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11 min readPublished Oct 16, 2023

What is a realtime API? Different types and when to use them

Realtime data worldwide continues to grow exponentially every minute as more people, devices, websites, IoT sensors, and other technologies find ways to stay connected on the internet. By 2025, more than 25% of all data created is expected to be realtime, and 95% will come from the Internet of Things, according to IDC Data Age.

As such, users have become heavily reliant on realtime applications in their daily activities, including streaming entertainment and sports, ride-share applications, banking transactions, social networks, stock trading, and online gaming. Applications like Uber, TradingView, YouTube, and Facebook leverage Realtime APIs to provide their users with accurate, relevant, and timely information in microseconds.

In this article, we'll take a closer look at realtime APIs and their significance, workings, and practical applications. We'll also discuss the technologies that drive them and how you can use realtime communication to enhance your software solutions. 

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What is a realtime API?

Realtime APIs are interfaces that allow continuous data flow between applications without the need for repeated requests, with an industry-standard response time of less than 30ms. Unlike the traditional HTTP request API, where an application sends a request and waits for a response, realtime APIs allow for bidirectional, long-lasting communication between client and server. This means clients can receive data as soon as it is available, providing live updates and a seamless and interactive user experience.

Realtime APIs have revolutionized how we interact with modern applications –  enabling us to build applications that help users connect with friends, deliver changes in stock prices in a fraction of a second, and collaborate with team members worldwide.

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How do realtime APIs work?

Realtime APIs leverage several technologies and protocols to deliver data with low latency and provide realtime experiences. The two major underlying technologies used in building realtime APIs are WebSocket and SSE(Server-Sent Events).

WebSocket is a communication protocol that facilitates two-way and full-duplex communication between clients and servers over a long-lived and persistent connection. 

Once the client and server are connected, they remain connected as long as possible. They can send data to one another, making it easy to deliver data in realtime and build interactive applications. This eliminates the overhead of establishing new connections for each request, reducing latency and enabling realtime updates to flow continuously.

A WebSocket connection starts with a handshake where the client sends an HTTP request to the server with the intent of upgrading the request to the WebSocket protocol later. Once the request is received and validated, the server upgrades and switches the connection from the HTTP protocol to the WebSocket protocol, allowing for long-lasting and two-way communication. The WebSocket protocol provides full-duplex communication, making it possible for the server and client to send data independently and simultaneously.

WebSocket follows an event-driven architecture. Events, such as messages or notifications, trigger data transmission. When an event occurs, the server pushes relevant data to the connected clients, ensuring realtime updates.

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SSE (Server-Sent Events)

Some applications like online gaming and messaging apps might benefit from bidirectional communication for realtime data transmission. News streaming and stock trading applications, however, are well suited for unidirectional communication where the servers send realtime updates to the clients. These kinds of applications leverage protocols like SSE to facilitate long-lasting unidirectional communications from the server to the client.

SSE is based on standard HTTP connections, making it easy and efficient to implement in applications. Clients establish an HTTP connection to the server and keep it open, awaiting server-sent updates.

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Types of realtime API

There are different types of realtime API, suited to different use cases. Let's look at five of the most popular.

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Streaming APIs

Streaming APIs or Firehose APIs are a family of realtime APIs that make it possible for a server to send data streams to multiple clients and vice-versa, ensuring that data is delivered immediately when it’s available. Their ability to maintain persistent connections and push data in realtime has transformed industries ranging from entertainment and finance to IoT and social networking. 

Streaming APIs are crucial when building applications where instant updates and live streams are a priority to deliver live video broadcasts to users. Video live streaming apps like Twitch, YouTube Live, and social networking platforms like Twitter and Facebook use Streaming APIs to update users' timelines with realtime posts and updates. 

A streaming API typically handles message ordering, stream continuity/resumption, and contiguous serial numbers to maintain data integrity. Message ordering ensures that messages are delivered in the same sequence they were published. Stream continuity or resumption allows for automatic reconnection and resuming from the point of disconnection within a certain time frame. Contiguous serial numbers involve a straightforward series of `ACK` (Acknowledgment) or `NACK` (Negative Acknowledgment) responses, addressing each contiguous sequence of messages. Kafka provides a streaming API that adheres to this model for internal systems.

Pub/Sub, short for "Publish/Subscribe," is a messaging software design pattern that allows asynchronous communication between different components or systems. In a Pub/Sub system, publishers (producers) are responsible for broadcasting messages to specific channels or topics, while subscribers (consumers) express their interest by subscribing to these channels.

In modern application architectures, applications are broken down into smaller, independent building blocks known as services. Pub/Sub messaging enables instant event notifications for these distributed systems, providing scalable and reliable communication between independent software modules. 

News websites and applications use Pub/Sub APIs to deliver breaking news updates to subscribers in realtime.

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Pub/Sub models

Pub/Sub systems can be categorized into two basic models based on flow of data and the publisher-to-subscriber relationships.

  • One-to-many (broadcast): In this model, a single publisher broadcasts messages to multiple subscribers interested in a particular topic. It's suitable for services like news updates or notifications.

  • Many-to-many (group messaging): This model allows multiple participants to exchange messages within a group or channel. It's commonly used in chat applications and collaborative tools where multiple users need to communicate in a shared space.

Although Pub/Sub has been around for over 30 years, its design does not define any semantics around ordering or continuity when there is a loss of connection. Despite being a widely used pattern today, it’s important to consider and address these issues in our world of unreliable connections.

Fortunately, solutions like Ably offer a Pub/Sub API that follows the same model but with added guarantees around ordering, continuity, idempotency, and more.

