Hey there! If you’ve ever dabbled in building APIs, you’ve probably hit that moment of confusion: How many APIs should I actually create? It’s a question that pops up all the time, especially when you’re dealing with features that seem kind of similar. Do you mash them into one endpoint or split them up? It’s not always clear, and honestly, there’s no one-size-fits-all answer. But don’t worry—I’m here to break it down in a way that’s easy to follow, with real-world examples to make sense of it all. By the end of this, you’ll have a solid grip on how to decide whether to go with one endpoint for multiple services or give each service its own. Let’s dive in!
The Big Question: One API or Many?
When you’re building something like a microservices architecture, this question comes up a lot: Should I create a single API that handles a bunch of services, or should each service have its own dedicated API? To unpack this, let’s start with a scenario that’s pretty common.
Imagine you’re working on a website with two main features: one for booking hotels and another for selling products, like an online store. Both services involve purchases, and both need a way to handle refunds. So, when it comes to creating the refund API, what’s the best move? Do you build one endpoint that can handle refunds for everything—hotels, products, maybe even flight tickets if you add those later? Or do you create separate refund endpoints for each service, even if it means more work upfront?
This is where things get interesting. The answer depends on a few factors, but the big one is domains. No, I’m not talking about website URLs like www.something.com. I mean business domains—the distinct areas of functionality in your system. Let’s explore this idea with our hotel and product example and see how it plays out.
Understanding Domains in Microservices
In the world of microservices, a domain is like a boundary around a specific part of your business. It’s a way to group related features and logic together. In our example, hotel bookings and product sales feel like two separate domains. Why? Because even though both involve purchases and refunds, the way they work is fundamentally different.
- Hotel Booking Domain: This is all about reserving rooms, checking availability, dealing with check-in dates, and maybe handling cancellations or no-show policies. A refund here might involve coordinating with a hotel partner or adjusting a booking status.
- Product Sales Domain: This is more about inventory, shipping, and retail logistics. A refund might mean restocking an item, issuing a return label, or handling a damaged product.
Sure, both domains have purchases and refunds, but the processes, data, and even the teams managing them are likely different. That’s a clue that they might need separate APIs.
To make this clearer, think about an online store with buyers and sellers. Both can search for products, right? A buyer searches to find something to buy, and a seller searches to check their listings. The feature sounds similar, but the context is different. Buyers and sellers operate in distinct domains, so you’d probably want separate APIs for their search functionality—one for the buyer domain and one for the seller domain.
Case Study: Two Domains, Two APIs
Let’s stick with our hotel booking and product sales example. If I had to make a call, I’d lean toward creating two separate endpoints for refunds: one for hotel bookings and one for product sales. Here’s why.
Why Separate Endpoints?
- Different Domains, Different Logic
Hotel refunds and product refunds might share some similarities (like updating a payment status), but the details diverge. For hotels, you might need to check room availability or cancel a reservation with a third-party provider. For products, you’re dealing with inventory updates or return shipping. Combining these into one endpoint could lead to a messy, complex codebase with lots of if-else conditions to handle each case. That’s a recipe for bugs and headaches down the road. - Team Ownership
In most companies, different teams handle different domains. You might have a hotel product team focused on bookings and a retail product team focused on sales. If you force both teams to share a single refund endpoint, you’re creating a dependency between them. Every time one team needs to tweak the refund logic, they’ll have to coordinate with the other. Separate endpoints keep things clean—each team owns its API and can work independently. - Scalability
Microservices are all about breaking things into smaller, independent pieces. If hotel bookings suddenly explode in popularity (say, during a holiday season), you don’t want the refund endpoint for products to get bogged down because it’s handling both. Separate endpoints let you scale each service on its own terms. - Clearer Contracts
An API is like a contract between the backend and the frontend (or other services). A single refund endpoint that handles everything might need a super generic payload, like "type": "hotel" or "type": "product", to figure out what’s being refunded. That’s not very intuitive. With separate endpoints, you can design specific payloads tailored to each domain, making it easier for developers to understand and use.
So, in this case, you’d end up with something like:
- POST /hotel-service/orders/{id}/refund for hotel bookings
- POST /retail-service/orders/{id}/refund for product sales
Each endpoint is focused, handling just one domain’s refund process. The hotel team can optimize their refund logic without worrying about breaking the retail team’s flow, and vice versa.
When to Use One API: The Same-Domain Case
Now, let’s flip the script. There are times when combining multiple services into a single API makes sense. The key is when they’re part of the same domain. To illustrate, let’s look at a different example: a payment gateway.
Imagine you’re building a payment service that supports multiple methods—credit cards, internet banking, bank transfers, and digital wallets like GoPay or Dana. Each method is different under the hood:
- Credit card payments might involve tokenizing a card and sending it to a bank.
- Internet banking could mean redirecting to a bank’s login page.
- Bank transfers might require generating a unique virtual account number.
- Digital wallets involve APIs for services like GoPay or Dana.
At first glance, you might think, Wow, these are so different—maybe I need separate APIs for each! But hold on. All these methods belong to the same payment domain. They’re different flavors of the same core function: processing a payment. In this case, it makes sense to create a single endpoint, like:
- POST /payment-service/payments
Here’s how it works. The request body includes a type field to specify the payment method, like:
{
"amount": 100000,
"type": "credit_card",
"card_number": "1234-5678-9012-3456",
"expiry_date": "12/26",
"cvv": "123"
}Or for internet banking:
{
"amount": 100000,
"type": "internet_banking",
"bank_code": "BCA"
}The payment service takes care of routing the request to the right provider (e.g., a bank for credit cards or GoPay for wallets). From the caller’s perspective, it’s simple: they hit one endpoint, pass in the payment details, and get a response. They don’t need to know the nitty-gritty of how each method is implemented.
