HTTP headers are key-value pairs sent in HTTP requests and responses, providing essential information about the communication between the client and server. They include details such as content type, encoding, cache control, authentication, and more, helping manage the behavior of HTTP transactions.

HTTP header optimization refers to customized optimization of HTTP headers during the CDN acceleration process, based on the needs of the enterprise. This includes ignoring forced refreshes, setting header size limits, and modifying, adding, or deleting headers.

Key Optimization Features and Implementation

Ignore Forced Refresh Feature

The challenge of handling forced refresh requests can significantly impact origin server performance and bandwidth consumption. The “Ignore Forced Refresh” feature in CDNetworks HTTP header optimization ensures that when a client (typically a browser) initiates a forced refresh request for cached content, the requested content is still served from the cache at the edge node. This avoids the need to revalidate the request with the origin server or to fetch the entire requested content from the origin before responding to the client.

Implementation Details
A forced refresh request refers to a special request initiated by the client (typically a browser) with the purpose of bypassing the cache and directly retrieving the latest content from the origin server. Such requests usually do not include the If-Modified-Since or If-None-Match headers, but they do contain the Pragma: no-cache or Cache-Control: max-age=0 request headers. Users typically initiate this type of request in their browser by pressing Ctrl+F5.

The “Ignore Forced Refresh” feature in CDNetworks’ HTTP header optimization allows the system to disregard forced refresh requests from browsers. When such requests are made, the content can still be delivered directly from the CDNetworks cache nodes. This functionality significantly reduces the processing load associated with validation requests at the origin server, as it mitigates the need for the server to respond to repeated requests for the same file, thereby conserving bandwidth and enhancing overall efficiency in content delivery.

This feature is especially applicable to websites that experience high load pressure at the origin server and require CDN acceleration, such as high-traffic e-commerce platforms and news portals.

HTTP Header Size Limitation

HTTP header size limitation refers to the ability of CDN nodes to impose limits on the size of request or response headers for user access after a website implements CDN acceleration. This security feature helps prevent potential attacks while ensuring stable service delivery.

Technical Implementation
The HTTP protocol uses a request/response model. The client sends a request to the server, where the request headers include:

• Request method
• URI
• Protocol version
• MIME-like message structure containing request modifiers, client information, and content
• The server responds with a status line, which includes the version of the message protocol, a success or error code, and accompanying information such as server details and entity metadata.

After configuring the HTTP header size limitation:

• If request headers exceed the configured maximum value, a “Bad Request” response is returned with a status code of 400
• If response headers exceed the configured maximum value, a “HTTP_HEADER_TOO_LARGE” response is returned with a status code of 601
  
  

Header Modification Capabilities

Some enterprises have specific business needs that require customized HTTP headers. However, directly customizing HTTP headers at the origin server may affect CDN acceleration, leading to:

• Lower cache hit rates
• Frequent user requests to the origin
• Increased load and bandwidth costs
• Degraded user experience

The header modification functionality allows users to control HTTP headers at the CDN level without needing to modify the source code.

Request Flow and Modification Points

After using CDNetworks CDN acceleration, the requests and responses from end users go through the following four stages:

1. The user sends a request to the CDN
2. The CDN sends a request to the origin server
3. The origin server returns a response to the CDN
4. The CDN returns a response to the user

The header modification functionality allows for the addition, deletion, and modification of HTTP headers and header content at each of these stages. Users can:

• Add security policies (such as Content-Security-Policy)
• Set cookie attributes (such as Set-Cookie)
• Conduct A/B testing
• Remove redundant header information
• Optimize header sizes for improved page loading
  
  

Summary

HTTP headers are a core component of HTTP requests and responses, playing a vital role in conveying essential information critical to managing communication between clients and servers. Optimizing HTTP headers can greatly enhance the efficiency and security of content delivery in the CDN acceleration process.

CDNetworks provides a variety of CDN acceleration solutions with capabilities for HTTP header optimization. These solutions are designed to accelerate and secure content delivery, improve website performance, and meet the increasing demands of users. For detailed information about our CDN acceleration services, please explore our Web Performance and Media Delivery offerings.