HTTP Push Mechanism

Source: Dev.to

The Traditional HTTP Pull Model

By default, web communication follows the HTTP Pull model:

• The client sends a request
• The server processes it
• The server returns a response
• The connection is closed

Each request has a Time To Live (TTL), typically between 30 and 60 seconds, depending on the browser and environment.

If the server does not respond within this time window, the browser assumes the request has stalled and closes the connection. The client must then send a new request to try again.

This behavior is intentional. Open connections consume server resources such as memory and file descriptors, and servers can only handle a limited number of simultaneous connections. Without a timeout mechanism, a server could eventually exhaust its resources.

When HTTP Pull Is Not Enough

The HTTP Pull model works well for most use cases, but it breaks down in scenarios where:

• The server response takes longer than the TTL
• The server needs to send data as soon as it becomes available
• Low‑latency, real‑time updates are required

In these cases, repeatedly polling the server is inefficient and introduces unnecessary delays.

Persistent Connections and HTTP Push

To solve this, we use persistent connections.

A persistent connection remains open between the client and the server instead of closing after a single request‑response cycle. Once established, the server can push data to the client whenever it is ready, without waiting for a new request.

This communication pattern is commonly referred to as HTTP Push and forms the foundation of many real‑time web systems.

Keeping the Connection Alive: Heartbeat Interceptors

Browsers are designed to close idle connections. To prevent this from happening, persistent connections rely on heartbeat mechanisms.

Heartbeats are small, lightweight messages exchanged periodically between the client and the server. They usually contain no meaningful data. Their sole purpose is to signal that the connection is still active and should not be terminated due to inactivity.

Without heartbeats, browsers or proxies would close long‑lived connections, making HTTP Push unreliable.

The Cost of Persistent Connections

While powerful, persistent connections come with trade‑offs.

Compared to traditional HTTP Pull:

• They consume more memory per client
• They require more careful connection management
• They increase server complexity

Because each client holds an open connection, scalability becomes a critical concern. This is why HTTP Push should be used only when real‑time communication is truly required.

Real‑World Use Case: Multiplayer Browser Games

A clear example where HTTP Push is essential is browser‑based multiplayer games.

Players need to receive continuous, real‑time updates about game state, actions, and events. Polling the server every few seconds would result in poor responsiveness and a degraded user experience.

In this scenario, maintaining a persistent connection dramatically improves performance and responsiveness.

Common Technologies for HTTP Push

Several technologies are commonly used to implement long‑lived connections:

• Ajax Long Polling – Simulates push by keeping requests open until data is available
• WebSockets – Provides full‑duplex, real‑time communication over a single persistent connection
• Server‑Sent Events (SSE) – Allows servers to push one‑way updates to clients over HTTP

Each approach has its own strengths and trade‑offs, and the right choice depends on the application’s requirements.

Conclusion

HTTP Push enables real‑time communication by keeping connections open and allowing servers to send data as soon as it’s available. While this approach is more resource‑intensive than traditional HTTP Pull, it is indispensable for modern applications that demand low latency and real‑time updates.

Understanding how TTL, persistent connections, and heartbeat mechanisms work together helps engineers design systems that are both responsive and scalable. When used thoughtfully, HTTP Push can significantly enhance the user experience in modern web applications.