Modern businesses expect information to move quickly between applications.

An order is shipped, and the customer expects an update. Inventory changes, and the eCommerce platform needs accurate availability. A payment is processed, and the accounting system needs confirmation.

For organizations running IBM i, these requirements create an important integration question:

Should your applications use REST APIs, webhooks, or traditional polling to exchange information?

Each approach has advantages, and selecting the right one can affect performance, reliability, development effort, and long-term maintenance.

As organizations prepare their IBM i integration strategies for 2027, understanding the differences between IBM i webhooks and APIs can help teams build more responsive business processes without replacing existing RPG applications.

What Are IBM i Webhooks?

A webhook is an HTTP-based notification sent when a specific event occurs.

Instead of requiring another application to repeatedly request information, a webhook allows the originating system to notify a receiving application when something changes.

For example, an IBM i order management application might record that an order has shipped.

An integration component could then send a webhook notification to a connected customer portal.

The portal receives the event and updates the customer’s order status.

This approach can reduce the need for repeated requests when information has not changed.

Example: IBM i Shipment Notification

Consider a distribution company using IBM i to manage orders and shipping.

A webhook-enabled workflow might operate as follows:

1. An order is shipped in the IBM i application.
2. The RPG business process records the completed shipment.
3. An integration service identifies the shipment event.
4. A webhook sends the approved shipment information to the receiving application.
5. The customer portal updates the order status.
6. The delivery result is recorded for monitoring and troubleshooting.

The receiving application does not need to continuously ask whether the shipment status has changed.

Important: Webhook delivery requires appropriate application or integration logic. Existing RPG programs do not automatically generate webhooks simply because they run on IBM i.

What Is an IBM i REST API?

A REST API provides a standardized interface through which applications can request information or perform approved business operations.

For example, an eCommerce platform might call an IBM i API to retrieve current inventory availability.

The request could include a product identifier and warehouse location.

The IBM i application processes the request using existing business logic and returns the appropriate information.

REST APIs can support functions such as:

• Customer lookup
• Inventory availability
• Product pricing
• Order creation
• Shipment tracking
• Account information
• Invoice retrieval
• Business process automation

Unlike webhooks, which are commonly used to deliver event notifications, REST APIs typically operate through requests initiated by a consuming application.

This makes APIs particularly useful when an application needs information on demand.

IBM i Webhooks vs. REST APIs: What’s the Difference?

Although webhooks and REST APIs both commonly use HTTP, they serve different integration purposes.

Feature	REST APIs	Webhooks
Communication	Request initiated by a client	Notification initiated by an event
Primary purpose	Retrieve data or execute a function	Notify another system that something happened
Timing	When the client sends a request	When a configured event occurs
Typical use	Inventory lookup	Inventory change notification
Data exchange	Request and response	Event payload and delivery acknowledgment
Integration pattern	Request-driven	Event-driven
Reliability needs	Timeouts, error handling, retries	Delivery retries, deduplication, event tracking

Neither approach is automatically better.

The right choice depends on the business process.

For example, an application displaying inventory availability may need a REST API that retrieves current information.

A system notifying another application about an inventory adjustment may benefit from a webhook.

Many modern architectures use both approaches together.

What About Polling?

Polling is another common integration approach.

With polling, an application repeatedly checks another system for updated information.

For example, a customer portal might request order status every five minutes.

If the order has not changed, the API still receives and processes the request.

Polling can be simple to implement and may be appropriate when the source system does not support event notifications.

However, frequent polling can create unnecessary requests.

When Polling Makes Sense

Polling may remain appropriate when:

• Updates are relatively infrequent.
• Immediate notification is unnecessary.
• The source application cannot generate events.
• A receiving system requires periodic reconciliation.
• Simplicity is more important than immediate synchronization.

When Webhooks May Be Better

Webhooks can be useful when:

• Changes should trigger prompt notifications.
• Multiple applications need event updates.
• Repeated polling creates unnecessary traffic.
• Business processes depend on timely communication.
• The receiving application supports webhook endpoints.

The goal is not to eliminate polling everywhere.

It is to choose the most efficient and reliable communication method for each workflow.

1. Use REST APIs for On-Demand Business Information

REST APIs are particularly effective when applications need current information at the moment a user or process requests it.

Consider a sales representative using a mobile application.

Before confirming an order, the application may need to retrieve:

• Customer-specific pricing
• Available inventory
• Product information
• Credit status
• Delivery options

These requests should use approved IBM i business logic.

A REST API provides a consistent way to retrieve that information.

Why This Matters

Instead of copying business rules into the mobile application, IBM i can remain responsible for trusted calculations and processing.