Why One Endpoint Works Here
- Unified Experience
For clients integrating with your payment service (say, a website or app), a single endpoint is way easier to use than separate ones like /payments/credit-card, /payments/internet-banking, etc. It’s one URL, one set of docs, and one integration to worry about. - Shared Domain Logic
Even though the implementation details vary, payments share common logic—like validating amounts, checking for fraud, or logging transactions. A single endpoint lets you centralize this logic, reducing duplication. - Flexibility
If you add a new payment method (say, cryptocurrency), you don’t need to create a new endpoint. Just update the type options and handle the new logic internally. Clients don’t have to change their integration. - Real-World Precedent
If you look at popular payment gateways like Stripe or PayPal, they often use a single endpoint for creating payments (e.g., /v1/charges in Stripe). The method—credit card, Apple Pay, etc.—is specified in the request. This approach is battle-tested and developer-friendly.
So, when you’re dealing with features that fall under the same domain, a single API can simplify things without sacrificing clarity.
How to Decide: A Checklist
By now, you’re probably starting to see the pattern. But to make it super practical, here’s a checklist to help you decide whether to go with one API or multiple:
- Is it the same domain?
If the features you’re building share the same business context (like payments or user profiles), lean toward a single endpoint. If they’re distinct domains (like hotel bookings vs. product sales), separate endpoints are usually better. - How complex is the logic?
Combining features into one endpoint can work if the logic stays manageable. But if you’re writing tons of if-else statements to handle different cases, it’s a sign you might need to split things up. - Who owns it?
If different teams are responsible for the features, separate endpoints align better with team autonomy. A shared endpoint can create bottlenecks and coordination headaches. - How will clients use it?
Think about the developers calling your API. Will a single endpoint make their lives easier, or will it feel vague and overloaded? Clear, specific endpoints are often more intuitive. - What’s the scaling story?
If one feature is likely to see way more traffic than the others, separate endpoints let you scale them independently. A shared endpoint could become a bottleneck. - What’s your company’s setup?
Every organization divides domains differently. In some companies, hotel bookings and flight tickets might be one domain (e.g., “travel”). In others, they’re separate. Check how your company defines its boundaries before deciding.
A Real-World Example from the Trenches
To drive this home, let me share a story from my own experience. I once worked on a payment gateway (let’s call it GT Payment). Our job was to handle all sorts of payments—credit cards, bank transfers, internet banking, and digital wallets. At first, some folks on the team thought we should create separate endpoints for each method: /credit-card, /bank-transfer, etc. It seemed logical because each method was so different.
But after digging into it, we realized they all belonged to the payment domain. The core job was the same: take money from a customer and send it to a merchant. So, we went with a single endpoint: POST /payments. The request body had a type field to specify the method, and the backend handled the routing to the right provider.
This was a game-changer. For our clients (e-commerce sites, mostly), integrating was dead simple—they just called one endpoint and passed in the details. We could add new payment methods without forcing them to update their code. Internally, the codebase was clean because we centralized the shared logic (like fraud checks) and only branched out for method-specific stuff.
Contrast that with another project I saw, where a company tried to use one endpoint for everything—hotel bookings, car rentals, and event tickets. It was a mess. The endpoint had to handle so many cases that the code was riddled with conditionals, and every change risked breaking something unrelated. Eventually, they split it into separate endpoints per domain, and life got way easier.
Another Tips
Sometimes, the line between “same domain” and “different domains” isn’t crystal clear. For example, what if you’re building a travel platform that handles hotels, flights, and car rentals? Are those one domain (“travel”) or three separate ones? It depends on your company.
In some organizations, anything travel-related is treated as a single domain, so you might have one microservice (and one set of APIs) for all of it. In others, hotels and flights are split because they involve different partners, data models, and teams. If you’re not sure, talk to your team or stakeholders to understand how they define the boundaries. There’s no universal rule—context is everything.
Another tricky case is when you start with one domain but it grows. Say you build a payment service with a single endpoint, and it works great. Then you add subscriptions, refunds, and payouts. Suddenly, your “payment domain” feels like it’s splitting into sub-domains. At that point, you might need to rethink your APIs and split them up to keep things manageable.
Best Practices for API Design
Whether you go with one endpoint or many, here are some tips to make your APIs shine:
- Keep It Consistent
If you use separate endpoints, follow a consistent naming pattern (e.g., /service-name/resource/action). If you use one endpoint, make sure the request format is predictable across types. - Document Everything
Clear docs are a lifesaver. For a single endpoint, explain how the type field works and what fields are required for each type. For multiple endpoints, document each one’s purpose and payload. - Version Your APIs
Things change. Versioning (e.g., /v1/payments) lets you update your APIs without breaking existing clients. - Handle Errors Gracefully
Whether it’s one endpoint or many, return clear error messages. If a refund fails because of a hotel policy, say so—don’t just throw a generic “400 Bad Request.” - Test for Scale
Simulate heavy traffic to make sure your endpoint(s) can handle the load, especially if you’re combining multiple services into one.
Wrapping Up
Deciding whether to create one API for multiple services or separate APIs for each comes down to understanding your domains. If you’re working within the same domain—like different payment methods—a single endpoint can simplify things for everyone. But if you’re crossing domains—like hotel bookings and product sales—separate endpoints keep your code clean, your teams independent, and your services scalable.
There’s no perfect formula, and every company draws its domain lines differently. The key is to think about the logic, the teams, and the clients using your APIs. Use the checklist I shared, talk to your team, and you’ll land on the right approach.
So, next time you’re staring at your API design and wondering, One or many?, take a step back, map out your domains, and let the context guide you. You’ve got this!
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