical Comparison for Developers

Below is a developer-grade comparison table:

Why Webhooks Are Better for Real-Time SQL Export

Your manager asked you:

“Export real-time data to SQL using Webhooks in ASP.NET.”

Here’s why Webhooks are perfect for this.

API Approach: Why It Fails

Imagine you call API every minute to check new data.

Problems:

❌ Too many requests
❌ High cost
❌ No true real-time
❌ Rate limits
❌ Possible data duplication

For 10,000 records per day, polling becomes a nightmare.

Webhook Approach: Perfect Solution

Webhook pushes ONLY when new data arrives.

✔ No polling
✔ No wasted bandwidth
✔ Real-time inserts
✔ Low cost
✔ Scalable
✔ Perfect for event-driven SQL insert

Architecture: Real-Time Data Push to SQL Using Webhooks (ASP.NET Core)

Here is the full system design explained simply:

5.1 High-Level Architecture (Text Diagram)

External System (Provider)
       │
       ▼
Webhook POST Request
       │
       ▼
ASP.NET Core API Endpoint (/webhook/data)
       │
       ▼
DTO Model Binding
       │
       ▼
Data Validation + Signature Check
       │
       ▼
Background Queue / Hosted Service
       │
       ▼
SQL Server Insert
       │
       ▼
Response 200 OK

External System (Provider)
       │
       ▼
Webhook POST Request
       │
       ▼
ASP.NET Core API Endpoint (/webhook/data)
       │
       ▼
DTO Model Binding
       │
       ▼
Data Validation + Signature Check
       │
       ▼
Background Queue / Hosted Service
       │
       ▼
SQL Server Insert
       │
       ▼
Response 200 OK

5.2 Why Background Queue is Important

If your webhook performs heavy processing directly:

❌ Response is delayed
❌ Provider may retry
❌ Performance issues

Best practice:

✔ Receive instantly
✔ Acknowledge
✔ Process in background

ASP.NET Core has:

• BackgroundService
• Channel Queue
• Hangfire
• Azure Queue
• MassTransit
• Kafka (advanced)

.NET 8 / .NET 9 Webhook Implementation (Step-by-Step)

Now let’s write production-ready, senior-level code.

Step 1 — Create Controller

[ApiController]
[Route("webhook")]
public class WebhookController : ControllerBase
{
    private readonly IBackgroundTaskQueue _queue;

    public WebhookController(IBackgroundTaskQueue queue)
    {
        _queue = queue;
    }

    [HttpPost("data")]
    public async Task<IActionResult> Receive([FromBody] WebhookPayload payload)
    {
        if (payload == null)
            return BadRequest();

        // Signature validation (optional example)
        var signature = Request.Headers["X-Signature"].ToString();
        if (!SignatureValidator.IsValid(payload, signature))
            return Unauthorized();

        // Add to background queue
        await _queue.QueueBackgroundWorkItemAsync(async token =>
        {
            await ProcessWebhookAsync(payload);
        });

        return Ok(new { status = "received" });
    }
}

[ApiController]
[Route("webhook")]
public class WebhookController : ControllerBase
{
    private readonly IBackgroundTaskQueue _queue;

    public WebhookController(IBackgroundTaskQueue queue)
    {
        _queue = queue;
    }

    [HttpPost("data")]
    public async Task<IActionResult> Receive([FromBody] WebhookPayload payload)
    {
        if (payload == null)
            return BadRequest();

        // Signature validation (optional example)
        var signature = Request.Headers["X-Signature"].ToString();
        if (!SignatureValidator.IsValid(payload, signature))
            return Unauthorized();

        // Add to background queue
        await _queue.QueueBackgroundWorkItemAsync(async token =>
        {
            await ProcessWebhookAsync(payload);
        });

        return Ok(new { status = "received" });
    }
}

Step 2 — Create DTO Model

public class WebhookPayload
{
    public string EventType { get; set; }
    public DateTime Timestamp { get; set; }
    public OrderData Data { get; set; }
}

public class OrderData
{
    public string OrderId { get; set; }
    public string Customer { get; set; }
    public decimal Amount { get; set; }
}

public class WebhookPayload
{
    public string EventType { get; set; }
    public DateTime Timestamp { get; set; }
    public OrderData Data { get; set; }
}

public class OrderData
{
    public string OrderId { get; set; }
    public string Customer { get; set; }
    public decimal Amount { get; set; }
}