This helps reduce duplicated logic while making existing applications accessible to modern platforms.

2. Use Webhooks for Business Event Notifications

Webhooks are especially useful when another system needs to know that something has happened.

Examples include:

• OrderCreated
• OrderShipped
• InventoryAdjusted
• CustomerUpdated
• PaymentReceived
• ProductionCompleted

Each event can initiate a downstream workflow.

For example, when an order ships, a webhook might notify a customer communication platform.

That platform could then send a shipping confirmation.

The IBM i application remains responsible for the transaction, while the connected application handles the customer communication.

3. Combine Webhooks and APIs for More Complete Workflows

One of the most effective integration patterns combines event notifications with on-demand API requests.

Consider a warehouse shipment process.

Step 1: IBM i records the shipment.

The RPG application completes the shipping transaction.

Step 2: A webhook notification is generated.

An integration service sends an event indicating that the order has shipped.

Step 3: The receiving application processes the notification.

The customer portal identifies the affected order.

Step 4: The portal requests additional information.

If needed, it calls an IBM i REST API to retrieve tracking details or current shipment status.

Step 5: The customer experience is updated.

The portal displays the latest information.

This approach combines the responsiveness of event notifications with the flexibility of APIs.

It can also keep webhook payloads relatively small by including only the information required to identify and process an event.

4. Preserve Existing RPG Business Logic

One of the biggest advantages of IBM i modernization is the ability to preserve trusted applications.

Organizations may already have RPG programs that manage:

• Inventory adjustments
• Order processing
• Pricing calculations
• Customer updates
• Financial transactions
• Production activities

These programs do not necessarily need to be rewritten to participate in modern integration workflows.

Instead, organizations can introduce appropriate interfaces around existing business functions.

For example, a shipment processing program could continue handling the core transaction while a separate integration component publishes a shipment event after successful completion.

Similarly, an existing RPG pricing routine could be exposed through a REST API.

The objective is to separate trusted business processing from the mechanisms used to communicate with other applications.

5. Consider Webhook Reliability Before Deployment

Webhooks can make integrations more responsive, but they also introduce reliability considerations.

What happens if the receiving application is unavailable?

What if a webhook is delivered twice?

What if events arrive out of order?

These situations should be addressed before deploying business-critical workflows.

Use Reliable Delivery Mechanisms

For important transactions, organizations should consider recording events durably before attempting delivery.

A persistent event queue or transactional outbox pattern can help ensure that events are not lost if the receiving system is temporarily unavailable.

Implement Controlled Retries

Failed deliveries may need to be retried.

However, retries should use appropriate limits and delays to avoid overwhelming the receiving application.

Prevent Duplicate Processing

Webhook consumers should be designed to handle duplicate notifications.

A unique event identifier can help the receiving application determine whether an event has already been processed.

Monitor Delivery Status

Teams should be able to determine:

• When an event was generated
• Which endpoint received it
• Whether delivery succeeded
• Whether retries occurred
• Whether manual intervention is required

Reliable event delivery is just as important as fast event delivery.

6. Secure IBM i Webhook Integrations

Webhooks and APIs both require appropriate security controls.

Webhook endpoints should not automatically trust incoming requests simply because they appear to originate from a known application.

Organizations should consider:

• HTTPS encryption
• Request authentication
• Payload signatures
• Timestamp validation
• Replay protection
• Least-privilege permissions
• Input validation
• Secure credential storage
• Activity logging

For example, a webhook receiver may verify a cryptographic signature before processing an event.

The receiving system should also validate the payload and ensure the requested operation is authorized.

Sensitive customer or financial information should not be included in webhook payloads unless required and appropriately protected.

7. Understand the Performance Implications

REST APIs, webhooks, and polling can create different workload patterns.

REST APIs

Performance depends on factors such as:

• Request volume
• RPG processing time
• Db2 for i query efficiency
• Network latency
• Concurrent connections

Webhooks

Performance considerations include:

• Event generation
• Queue processing
• Delivery time
• Receiving application capacity
• Retry behavior
• Event volume

Polling

Performance depends on:

• Polling frequency
• Number of consumers
• Database query cost
• Percentage of requests returning unchanged information

An integration architecture should be evaluated using realistic business workloads.

For example, a high-volume inventory process may generate many events in a short period.

That workload may require batching, queueing, or other controls to prevent downstream systems from becoming overwhelmed.

Related Reading: IBM i API Performance Optimization: 8 Best Practices for Faster, More Reliable Integrations

8. Build an Integration Strategy Around Business Requirements

Technology selection should begin with the business process.

Before choosing a webhook, REST API, or polling model, ask:

How quickly does the information need to move?

