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From pgajdos <pgaj...@suse.cz>
Subject often mod_proxy cache revalidates
Date Wed, 16 Jun 2021 11:01:59 GMT
Hi,

from 2.4.48 on, mod_proxy-cache example [1] begins to fail for me.
Unfortunately I can not manage to expose this issue outside
apache-rex framework sofar. With 2.4.46, I can not see this at all.

$ git clone https://github.com/pgajdos/apache-rex.git
$ cd apache-rex
$ ./run-rex mod_proxy-cache
[..]
[1] reverse proxy with cache
< X-Cache: MISS from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
1 misses, 0 revalidates and 9 hits
[2] forward proxy with cache
< X-Cache: MISS from test
< X-Cache: REVALIDATE from test
< X-Cache: REVALIDATE from test
< X-Cache: REVALIDATE from test
< X-Cache: REVALIDATE from test
< X-Cache: REVALIDATE from test
< X-Cache: REVALIDATE from test
< X-Cache: REVALIDATE from test
< X-Cache: REVALIDATE from test
< X-Cache: REVALIDATE from test
1 misses, 9 revalidates and 0 hits

Example FAILED (subexample #2):
[..]
$

Former behavior for 2.4.46:

[1] reverse proxy with cache
< X-Cache: MISS from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
1 misses, 0 revalidates and 9 hits
[2] forward proxy with cache
< X-Cache: MISS from test
< X-Cache: REVALIDATE from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
< X-Cache: HIT from test
1 misses, 1 revalidates and 8 hits

Roughly: the example config (/tmp/apache-rex/mod_proxy-cache/httpd.conf) looks like:

------------------------------8<------------------------------------
ServerName test
User abuild
Group abuild
Listen 60080
PidFile /tmp/apache-rex/mod_proxy-cache/pid
ErrorLog /tmp/apache-rex/mod_proxy-cache/error_log
LoadModule auth_basic_module /usr/lib64/apache2-prefork/mod_auth_basic.so
LoadModule dir_module /usr/lib64/apache2-prefork/mod_dir.so
LoadModule authz_host_module /usr/lib64/apache2-prefork/mod_authz_host.so
LoadModule proxy_module /usr/lib64/apache2-prefork/mod_proxy.so
LoadModule proxy_http_module /usr/lib64/apache2-prefork/mod_proxy_http.so
LoadModule cache_module /usr/lib64/apache2-prefork/mod_cache.so
LoadModule log_config_module /usr/lib64/apache2-prefork/mod_log_config.so
LoadModule authz_core_module /usr/lib64/apache2-prefork/mod_authz_core.so
LoadModule cache_socache_module /usr/lib64/apache2-prefork/mod_cache_socache.so
LoadModule socache_shmcb_module /usr/lib64/apache2-prefork/mod_socache_shmcb.so
DocumentRoot /tmp/apache-rex/mod_proxy-cache/htdocs
DirectoryIndex index.html

### example configuration

LogFormat "%s %{cache-status}e" cache_format

Listen 60081
<VirtualHost *:60081>
  ErrorLog "/tmp/apache-rex/mod_proxy-cache/error_log-backend"
  DocumentRoot "/tmp/apache-rex/mod_proxy-cache/htdocs-backend"
  <Directory "/tmp/apache-rex/mod_proxy-cache/htdocs-backend">
    Require local
  </Directory>
</VirtualHost>

Listen 60082
<VirtualHost *:60082>
  ErrorLog "/tmp/apache-rex/mod_proxy-cache/error_log-reverse-proxy"

  <Location "/app/">
    ProxyPass "http://localhost:60081/"
  </Location>

  CacheSocache shmcb
  CacheSocacheMaxSize 102400
  CacheEnable socache "/"

  CacheHeader on

  CustomLog "/tmp/apache-rex/mod_proxy-cache/reverse-proxy-uncached.log" cache_format env=cache-miss
  CustomLog "/tmp/apache-rex/mod_proxy-cache/reverse-proxy-cached.log" cache_format env=cache-hit
  CustomLog "/tmp/apache-rex/mod_proxy-cache/reverse-proxy-revalidated.log" cache_format env=cache-revalidate
</VirtualHost>

Listen 60083
<VirtualHost *:60083>
  ErrorLog "/tmp/apache-rex/mod_proxy-cache/error_log-forward-proxy"

  ProxyRequests On
  <Proxy "*">
    Require local
  </Proxy>

  CacheSocache shmcb
  CacheSocacheMaxSize 102400
  # http://httpd.apache.org/docs/current/mod/mod_cache.html#cacheenable
  CacheEnable socache http://localhost:60081/

  CacheHeader on

  CustomLog "/tmp/apache-rex/mod_proxy-cache/forward-proxy-uncached.log" cache_format env=cache-miss
  CustomLog "/tmp/apache-rex/mod_proxy-cache/forward-proxy-cached.log" cache_format env=cache-hit
  CustomLog "/tmp/apache-rex/mod_proxy-cache/forward-proxy-revalidated.log" cache_format env=cache-revalidate
</VirtualHost>
------------------------------>8------------------------------------

And the script runs 10 requests on the server:

for i in $(seq 1 10); do
  curl -s -v --proxy http://localhost:60083/ http://localhost:60081/ 2>&1 | grep 'X-Cache'
  sleep 0.1
done


And again, I cannot reproduce for example with httpd run with
fx. -f /tmp/apache-rex/mod_proxy-cache/httpd.conf and running requests
manually. I will try harder, I just want to know first whether this is
something known or whether I have something completely wrong in the
configuration.

Thanks for your attention,
Petr

[1] https://github.com/pgajdos/apache-rex/tree/master/mod_proxy-cache

-- 
Have a lot of fun!

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