link: Real-Time Notification Architectures
HTTP Polling
Diagram
Overview
HTTP polling is a technique used to repeatedly request data from a server at regular intervals. It is often used in scenarios where real-time data updates are required, but other methods like WebSockets are not feasible. HTTP polling helps maintain updated information on the client side without requiring continuous open connections.
Polling Techniques
Polling Techniques
- Short Polling: The client makes requests to the server at fixed, frequent intervals. Each request is independent, and the server responds immediately with the available data.
- Long Polling: The client makes a request to the server and the server holds the request open until new data is available or a timeout occurs. This reduces the number of requests compared to short polling.
How Short Polling Works
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- Client Request: The client sends a request to the server at fixed intervals.
- Server Response: The server processes the request and responds immediately with the current state of the data.
- Repeat: The client waits for a predefined period before sending another request.
How Long Polling Works
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- Client Request: The client sends a request to the server and keeps the connection open.
- Server Waits: The server holds the request open until new data is available or a timeout occurs.
- Server Response: When new data is available, the server responds with the updated information.
- Repeat: The client immediately sends a new request after receiving the response, maintaining the connection.
Why Use Polling?
Polling is used in scenarios where real-time data updates are required, but the server or infrastructure does not support more advanced techniques like WebSockets or Server-Sent Events (SSE). It is also useful in situations where firewall restrictions or security policies prevent the use of persistent connections.
Pros/Cons
Pros
- Simplicity: Easy to implement with standard HTTP requests and responses.
- Compatibility: Works with most web servers and client libraries without requiring special configurations.
- Firewall Friendly: Uses standard HTTP methods that are typically allowed through firewalls and proxies.
- Predictable Load: Generates predictable server load due to fixed interval requests in short polling.
Cons
- Inefficiency: Can generate a high number of unnecessary requests, especially with short polling, leading to increased bandwidth usage.
- Latency: May introduce latency in data updates, especially with longer polling intervals.
- Resource Intensive: Can strain server resources due to the high frequency of requests, particularly in large-scale applications.
- Scalability Issues: Not ideal for applications with a large number of clients, as it can lead to server overload.
HTTP polling is a viable technique for achieving real-time data updates when more efficient methods are not available, but it comes with trade-offs in terms of efficiency and scalability. Choosing between short polling and long polling depends on the specific requirements and constraints of the application.