# Value of "Expires" header differ for caching and content serving servers **URL:** \ **Category:** NGINX\ **Created:** [April 6, 2011, 12:47pm UTC](https://www.ruby-forum.com/t/value-of-expires-header-differ-for-caching-and-content-serving-servers/205430 "2011-04-06T12:47:51Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\ **Post date:** [April 6, 2011, 12:47pm UTC](https://www.ruby-forum.com/t/value-of-expires-header-differ-for-caching-and-content-serving-servers/205430/1 "2011-04-06T12:47:51Z")
I have a following servers structure: content.server contains an Apache instance, which processes one simple PHP script. On the same node Nginx is set as a caching proxy to that Apache. caching.server contains Nginx with proxy\_cache directive, with upstream set to content.server Php script generates an XML file, that has a lifetime of 30 minutes. This is achieved by setting headers in PHP code: “Cache-Control: max-age=1800”, “Date: now()” and “Expires: now()+1800seconds”. content.server serves the cached file correctly: > Date Wed, 06 Apr 2011 09:50:49 GMT > Cache-Control public, must-revalidate, max-age=1800 > Expires Wed, 06 Apr 2011 10:14:25 GMT > Etag 26ee7051c360ee28d2a5697fb2b97a03 But approximately half of the time caching.server serves the content where Date header is larger than Expires, and Expires is different from the one on content.server: > Date Wed, 06 Apr 2011 09:49:58 GMT > Cache-Control public, must-revalidate, max-age=1800 > Expires Wed, 06 Apr 2011 09:44:23 GMT > Etag 26ee7051c360ee28d2a5697fb2b97a03 My questions is: what can cause such behaviour, when caching nginx sets its own Expires header? Posted at Nginx Forum: > **[Value of "Expires" header differ for caching and content serving servers](https://forum.nginx.org/read.php?2,188725,188725#msg-188725)** > > I have a following servers structure: content.server contains an Apache instance, which processes one simple PHP script. On the same node Nginx is set as a caching proxy to that Apache. caching.server contains Nginx with proxy\_cache directive, with... ---
**Author:** ![i.s.ivanov2](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/c4cdca/32.png) [@i.s.ivanov2](https://www.ruby-forum.com/u/i.s.ivanov2)\ **Post date:** [April 6, 2011, 1:40pm UTC](https://www.ruby-forum.com/t/value-of-expires-header-differ-for-caching-and-content-serving-servers/205430/2 "2011-04-06T13:40:21Z")
And an additional question: why haven’t nginx requested a new file, when “Expires” header becomes bigger than current date? Can it be caused by proxy\_cache\_valid any 10m; directive? Posted at Nginx Forum: > **[Re: Value of "Expires" header differ for caching and content serving servers](https://forum.nginx.org/read.php?2,188725,188736#msg-188736)** > > I have a following servers structure: content.server contains an Apache instance, which processes one simple PHP script. On the same node Nginx is set as a caching proxy to that Apache. caching.server contains Nginx with proxy\_cache directive, with... ---
**Author:** ![i.s.ivanov2](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/c4cdca/32.png) [@i.s.ivanov2](https://www.ruby-forum.com/u/i.s.ivanov2)\ **Post date:** [April 7, 2011, 1:46pm UTC](https://www.ruby-forum.com/t/value-of-expires-header-differ-for-caching-and-content-serving-servers/205430/3 "2011-04-07T13:46:37Z")
I’ve captured the debug output of the outlined problem: Expires tag is less than the date of request processing, but there is no expiration message like “http file cache expired: 4 1302149578 1302149592” Debug output: 2011/04/07 18:42:15 [debug] 10373#0: \*6 epoll add event: fd:16 op:3 ev:80000005 2011/04/07 18:42:15 [debug] 10373#0: \*6 http script var: “request” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http script var: “?” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http script var: “param=value” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http cache key: “request” 2011/04/07 18:42:15 [debug] 10373#0: \*6 add cleanup: 0925FDD4 2011/04/07 18:42:15 [debug] 10373#0: \*6 http file cache exists: 0 e:1 2011/04/07 18:42:15 [debug] 10373#0: \*6 cache file: “/var/cache/a/22/ad1686833f0e0b0411e5bb582061822a” 2011/04/07 18:42:15 [debug] 10373#0: \*6 add cleanup: 0925FE1C 2011/04/07 18:42:15 [debug] 10373#0: \*6 http file cache fd: 21 2011/04/07 18:42:15 [debug] 10373#0: \*6 read: 21, 0925FE68, 361, 0 2011/04/07 18:42:15 [debug] 10373#0: \*6 http upstream cache: 0 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy status 200 “200 OK” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “Server: nginx” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “Date: Thu, 07 Apr 2011 11:16:40 GMT” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “Content-Type: text/xml” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “Connection: close” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “X-Powered-By: PHP/5.3.3-fpm.1” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “Cache-Control: public, must-revalidate, max-age=1800” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “Expires: Thu, 07 Apr 2011 11:25:35 GMT” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “ETag: 26ee7051c360ee28d2a5697fb2b97a03” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header: “Content-Length: 2102” 2011/04/07 18:42:15 [debug] 10373#0: \*6 http proxy header done 2011/04/07 18:42:15 [debug] 10373#0: \*6 http file