Caching with Apache mod_proxy

In case of complex inquiries or high volume of requests an external caching improves the answer time behaviour of the server.
For this the Apache provides a special module mod_proxy that is already pre-installed on 1und1-servers and is to be activated only.
Likewise the installation of the components may but need not happen on the same server. For the configuration the following entries are needed:

Apache 1.3

<IfModule mod_proxy.c>
    ProxyRequests Off
    ProxyVia On
    CacheRoot "/var/cache/httpd"
    CacheSize 100000 
    CacheGcInterval 4
    CacheMaxExpire 10
    CacheLastModifiedFactor 0.1
    CacheDefaultExpire 8
   # NoCache  domain1 domain2  
</IfModule>

The configuration of the VirtualHost is done in the http.conf. With confixx-Professional administered systems it is removed in the file confixx_vhost.conf. Maintenance is managed via the confixx-Professional web interface. It makes sense to apply for each web presentation an own client with dedicated domain(s).

<VirtualHost 217.160.211.236:80>
   ServerName web4.p15135474.pureserver.info
   ServerAlias  www.meinedomain.de.de roc-berlin.de
   DocumentRoot /home/www/web4/html
   User web4
   Group ftponly
   ScriptAlias /cgi-bin/ /home/www/web4/html/cgi-bin/
   php_admin_value open_basedir /home/www/web4/
   php_admin_value upload_tmp_dir /home/www/web4/phptmp/

   #RewriteEngine On
   #RewriteRule [s. ZMS Howto 'Apache rewrite']

</VirtualHost>

Note: The reboot of Apache is best done with: rcapache restart resp. stop|start, because then the bootscript with all parameters is used.

Apache 2.0

# /etc/apache2/mods-enabled/proxy.conf #

<IfModule mod_proxy.c>
  ProxyRequests Off
  <Proxy *>
     AddDefaultCharset off
     Order deny,allow
     Deny from all
     ProxyFtpDirCharset UTF-8
   </Proxy>
  ProxyVia On
</IfModule>

# /etc/apache2/mods-enabled/disk_cache.conf #

<IfModule mod_disk_cache.c>
  CacheRoot /var/cache/apache2/mod_disk_cache
  CacheDirLevels 5
  CacheDirLength 3
</IfModule>

# /etc/apache2/sites-enabled/httpd-mySite.conf #

<Proxy *>
  Order allow,deny
  Allow from all
</Proxy>

<VirtualHost *>
  ServerName      www.hermann-husen.de

  RewriteEngine   On
  RewriteRule     ...

  CacheEnable          disk /
  CacheRoot            /path-to-MySite/proxycache
  CacheDirLevels       2
  CacheDirLength       1
  CacheIgnoreNoLastMod On
  CacheDefaultExpire   3600
</VirtualHost>

ZMS templates

The modifcation of ZMS templates is minimal. It must be made sure only that pages contain the needed information for caching in the header. This can be achieved by entry of the following DTML methods:

<dtml-if "REQUEST.get('preview','')=='preview' or (getObjProperty('attr_cacheable', REQUEST)==0)"
   ><dtml-call "RESPONSE.setHeader('Expires', '-1')"
   ><dtml-call "RESPONSE.setHeader('Cache-Control', 'no-cache')"
   ><dtml-call "RESPONSE.setHeader('Pragma', 'no-cache')"
><dtml-else><dtml-call "RESPONSE.setHeader('Expires', _.DateTime(_.DateTime().timeTime() +  86400).toZone('GMT').rfc822())"
   ><dtml-call "RESPONSE.setHeader('Last-Modified', bobobase_modification_time().toZone('GMT').rfc822())"
   ><dtml-call "RESPONSE.setHeader('If-Modified-Since', bobobase_modification_time().toZone('GMT').rfc822())"
   ><dtml-call "RESPONSE.setHeader('Cache-Control', 'proxy-revalidate')"
></dtml-if>

If the internal control of the caching mechanism shall be considered, the condition for getObjProperty('attr_cacheable', REQUEST) is neccessary.

Pages beyond the Preview are marked as follows:

1. Text files receive a valid date of ca. one day. This means that after download of a page the different systems (local caches and proxy-server) assume that the file is up-to-date for one day. On request a copy of the page is delivered without generating a new file. This is neccessary to be able to deliver complex objects with few time delay.
2. Text files contain a last-modified date with the point in time of the last change.
3. The Proxy at server side is advised to check with every inquiry 'Cache-Control' 'proxy-revalidate'. If the expiry-date has changed, the file is loaded newly. (Mozilla 'Shift'-Reload)
4. The option 'If-Modified-Since' automates this update, but does work only with HTTP 1.1 compatible clients. Regrettably at present all requests are still sent per HTTP 1.0.

It is recomended to apply a template "cache_config" and to call it in the master template (standard_html_header) as well as in the stylesheet resp. possible script templates per "<dtml-var cache_config>".
For the preview-mode a caching beyond ZOME/ZMS is explicitly prevented.

Virtual Host Monster

If several domains shall be maintained within a ZOPE instance, a rewriting of requests is needed. This is taken over within ZOPE by the products SiteAccess or Virtual Host Monster (VHM).
It is to be installed once in the root directory of the server and does not need any further configuration. This reasonablly happens in the Apache configuration, see ZMS Howto 'Apache rewrite'.