Step 3 — Background Task Queue

public interface IBackgroundTaskQueue
{
    ValueTask QueueBackgroundWorkItemAsync(Func<CancellationToken, Task> workItem);
    ValueTask<Func<CancellationToken, Task>> DequeueAsync(CancellationToken cancellationToken);
}

public interface IBackgroundTaskQueue
{
    ValueTask QueueBackgroundWorkItemAsync(Func<CancellationToken, Task> workItem);
    ValueTask<Func<CancellationToken, Task>> DequeueAsync(CancellationToken cancellationToken);
}

Step 4 — SQL Insert Logic

private async Task ProcessWebhookAsync(WebhookPayload payload)
{
    using var conn = new SqlConnection(_config.GetConnectionString("Default"));
    await conn.OpenAsync();

    var query = "INSERT INTO Orders (OrderId, Customer, Amount, Timestamp) VALUES (@Id, @Cust, @Amt, @Time)";

    await conn.ExecuteAsync(query, new
    {
        Id = payload.Data.OrderId,
        Cust = payload.Data.Customer,
        Amt = payload.Data.Amount,
        Time = payload.Timestamp
    });
}

private async Task ProcessWebhookAsync(WebhookPayload payload)
{
    using var conn = new SqlConnection(_config.GetConnectionString("Default"));
    await conn.OpenAsync();

    var query = "INSERT INTO Orders (OrderId, Customer, Amount, Timestamp) VALUES (@Id, @Cust, @Amt, @Time)";

    await conn.ExecuteAsync(query, new
    {
        Id = payload.Data.OrderId,
        Cust = payload.Data.Customer,
        Amt = payload.Data.Amount,
        Time = payload.Timestamp
    });
}

Webhook Security: Must-Know Concepts for Developers

Webhook security is often ignored by juniors. In real enterprises, it’s not optional.

Signature Validation

The provider will generate a hash:

HMAC_SHA256(body + secret)

HMAC_SHA256(body + secret)

You verify it on your end.

IP Whitelisting

Only accept requests from specific provider IP ranges.

HTTPS Only

No HTTP allowed for production.

Retry Logic Awareness

Webhook providers retry when your endpoint fails.

Example:

1 minute → 5 minutes → 30 minutes → 1 hour

1 minute → 5 minutes → 30 minutes → 1 hour

So your code must be idempotent.

Webhooks vs APIs: Real-World Use Cases in Enterprises

API Use Cases

✔ Login
✔ Fetching details
✔ Uploading data
✔ Searching data
✔ Pagination queries

Webhook Use Cases

✔ Payment success
✔ Shipment updates
✔ Stock alerts
✔ SMS delivery reports
✔ Workflow automation
✔ Lead creation

Performance Comparison (Under Load)

Scenario: 10,000 updates per day

API

• Poll every 30 seconds
• 2880 calls/day per user
• Server crash risk
• Rate limits
• High cost

Webhook

• Only 10,000 events
• Near 0 wasted calls
• Super scalable

Interview-Cracker Explanation (For Developers)

If asked in an interview:

“Explain API vs Webhook.”

Say this:

APIs are pull-based request-response operations where the client asks for data, while Webhooks are push-based event notifications where the server sends data automatically when something happens. APIs are good for CRUD operations and fetching data on demand, while Webhooks are ideal for real-time event-driven systems like payments, order updates, or notifications.

Conclusion

Both APIs and Webhooks are essential tools for modern software systems.
But they serve different purposes.

• Use APIs when your system needs data on demand.
• Use Webhooks when your system needs automatic real-time updates.

For your requirement—exporting real-time data to SQL through Webhooks in ASP.NET Core—Webhooks are the best and only scalable solution.

Your system becomes:

✔ Real-time
✔ Efficient
✔ Scalable
✔ Cost-effective
✔ Enterprise-ready

Let’s Connect 

I hope this article about interview Questions on delegates in ASP.NET Core helps you grow in your .NET developer interview in 2025 and beyond. I regularly share coding resources, learning roadmaps, project ideas, and career tips across multiple platforms. If you found this helpful, consider following me and joining the Logic Lense community!

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