https://issues.apache.org/bugzilla/show_bug.cgi?id=47346
Summary: mod_cache doesn't re-cache expired content when
Last-Modified not set
Product: Apache httpd-2
Version: 2.2.3
Platform: PC
OS/Version: Linux
Status: NEW
Severity: major
Priority: P2
Component: mod_cache
AssignedTo: [email protected]
ReportedBy: [email protected]
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
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