Does the receiving application need immediate notification, or is a periodic update sufficient?

Who initiates the communication?

Does an application request information, or does a business event trigger an action?

What happens if delivery fails?

Can the process be retried, or does it require immediate intervention?

How much information is required?

Should the notification contain a complete record or only an event identifier?

How many applications need the information?

Would a reusable API or event distribution mechanism provide greater long-term value?

These questions help organizations select integration methods based on business outcomes rather than technology trends.

Where Kato Integrations Fits into Modern IBM i Connectivity

Kato Integrations focuses on simplifying how organizations connect IBM i applications with modern technologies.

Through RPG API Express, IBM i developers can build and consume web services using RPG, including REST and SOAP integrations and JSON and XML data.

This can provide a foundation for workflows that need to call external APIs, expose existing business functions, or connect RPG applications with cloud-based services.

For webhook-driven workflows, organizations should evaluate the additional event detection, outbound delivery, retry, and monitoring components required for their specific implementation.

Kato’s RPG-based integration approach can help organizations keep existing development expertise involved in modernization without automatically introducing a completely separate application development stack.

Kato also provides professional services for organizations requiring additional IBM i integration expertise.

A Practical IBM i Integration Roadmap for 2027

Organizations do not need to replace every existing integration at once.

A phased approach can reduce risk while improving connectivity.

Phase 1: Inventory Existing Integrations

Identify:

• REST APIs
• SOAP services
• File transfers
• Scheduled jobs
• Polling processes
• Custom interfaces
• Manual workflows

Document their purpose, ownership, dependencies, and business importance.

Phase 2: Identify Time-Sensitive Processes

Look for processes where delayed information creates operational problems.

Examples include:

• Order status
• Inventory availability
• Shipment notifications
• Customer updates
• Payment events

Phase 3: Select the Right Integration Pattern

Determine whether each workflow is best supported by:

• On-demand REST APIs
• Event-driven webhook notifications
• Scheduled polling
• Batch processing
• A combination of these approaches

Phase 4: Establish Security and Reliability Standards

Define:

• Authentication
• Authorization
• Event identification
• Retry policies
• Error handling
• Monitoring
• Documentation

Phase 5: Start with a Controlled Pilot

Choose one manageable business process.

Shipment notifications or customer-status updates may provide useful starting points.

Phase 6: Measure the Results

Track improvements in:

• Processing time
• Manual effort
• Integration reliability
• Request volume
• Data accuracy
• Customer experience

Use the results to determine which additional integrations should be modernized.

Frequently Asked Questions About IBM i Webhooks and APIs

Can IBM i use webhooks?

Yes. IBM i applications can participate in webhook workflows through appropriately designed RPG programs, HTTP clients, event detection, or integration services that send and receive HTTP notifications.

What is the difference between IBM i webhooks and REST APIs?

REST APIs generally allow applications to request information or perform approved operations. Webhooks typically notify another application when a predefined event occurs.

Are webhooks faster than polling?

Webhooks can reduce notification delays because they send updates when events occur rather than waiting for the next polling interval. Actual performance depends on delivery infrastructure and system availability.

Can RPG programs trigger webhooks?

Yes. RPG applications can initiate or participate in outbound HTTP workflows using suitable integration tools or services. The implementation must handle event detection, request delivery, errors, and security.

Do webhooks replace REST APIs?

No. Webhooks and REST APIs often complement each other. A webhook may notify an application that something changed, while an API provides the detailed information needed afterward.

Are webhooks reliable for business-critical transactions?

They can be when implemented with durable event recording, controlled retries, duplicate detection, monitoring, and appropriate recovery procedures.

Should IBM i organizations eliminate polling?

Not necessarily. Polling remains appropriate for some workloads, especially when event notifications are unavailable or immediate synchronization is unnecessary.

Does IBM i need to move to the cloud to support webhooks?

No. IBM i can remain on-premises, hosted, or part of a hybrid environment while securely communicating with external applications through approved integration services.

Final Thoughts

Modern IBM i integration is not about choosing one technology for every business process.

It is about selecting the right communication method for the information being exchanged.

REST APIs provide controlled, on-demand access to business capabilities.

Webhooks help notify connected applications when important events occur.

Polling remains useful when periodic checks are appropriate.

Together, these approaches can create a flexible integration architecture that supports cloud connectivity, automation, eCommerce, mobile applications, and future AI initiatives.

For IBM i organizations preparing for 2027, the opportunity is to build more responsive workflows while preserving the RPG applications and business logic that continue to deliver value.

The goal isn’t simply to move data faster. It’s to make sure the right systems receive the right information at the right time.