Hi httpd users,
I've been testing Apache httpd 2.2.4 as a reverse-caching proxy server but
I've ran into some odd behavior with how its handling expired content.
Currently I'm using the worker MPM and mod_mem_cache to provide the storage.
I haven't tested this with prefork or mod_disk_cache yet, but if its worth it
I can test that configuration too. Here are some entries from the error log
with loglevel debug:
[Thu May 24 15:20:07 2007] [debug] mod_cache.c(129): Adding CACHE_SAVE filter
for /cgi-bin/showarticle/ca/259
[Thu May 24 15:20:07 2007] [debug] mod_cache.c(136): Adding CACHE_REMOVE_URL
filter for /cgi-bin/showarticle/ca/259
[Thu May 24 15:20:07 2007] [debug] mod_proxy_http.c(54): proxy: HTTP:
canonicalising URL //staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:20:07 2007] [debug] proxy_util.c(1378): [client 198.144.205.143]
proxy: http: found worker http://staging.greatschools.net/ for
http://staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:20:07 2007] [debug] mod_proxy.c(777): Running scheme http
handler (attempt 0)
[Thu May 24 15:20:07 2007] [debug] mod_proxy_http.c(1662): proxy: HTTP: serving
URL http://staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:20:07 2007] [debug] proxy_util.c(1798): proxy: HTTP: has
acquired connection for (staging.greatschools.net)
[Thu May 24 15:20:07 2007] [debug] proxy_util.c(1859): proxy: connecting
http://staging.greatschools.net/cgi-bin/showarticle/ca/259 to
staging.greatschools.net:80
[Thu May 24 15:20:07 2007] [debug] proxy_util.c(1955): proxy: connected
/cgi-bin/showarticle/ca/259 to staging.greatschools.net:80
[Thu May 24 15:20:07 2007] [debug] proxy_util.c(2050): proxy: HTTP: fam 2
socket created to connect to staging.greatschools.net
[Thu May 24 15:20:07 2007] [debug] proxy_util.c(2146): proxy: HTTP: connection
complete to 198.144.205.147:80 (staging.greatschools.net)
[Thu May 24 15:20:07 2007] [debug] mod_proxy_http.c(1448): proxy: start body
send
[Thu May 24 15:20:07 2007] [debug] mod_headers.c(663): headers:
ap_headers_output_filter()
[Thu May 24 15:20:07 2007] [debug] mod_cache.c(609): cache: Caching url:
/cgi-bin/showarticle/ca/259
[Thu May 24 15:20:07 2007] [debug] mod_cache.c(615): cache: Removing
CACHE_REMOVE_URL filter.
[Thu May 24 15:20:07 2007] [info] mem_cache: Cached url:
http://yahooed.nuked.greatschools.net:80/cgi-bin/showarticle/ca/259?
[Thu May 24 15:20:07 2007] [debug] mod_proxy_http.c(1537): proxy: end body send
[Thu May 24 15:20:07 2007] [debug] proxy_util.c(1816): proxy: HTTP: has
released connection for (staging.greatschools.net)
When the server is first started, and content is requested from a client, it
fetches the content from the backend server (staging.greatschools.net) and
stores it in memory cache from mod_mem_cache.
[Thu May 24 15:20:10 2007] [debug] mod_cache.c(263): cache: running CACHE_OUT
filter
[Thu May 24 15:20:10 2007] [debug] mod_cache.c(277): cache: serving
/cgi-bin/showarticle/ca/259
[Thu May 24 15:20:10 2007] [debug] mod_cache.c(263): cache: running CACHE_OUT
filter
[Thu May 24 15:20:10 2007] [debug] mod_cache.c(277): cache: serving
/cgi-bin/showarticle/ca/259
[Thu May 24 15:20:11 2007] [debug] mod_cache.c(263): cache: running CACHE_OUT
filter
[Thu May 24 15:20:11 2007] [debug] mod_cache.c(277): cache: serving
/cgi-bin/showarticle/ca/259
[Thu May 24 15:20:11 2007] [debug] mod_cache.c(263): cache: running CACHE_OUT
filter
[Thu May 24 15:20:11 2007] [debug] mod_cache.c(277): cache: serving
/cgi-bin/showarticle/ca/259
Further requests are serviced directly from the cache, which is what I want.
[Thu May 24 15:33:50 2007] [debug] cache_storage.c(272): Cached response for
/cgi-bin/showarticle/ca/259 isn't fresh. Adding/replacing conditional request
headers.
