Optimizing Browser Cache Strategy and Cache-Control Headers

Problem Description
Browser caching is a core technique for front-end performance optimization. It can reduce redundant resource requests and significantly improve page loading speed. This topic focuses on how to optimize caching strategies by configuring HTTP caching headers (such as Cache-Control), including cache types, cache duration control, and cache invalidation mechanisms.

Solution Process

1. Understanding Basic Cache Types

   • Strong Cache: The browser directly checks the local cache. If the cache is not expired, it uses the cached resource directly without sending a request to the server. Controlled by the Cache-Control or Expires headers.
   • Negotiation Cache (Conditional Requests): The browser sends a request to the server. The server checks if the resource has changed by validating resource identifiers (such as Last-Modified or ETag). If unchanged, it returns a 304 status code, and the browser uses the local cache.

2. Configuring Key Directives of Cache-Control

   • max-age=<seconds>: Maximum cache time for the resource (e.g., max-age=31536000 means caching for one year).
   • public: Allows proxy servers to cache the resource (suitable for static resources).
   • private: Only allows the user's browser to cache (suitable for user-private data).
   • no-cache: Requires validation with the server to check if the resource is updated (enables negotiation cache).
   • no-store: Prohibits any caching (used for sensitive data).

3. Designing Strategies for Different Resource Types

   • Static Resources (e.g., JS/CSS/Images): Set a long cache duration (e.g., one year) and implement cache invalidation via filename hashing (when the file changes, the URL changes, forcing the browser to download the new resource).

     Cache-Control: public, max-age=31536000
     

   • HTML Files: Use no-cache or a short max-age to ensure timely updates of page content.

     Cache-Control: no-cache  # or max-age=0
     

4. Enhancing Negotiation Cache with ETag or Last-Modified

   • The server includes an ETag (resource hash) or Last-Modified (last modification time) when returning the resource.
   • On subsequent requests, the browser sends If-None-Match (corresponding to ETag) or If-Modified-Since (corresponding to Last-Modified). The server validates these and decides whether to return 304 or the new resource.

5. Practical Example of Cache Strategy

   • Static Resource Server Configuration (Nginx example):

     location /static/ {
         expires 1y;          # Equivalent to Cache-Control: max-age=31536000
         add_header Cache-Control "public";
     }  
     location /index.html {
         expires 0;           # Disable strong caching
         add_header Cache-Control "no-cache";
     }
     

6. Avoiding Common Pitfalls in Cache Strategy

   • Setting long cache for dynamic resources by mistake: Differentiate content via URL parameters or version numbers.
   • Overlooking CDN caching: CDNs must adhere to the origin server's cache headers; ensure configuration consistency.

By following the above steps, you can systematically formulate a caching strategy to balance resource freshness and loading performance.