context: caching reverse proxy with balancer setup (but only one worker yet) All content delivered from the backend without Last-Modified header is only cached until the expiry-date is reached once although there is an future Expires header. No re-caching appears. CacheIgnoreNoLastMod does not affect this behaviour. According to the docs (and -as far as I understand- RFC2616) an Expires-Header alone should be sufficient. Moreover CacheIgnoreNoLastMod should make caching possible even when Last-Modified header is missing. Sounds similiar to 27791, but forcing Last-Modified to be set on the backend makes the Problem disappear. Headers from backend triggering the problem: --- HTTP/1.1 200 OK Date: Wed, 10 Jun 2009 12:27:14 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch11 mod_ssl/2.2.3 OpenSSL/0.9.8c X-Powered-By: PHP/5.2.0-8+etch11 Cache-Control: max-age=300 Expires: Wed, 10 Jun 2009 12:32:14 GMT Connection: close Content-Type: text/html;charset=utf-8 --- after 300sec from the first access the proxy-cache keeps ignoring the cache: --- HTTP/1.1 200 OK Date: Wed, 10 Jun 2009 12:31:06 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch11 mod_ssl/2.2.3 OpenSSL/0.9.8c X-Powered-By: PHP/5.2.0-8+etch11 Cache-Control: max-age=300 Expires: Wed, 10 Jun 2009 12:36:06 GMT Content-Type: text/html;charset=utf-8 Via: 1.0 www.taz.de Connection: close --- when Last-Modified id forced on backend like: --- HTTP/1.1 200 OK Date: Wed, 10 Jun 2009 12:34:33 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch11 mod_ssl/2.2.3 OpenSSL/0.9.8c X-Powered-By: PHP/5.2.0-8+etch11 Last-Modified: Wed, 10 Jun 2009 12:34:33 GMT Expires: Wed, 10 Jun 2009 12:39:33 GMT Cache-Control: max-age=300 Connection: close Content-Type: text/html;charset=utf-8 ... the proxy-cache behaves: --- HTTP/1.1 200 OK Date: Wed, 10 Jun 2009 12:36:48 GMT Server: Apache/2.2.3 (Debian) Last-Modified: Wed, 10 Jun 2009 12:36:34 GMT X-Powered-By: PHP/5.2.0-8+etch11 Cache-Control: max-age=300 Expires: Wed, 10 Jun 2009 12:41:34 GMT Via: 1.1 www.taz.de Age: 14 Content-Length: 89601 Keep-Alive: timeout=15, max=300 Connection: Keep-Alive Content-Type: text/html;charset=utf-8 --- relevant config on proxy cache machine: --- ProxyPreserveHost On ProxyPass / balancer://webcluster/ <Proxy balancer://webcluster> ... </Proxy> CacheEnable mem / --- on backend --- ExpiresActive On ExpiresByType text/html "access plus 5 minutes" --- The following line in my PHP app cures the desease: --- header( "Last-Modified: ". gmdate( "D, d M Y H:i:s", time() ) ." GMT"); --- regards, Filip Moritz
Please check if this also happens with the disk cache. The mem cache has a worse performance than the disk cache and various other drawbacks.
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