In today‘s digitally connected world, APIs or Application Programming Interfaces power most of the apps and services we use every day. Let‘s first understand what exactly APIs are and why they are so ubiquitous and important for modern software applications.
What is an API?
At its core, an API is a set of definitions, protocols and tools for building software applications. An API specifies how two different components of software should interact and communicate with each other.
Let‘s break this down with an example. Imagine you are using a weather app on your phone. This weather app shows you daily forecasts and weather conditions for your current location. But where does this app get all the weather data from?
This is where APIs come in. The weather app uses an API exposed by a weather data provider. The app sends location information via API calls to the provider‘s servers, which send back formatted weather data for that place. The app then takes this data and displays it nicely in the app interface. Both systems interact via the standardized way laid out by the weather API.
Similarly, when you book a cab using Uber, your app communicates with Uber‘s servers for driver availability, fare estimates, ride status and so on via their API endpoints. APIs are everywhere – weather, maps, payment systems, banks, etc. Netflix uses APIs to stream movies, Facebook uses APIs to integrate with apps, Slack uses APIs for notifications.
According to Red Hat, 90% of all internet traffic today goes via APIs. So APIs truly power most of the digital services we use online and on our phones.
Why are APIs Important?
APIs allow different software systems to communicate and share data seamlessly. This has led to modular app development where frontends are separated from the backends. For example, the Netflix app‘s frontend focuses only on the user interface. The video catalog, streaming and other functions are handled via APIs on the backend. This brings many benefits:
- Abstract complexity – Frontend developers don‘t need to know or manage all backend complexities
- Faster development – Build quickly on existing APIs
- Reusability – APIs can be consumed across different platforms like web, mobile, IoT etc
- Decoupling – Frontend and backend can be developed independently
- Scalability – APIs help handle load better as systems scale
The API-first approach has become very popular where companies first design flexible APIs for their systems and then build applications on top of them. This strategic view makes APIs the core business enablers.
How Do APIs Work?
Now that we know what APIs are, let‘s look at how they actually work under the hood.
API Components
The main components that make up an API architecture are:
- Endpoint – The URI or URL where API requests are sent to
- Request – The API call made to the endpoint requesting data or an action
- Response – The data or confirmation returned by the API in response to the request
- Authentication – Keys or tokens used to validate API consumer identity
Let‘s use a simple example to understand how these components come together in an API call:
As you can see, the frontend app makes an HTTP request to the API endpoint with authentication credentials added to the headers. The API server validates these then runs business logic for the request. This could involve fetching data from a database or cache. The API response is then returned in a structured format like JSON or XML.
In this way, APIs enable straightforward integration between the consuming client app and the data/services exposed by the API provider.
Protocols and Formats
APIs use standard web protocols like HTTP and HTTPS for communication. Using open protocols makes APIs platform and language agnostic. The API payload data is serialized and returned in structured formats like:
- JSON (JavaScript Object Notation) – Simple and lightweight format that is easy to parse
- XML (Extensible Markup Language) – Self-descriptive format with more metadata
For real-time communication, WebSocket APIs are being used. GraphQL is gaining popularity as an alternative to REST APIs due to its flexibility and efficiency.
Documentation
Good documentation is crucial for any API since it helps developers understand how to use and integrate with it. OpenAPI Specification has emerged as a standard for defining REST API documentation in a source file. Auto-generated reference docs from this ensure documentation remains up-to-date as the API evolves.
API Architectural Styles
Over the years, different architectural paradigms have emerged for building APIs. Let‘s look at some major styles:
REST (Representational State Transfer)
REST or RESTful APIs have become the de facto standard for API design because of their simplicity, flexibility and scalability. REST uses HTTP requests to access API resources using CRUD operations:
- GET – Read resource
- POST – Create resource
- PUT – Update resource
- DELETE – Delete resource
Some examples of popular REST APIs are Twitter, Github, Stripe, Slack etc. However, REST has drawbacks like overfetching data, multiple API calls, and lack of structural documentation.
SOAP (Simple Object Access Protocol)
SOAP is a protocol that defines a standard XML-based messaging format for communication between APIs. SOAP APIs have built-in ACID compliance for reliability and security. However, SOAP is complex, heavyweight and lacks flexibility compared to REST.
RPC (Remote Procedure Call)
RPC enables triggering procedures and functions remotely via APIs. Popular RPC frameworks include JSON-RPC, XML-RPC, gRPC etc. RPC APIs are simple, versatile and useful for internal microservices.
GraphQL
GraphQL is a modern query language that gives clients more control and flexibility vs traditional REST APIs. Apps can specify exactly what data they need. This prevents both over and underfetching of data via multiple endpoints in REST. However, GraphQL requires apps to be designed specifically for this architecture.
Types of APIs
Based on who can access them, APIs are categorized as:
Public APIs
These APIs are open and available to any outside developer or app for integration. For example, Twilio, Stripe, WeatherAPI.com all offer public APIs. Public APIs usually require an API key or tokens for access.
Partner APIs
APIs provided by a company only to select business partners through collaborations and agreements. Shopify and Salesforce provide partner APIs to integrate with complementary services.
Private APIs
Private or internal APIs are meant only for use within an organization. These provide reusable logic, services and data access for internal developers and microservices.
Composite APIs
Composite APIs combine capabilities from multiple internal and external APIs into a single unified interface. This simplifies working with multiple APIs for developers.
API Security Considerations
While APIs provide controlled access to software capabilities and data, there are important security aspects to consider:
- Use HTTPS – Encrypt API traffic using SSL/TLS
- OAuth 2.0 – Industry standard for authentication and authorization
- API Keys – Unique identifiers to authenticate API clients
- Rate limiting – Prevent abuse or DDoS attacks
- Input validation – Sanitize any parameters passed to the API
- Access control – Grant API access to only authorized users and systems
Leading security standards like ISO 27001 should be followed for complete API security. Authentication, access policies, auditing, and monitoring are crucial.
API Use Cases
Let‘s look at some real-world API use cases:
Ecommerce
APIs enable custom ecommerce solutions by integrating payment, inventory, logistics, CRM and other systems. Shopify and Magento have APIs to build shopping experiences.
IoT and Devices
APIs allow IoT devices to connect and exchange data with backend services. Nest Thermostat uses APIs to sync temperature settings across devices.
Mobile Apps
Mobile apps for iOS and Android leverage APIs extensively for functions like maps, push notifications, social media, payments etc.
SaaS Integration
APIs enable SaaS apps like Gmail, Slack, HubSpot to integrate tightly with each other for unified workflows.
Mashups
Mashups combine capabilities from multiple external APIs to create new apps and digital experiences. Ex. Zapier integrates web apps via API mashups.
The API-Led Connectivity Revolution
APIs have clearly revolutionized software architecture, app development, and integration. As we enter an era of ubiquitous connectivity between systems, devices and apps, APIs will continue to power the interfaces and infrastructure enabling this integrated digital mesh.
Via cloud-based APIs, capabilities get effortlessly distributed across platforms. This API economy fosters innovation as developers combine APIs in novel ways. API management will be a key organizational discipline since APIs now drive business models and represent revenue channels.
In summary, investing in well-designed APIs and API-led strategies is key to succeeding in the digital-first world of the future.