[Thu May 24 15:33:50 2007] [debug] mod_cache.c(129): Adding CACHE_SAVE filter
for /cgi-bin/showarticle/ca/259
[Thu May 24 15:33:50 2007] [debug] mod_cache.c(136): Adding CACHE_REMOVE_URL
filter for /cgi-bin/showarticle/ca/259
[Thu May 24 15:33:50 2007] [debug] mod_proxy_http.c(54): proxy: HTTP:
canonicalising URL //staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:33:50 2007] [debug] proxy_util.c(1378): [client 198.144.205.143]
proxy: http: found worker http://staging.greatschools.net/ for
http://staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:33:50 2007] [debug] mod_proxy.c(777): Running scheme http
handler (attempt 0)
[Thu May 24 15:33:50 2007] [debug] mod_proxy_http.c(1662): proxy: HTTP: serving
URL http://staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:33:50 2007] [debug] proxy_util.c(1798): proxy: HTTP: has
acquired connection for (staging.greatschools.net)
[Thu May 24 15:33:50 2007] [debug] proxy_util.c(1859): proxy: connecting
http://staging.greatschools.net/cgi-bin/showarticle/ca/259 to
staging.greatschools.net:80
[Thu May 24 15:33:50 2007] [debug] proxy_util.c(1955): proxy: connected
/cgi-bin/showarticle/ca/259 to staging.greatschools.net:80
[Thu May 24 15:33:50 2007] [debug] proxy_util.c(2050): proxy: HTTP: fam 2
socket created to connect to staging.greatschools.net
[Thu May 24 15:33:50 2007] [debug] proxy_util.c(2146): proxy: HTTP: connection
complete to 198.144.205.147:80 (staging.greatschools.net)
[Thu May 24 15:33:50 2007] [debug] mod_proxy_http.c(1448): proxy: start body
send
[Thu May 24 15:33:50 2007] [debug] mod_headers.c(663): headers:
ap_headers_output_filter()
[Thu May 24 15:33:50 2007] [debug] mod_proxy_http.c(1537): proxy: end body send
[Thu May 24 15:33:50 2007] [debug] proxy_util.c(1816): proxy: HTTP: has
released connection for (staging.greatschools.net)
The content, via the "Expires" header is set to expire in 10 minutes after the
request. Apache httpd correctly notes that the content is expired and
requests fresh content from the backend.
[Thu May 24 15:33:51 2007] [debug] cache_storage.c(272): Cached response for
/cgi-bin/showarticle/ca/259 isn't fresh. Adding/replacing conditional request
headers.
[Thu May 24 15:33:51 2007] [debug] mod_cache.c(129): Adding CACHE_SAVE filter
for /cgi-bin/showarticle/ca/259
[Thu May 24 15:33:51 2007] [debug] mod_cache.c(136): Adding CACHE_REMOVE_URL
filter for /cgi-bin/showarticle/ca/259
[Thu May 24 15:33:51 2007] [debug] mod_proxy_http.c(54): proxy: HTTP:
canonicalising URL //staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:33:51 2007] [debug] proxy_util.c(1378): [client 198.144.205.143]
proxy: http: found worker http://staging.greatschools.net/ for
http://staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:33:51 2007] [debug] mod_proxy.c(777): Running scheme http
handler (attempt 0)
[Thu May 24 15:33:51 2007] [debug] mod_proxy_http.c(1662): proxy: HTTP: serving
URL http://staging.greatschools.net/cgi-bin/showarticle/ca/259
[Thu May 24 15:33:51 2007] [debug] proxy_util.c(1798): proxy: HTTP: has
acquired connection for (staging.greatschools.net)
[Thu May 24 15:33:51 2007] [debug] proxy_util.c(1859): proxy: connecting
http://staging.greatschools.net/cgi-bin/showarticle/ca/259 to
staging.greatschools.net:80
[Thu May 24 15:33:51 2007] [debug] proxy_util.c(1955): proxy: connected
/cgi-bin/showarticle/ca/259 to staging.greatschools.net:80
[Thu May 24 15:33:51 2007] [debug] proxy_util.c(2050): proxy: HTTP: fam 2
socket created to connect to staging.greatschools.net
[Thu May 24 15:33:51 2007] [debug] proxy_util.c(2146): proxy: HTTP: connection
complete to 198.144.205.147:80 (staging.greatschools.net)
[Thu May 24 15:33:51 2007] [debug] mod_proxy_http.c(1448): proxy: start body
send
[Thu May 24 15:33:51 2007] [debug] mod_headers.c(663): headers:
ap_headers_output_filter()
[Thu May 24 15:33:51 2007] [debug] mod_proxy_http.c(1537): proxy: end body send
[Thu May 24 15:33:51 2007] [debug] proxy_util.c(1816): proxy: HTTP: has
released connection for (staging.greatschools.net)
Here's where things get interesting. It appears the refreshed content is
never re-stored in the storage. Every request after this point needs to
contact the backend server to refresh the content until the server is
restarted.
Here are the headers the script I'm trying to cache is outputting for
reference:
HTTP/1.x 200 OK
Date: Thu, 24 May 2007 23:22:50 GMT
Server: Apache/1.3.37 (Unix) mod_perl/1.29 mod_ssl/2.8.28 OpenSSL/0.9.7e-p1
mod_jk/1.2.21
Expires: Thu, 24 May 2007 23:32:50 GMT
Cache-Control: public
P3P: policyref="http://dev.greatschools.net/w3c/p3p.xml";, CP="ALL DSP COR CUR DEVi PSA IVAi IVDi CONi
OUR IND UNI", policyref="http://dev.greatschools.net/w3c/p3p.xml";, CP="ALL DSP COR CUR DEVi PSA
IVAi IVDi CONi OUR IND UNI"
Content-Type: text/html; charset=ISO-8859-1
Vary: Accept-Encoding,User-Agent
Content-Encoding: gzip
Content-Length: 22468
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Note that the Content-Encoding gzip is actually from Apache 2.2.4 not the
backend.
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