REST is great for exposing resources. But travel systems don't just exchange resources; they orchestrate time-sensitive transactions across unreliable external systems.
REST has become the default way to build APIs, and for good reason. It's simple, predictable, and works well for many common operations. But travel systems are rarely just simple request-response applications.
For example: A traveler searching for a flight. The system returns a seat for $420. Thirty seconds later, the traveler clicks Book, but the airline returns a different price, or the seat is no longer available.
These aren't unusual edge cases. They're fundamental characteristics of travel systems. Travel inventory is dynamic. Suppliers are distributed. Payments can be asynchronous. Booking workflows can involve multiple systems. And network failures are inevitable.
So the question isn't: Should we replace REST?, but "What communication patterns should we use when REST alone isn't enough?"
When REST alone falls short
There are three areas where relying entirely on synchronous REST calls can become problematic.
Real-time availability
Travel inventory is not static. Search results represent the state of availability at a particular moment, not a guarantee that the same inventory will still be available when the user books.
That's why booking systems often need to revalidate price and availability before confirming a transaction.
A typical flow becomes: Search → Select → Revalidate → Book
rather than simply: Search → Book
This extra validation helps prevent stale inventory from becoming a booking failure.
Long-running workflows
A booking may require several steps: Reservation → Payment → Ticketing → Confirmation
If all of these happen synchronously, the client may have to wait for multiple external systems to respond.
A better approach is to accept the request and process longer-running operations asynchronously. The API can return a booking ID and a processing status while background services continue the workflow.
This reduces the dependency between the user's request and the response time of external suppliers.
Third-party failures
Travel applications depend heavily on external APIs. Airlines, GDS platforms, hotel suppliers, and payment providers can all experience timeouts, rate limits, outages, or unexpected responses.
If every dependency is called synchronously, one failure can propagate through the entire booking flow.
This is where patterns such as timeouts, retries, circuit breakers, and asynchronous processing become essential.
Beyond request - response: webhooks, events, and async processing
Once a travel system needs to handle long-running processes and external events, it needs more than traditional request-response communication.
Webhooks
REST usually follows a simple pattern: your application asks another system for something.
But what happens when the external system has something to tell you?
For example, a payment provider may complete a transaction after the original request has finished. An airline may later update a flight schedule, or a supplier may confirm a booking.
Instead of repeatedly polling the external service, your application can receive these updates through webhooks.
Webhooks are useful for:
- Payment confirmations
- Booking status changes
- Flight updates
- Ticket issuance
- Supplier notifications
However, webhook processing needs to account for duplicate deliveries, retries, authentication, and events arriving out of order.
Events
Events are particularly useful for communication between internal services.
For example, when a booking is confirmed, the booking service can publish a BookingConfirmed event. Notification, analytics, loyalty, or customer-support services can consume that event independently.
This reduces direct dependencies between services and makes the architecture easier to scale.
Asynchronous processing
For operations that don't need to finish within a single HTTP request, background jobs and message queues can be used.
This is useful for supplier booking, ticket issuance, payment reconciliation, and notifications.
The principle is straightforward: Don't make the user wait synchronously for work that doesn't need to happen synchronously.
Two things travel APIs can't ignore: Idempotency & Resilience
Idempotency
Imagine a user submits a booking request. The airline successfully creates the reservation, but your application doesn't receive the response because of a network timeout.
From your application's perspective, the request failed. The user retries.
Without idempotency, the system could create a second booking.
An idempotency key allows the server to recognize that the retry belongs to an existing transaction and return the original result instead of processing the booking again.
Resilience
External dependencies will occasionally fail. A resilient travel system needs to handle those failures without taking down the entire application.
Common patterns include:
- Timeouts to prevent requests from hanging indefinitely
- Retries with exponential backoff for temporary failures
- Circuit breakers to stop repeatedly calling an unhealthy service
- Fallbacks when an alternative response or workflow is available
The goal isn't to make every external service perfectly reliable. It's to make sure that one unreliable dependency doesn't become a single point of failure for the entire booking system.
Designing a modern travel API: REST + Beyond
The answer isn't to replace REST. REST remains a strong choice for resource-oriented operations such as retrieving bookings, searching inventory, and accessing itineraries. The important part is knowing when another communication pattern is more appropriate.
The architecture should follow the behavior of the business operation, rather than forcing everything into synchronous request-response.
This matters particularly in travel because the system doesn't operate in isolation. It has to coordinate with suppliers that you don't control, work with inventory that changes constantly, and handle transactions that may span multiple services.
That's what makes travel API development different from building a typical CRUD application. A reliable travel API isn't simply an API that returns the right response when everything works.
It's an API that knows what to do when the price changes, the supplier times out, the payment succeeds but the response is lost, or the same request arrives twice.
Final thoughts
Travel APIs are not difficult simply because they have many endpoints. The real challenge is that they sit in the middle of a distributed ecosystem where inventory changes, external suppliers fail, and a single booking can involve multiple systems. REST remains an important foundation, but reliable travel platforms need more than synchronous request-response communication.
The right approach is to combine REST, webhooks, events, asynchronous processing, idempotency, and resilience patterns based on the requirements of each workflow.
Building a travel platform with Adamo Software
For travel businesses dealing with complex booking flows, supplier integrations, real-time inventory, and multi-channel distribution, architecture needs to be designed around the realities of the travel ecosystem.
Adamo Software builds custom travel software and booking platforms with integrations across GDS, NDC, and supplier APIs, with a focus on scalable and resilient travel operations.
