NGINX缓存代理配置后始终返回MISS的原因咨询

Let’s dive into why you’re consistently seeing X-Proxy-Cache: MISS and walk through fixes step by step:

1. Cache-Control Headers Might Be Bypassing the Cache #

Your configuration includes proxy_cache_bypass $http_cache_control;, which tells NGINX to skip the cache entirely if the client sends a Cache-Control header with directives like no-cache, no-store, or max-age=0 (common in refresh requests).

• Test this by forcing a cache-friendly request header:

  curl -I -H "Cache-Control: max-age=3600" https://example.com
  

  If this returns X-Proxy-Cache: HIT on the second request, your original requests were sending headers that bypassed the cache.
• You can also strip the Cache-Control header entirely to test:

  curl -I https://example.com -H "Cache-Control:"
  

2. Cache Directory Permissions Could Be Blocking Writes #

NGINX needs write access to the /tmp/nginx directory you specified for caching. If the user running NGINX (typically nginx or www-data) doesn’t have permissions here, it can’t store cache files at all.

• Check the directory permissions:

  ls -ld /tmp/nginx
  

• Fix permissions if needed (adjust the user/group to match your NGINX setup):

  chown -R nginx:nginx /tmp/nginx
  systemctl restart nginx
  

3. Backend Responses Might Be Preventing Caching #

Even if NGINX is configured to cache, it won’t store responses that include headers like Cache-Control: private, Cache-Control: no-cache, or Expires: 0.

• Inspect the raw response from your backend to check for these headers:

  curl -I http://127.0.0.1:8000
  

• If you want to override these backend headers, add proxy_ignore_headers Cache-Control Expires; to your location block to force NGINX to cache the response regardless.

4. Cache Key or Configuration Precedence Issues #

Your proxy_cache_key ("$scheme://$host$uri") only uses the protocol, host, and path—this is fine for static content without query parameters, but double-check:

• Are you accessing URLs with query parameters (e.g., ?id=123) that aren’t included in the cache key? While this would cause shared caching, it shouldn’t result in consistent MISS.
• Is there a more specific location block in your config that’s matching your requests instead of the one with caching enabled? NGINX uses the most specific location match first.

5. Test with a Minimal Cacheable Endpoint #

To rule out backend-specific issues, create a simple test location that returns static content:

location /test-cache {
    proxy_cache my_zone;
    proxy_cache_key "$scheme://$host$uri";
    proxy_cache_valid 200 10m;
    add_header X-Proxy-Cache $upstream_cache_status;
    return 200 "Test Cache Content";
}

Restart NGINX, then visit https://example.com/test-cache twice. If the second request returns X-Proxy-Cache: HIT, your core cache configuration works, and the problem lies with your backend’s response headers.

内容的提问来源于stack exchange，提问作者maxisme