cache send: /var/cache/a/22/ad1686833f0e0b0411e5bb582061822a 2011/04/07 18:42:15 [debug] 10373#0: \*6 posix\_memalign: 092300C0:4096 @16 2011/04/07 18:42:15 [debug] 10373#0: \*6 HTTP/1.1 200 OK Server: nginx/0.8.54 Date: Thu, 07 Apr 2011 11:42:15 GMT Content-Type: text/xml Connection: keep-alive X-Powered-By: PHP/5.3.3-fpm.1 Cache-Control: public, must-revalidate, max-age=1800 Expires: Thu, 07 Apr 2011 11:25:35 GMT ETag: 26ee7051c360ee28d2a5697fb2b97a03 Content-Length: 2102 Posted at Nginx Forum: > **[Re: Value of "Expires" header differ for caching and content serving servers](https://forum.nginx.org/read.php?2,188725,189076#msg-189076)** > > I have a following servers structure: content.server contains an Apache instance, which processes one simple PHP script. On the same node Nginx is set as a caching proxy to that Apache. caching.server contains Nginx with proxy\_cache directive, with... ---
**Author:** ![i.s.ivanov2](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/c4cdca/32.png) [@i.s.ivanov2](https://www.ruby-forum.com/u/i.s.ivanov2)\ **Post date:** [April 7, 2011, 9:55pm UTC](https://www.ruby-forum.com/t/value-of-expires-header-differ-for-caching-and-content-serving-servers/205430/4 "2011-04-07T21:55:15Z")
On Thu, Apr 7, 2011 at 7:15 AM, Maxim D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > This doesn’t actually correct: Cache-Control max-age and Expires disagree. > According to max-age, document should expire at 10:20:49, while > expires set to 10:14:25. > > Unless configured to ignore some headers (with > proxy\_ignore\_headers directive) nginx will use first relevant > header it sees to actually expire cached document, Cache-Control > max-age in this case. Really? That behavior would seem to be at odds with the HTTP 1.1 specification. From RFC 2616 section 14.9.3: “If a response includes both an Expires header and a max-age directive, the max-age directive overrides the Expires header, even if the Expires header is more restrictive” ## As almost all origin servers send both Expires and Cache-Control in their default configurations, with the Expires header coming first, wouldn’t nginx end up doing the wrong thing most of the time? RPM ---
**Author:** ![i.s.ivanov2](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/c4cdca/32.png) [@i.s.ivanov2](https://www.ruby-forum.com/u/i.s.ivanov2)\ **Post date:** [April 7, 2011, 2:16pm UTC](https://www.ruby-forum.com/t/value-of-expires-header-differ-for-caching-and-content-serving-servers/205430/5 "2011-04-07T14:16:17Z")
Hello! On Wed, Apr 06, 2011 at 06:47:10AM -0400, i.s.ivanov2 wrote: > content.server serves the cached file correctly: > > > Date Wed, 06 Apr 2011 09:50:49 GMT > > Cache-Control public, must-revalidate, max-age=1800 > > Expires Wed, 06 Apr 2011 10:14:25 GMT > > Etag 26ee7051c360ee28d2a5697fb2b97a03 This doesn’t actually correct: Cache-Control max-age and Expires disagree. According to max-age, document should expire at 10:20:49, while expires set to 10:14:25. Unless configured to ignore some headers (with proxy\_ignore\_headers directive) nginx will use first relevant header it sees to actually expire cached document, Cache-Control max-age in this case. > its own Expires header? > Value of Expires header is preserved from original request, while > Date is current date on the server. Since document isn’t expired > yet (see above), you see Expires in the past. Maxim D. ---
**Author:** ![i.s.ivanov2](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/c4cdca/32.png) [@i.s.ivanov2](https://www.ruby-forum.com/u/i.s.ivanov2)\ **Post date:** [April 8, 2011, 3:28am UTC](https://www.ruby-forum.com/t/value-of-expires-header-differ-for-caching-and-content-serving-servers/205430/6 "2011-04-08T03:28:01Z")
Hello! On Thu, Apr 07, 2011 at 02:54:32PM -0500, Ryan M. wrote: > > > set to content.server > > specification. From RFC 2616 section 14.9.3: > > “If a response includes both an Expires header and a max-age > directive, the max-age directive overrides the Expires header, even if > the Expires header is more restrictive” Yes, I’m aware of the fact that it’s not exactly correct per RFC2616. The excuse is that nginx is HTTP/1.0 client. 😉 > As almost all origin servers send both Expires and Cache-Control in > their default configurations, with the Expires header coming first, > wouldn’t nginx end up doing the wrong thing most of the time? I believe most servers either don’t sent Expires/Cache-Control at all, or they agree. If you do really care - workaround is to use proxy\_ignore\_headers. Maxim D. ---
**Author:** ![i.s.ivanov2](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/c4cdca/32.png) [@i.s.ivanov2](https://www.ruby-forum.com/u/i.s.ivanov2)\ **Post date:** [April 11, 2011, 7:37am UTC](https://www.ruby-forum.com/t/value-of-expires-header-differ-for-caching-and-content-serving-servers/205430/7 "2011-04-11T07:37:50Z")
I’ve removed sending max-age directive from php script, and that helped. Thanks a lot! Posted at Nginx Forum: > **[Re: Value of "Expires" header differ for caching and content serving servers](https://forum.nginx.org/read.php?2,188725,190037#msg-190037)** > > I have a following servers structure: content.server contains an Apache instance, which processes one simple PHP script. On the same node Nginx is set as a caching proxy to that Apache. caching.server contains Nginx with proxy\_cache directive, with...