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From pgajdos <pgaj...@suse.cz>
Subject Re: often mod_proxy cache revalidates
Date Mon, 21 Jun 2021 13:06:38 GMT
Hi,

how to more easily reproduce: with following configuration file,
located e. g. in /tmp/apache-rex/mod_proxy-cache/httpd.conf:


On Wed, Jun 16, 2021 at 01:01:59PM +0200, pgajdos wrote:
> ------------------------------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------------------------------------

following script:

--------------------------------8<------------------------------------
mkdir -p /tmp/apache-rex/mod_proxy-cache/htdocs-backend
echo 'Backend for reverse' > /tmp/apache-rex/mod_proxy-cache/htdocs-backend/index.html

sleep 1

echo "[2] forward proxy with cache"
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
-------------------------------->8------------------------------------

gives:

$ sh run.sh
[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
$

Altering (or touching) the the index file is essential, as well as the
sleep afterwards.

Petr

--
Have a lot of fun!

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