Push APIs, also referred to as push notification APIs, are interfaces that enable servers to send realtime updates, messages, or notifications to clients (including mobile devices and web browsers) without the need for the client to initiate a request. They allow for the efficient and timely "pushing" of data from servers to clients. 

Push APIs are crucial in delivering time-sensitive information, updates, or alerts directly to users' devices. They provide a means for applications to engage users with relevant and timely content, thereby enhancing the user experience.

Push notifications are a common method for sending messages, news updates, weather alerts, and other information to mobile devices when a user is not actively using an application or website. Unsurprisingly, Push APIs are used extensively for this purpose. For instance, e-commerce platforms use push notifications to notify users about special offers, order updates, and product availability, which can lead to increased sales.

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Event-driven APIs

Realtime communication is made possible through event-driven APIs, which are based on the principles of event-driven architecture. This architecture focuses on the production, consumption, and processing of events, with components mainly communicating by generating and responding to events.

Event-driven APIs allow for the transmission of events between clients and servers, resulting in immediate updates and interactions. The APIs are designed around events that represent changes or occurrences within a system. 

Events within the system can be activated by user actions like clicking a button, submitting a form, or interacting with a user interface element. For instance, when a user sends a message in a chat application, a "message sent" event is triggered. The system itself can generate events based on its internal state or operations. For example, when a server changes its status from "online" to "offline," it can trigger a "server status change" event. Events can also originate from external data sources or devices, such as sensor readings in an IoT system like temperature changes or motion detection.

When an event is triggered within the system, it is processed on the server. Event processing involves validation, data transformation, and determining which clients should receive the event. Once processed, the server distributes the event to the relevant clients in realtime, ensuring that all connected clients are promptly informed of the event. Clients can then react to the event accordingly.

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What are the benefits of realtime APIs?

  1. Reduced latency: Realtime APIs create persistent connections between clients and servers, allowing instant data and update delivery. This significantly reduces latency and is useful in applications such as live chat, online gaming, financial trading, and collaborative tools that require low latency for realtime decision-making and user satisfaction.

  2. Realtime data synchronization: Realtime APIs facilitate effortless data synchronization among multiple users or devices, promoting easy collaboration while ensuring data consistency.

  3. Improved efficiency: Realtime APIs provide instant task/system status updates, helping organizations identify bottlenecks and increase productivity.

  4. Interactive user experience: Realtime APIs provide users with immediate feedback and realtime information, resulting in a more interactive user experience, higher user satisfaction, and increased engagement.

  5. Better Scalability:  Realtime WebSocket APIs can handle multiple concurrent connections with minimal overhead, enabling efficient scaling compared to traditional request-response models.

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When to choose a realtime API

Realtime APIs are important for any application were the user experience is improved by data flowing from producers to consumers in the shortest amount of time possible.

Below are some of the most common use cases:

Messaging apps

Realtime APIs are essential to instant messaging applications like WhatsApp, Telegram, and Slack. These apps rely on realtime communication to instantly deliver messages to users through text, images, or files. Push APIs are used to send users notifications, ensuring they never miss an important message.

Social media feeds

Social media platforms like Twitter and Facebook use realtime APIs, allowing users to receive instant posts, comments, and notifications updates. This feature enables users to stay up-to-date with new content as it is published, ultimately fostering active engagement within their respective online communities.

Collaboration tools

Realtime APIs available in Microsoft Teams and Google Workspace facilitate easy collaboration by providing features like collaborative editing, live chat messages, and realtime video conferencing. Collaborative work on the same document saves time and avoids confusion, making teams more efficient regardless of location.

Online gaming

Online gaming platforms like Steam, Xbox Live, and PlayStation Network use realtime APIs for interactive multiplayer gameplay. With the help of these APIs, players can engage in interactive, competitive, and communicative experiences with one another in realtime.

Live streaming

Streaming services like Twitch, YouTube Live, and Netflix use realtime APIs to deliver live video and content to users. Viewers can watch events as they happen, providing an interactive experience.

Financial Markets

Stock trading platforms like Bloomberg Terminal and E*TRADE rely on realtime APIs to provide up-to-the-second financial data for traders and investors. Realtime updates are essential for making informed decisions in rapidly changing markets.

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Deliver realtime experiences at scale with Ably

Realtime technology isn't just a luxury anymore — it's a must-have for any app that wants to deliver the seamless experiences that users crave. 

Ably offers a reliable, scalable, and feature-rich platform that caters to both new and established projects. Our Pub/Sub APIs are designed for a variety of realtime applications, including collaborative experiences, live chat, data broadcast, and notifications.

Explore our documentation and see how easy it is to integrate realtime features into your apps. Or sign up for a free account and start building today.

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Realtime API FAQs

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What is a realtime messaging API?

A realtime messaging API is a type of API that facilitates instant messaging and communication between clients. It allows users or applications to send and receive messages in realtime, making it suitable for chat applications, notifications, and collaborative tools.

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Can a REST API be realtime?

Conventional REST APIs do not have realtime capabilities. They use a request-response model, where the client sends a request to the server, and the server sends back data. In contrast, realtime APIs offer immediate updates without the need for multiple requests.

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How do I get realtime data from an API?

To receive realtime data from an API, it's important to use an API that supports realtime communication. This can be achieved through WebSocket-based APIs, server-sent events (SSE), or long polling. By connecting to the API, you can receive updates as they happen.

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How to use a realtime API?

To use a realtime API, you need to connect your application to the API server.The API will send updates to your application immediately whenever there are new data or messages on the server. 

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Are all APIs realtime? 

No, not all APIs are realtime. Traditional RESTful APIs follow a request-response model and do not provide realtime updates. Realtime APIs are specifically designed to deliver data or messages instantly, often using technologies like WebSockets or server-sent events.

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