Install a maintenance page without restarting apache

These days we are working with fabric to remove some hazard in maintenance.
Recently someone gzip a Data.fs file in production and our customer loose 2 days of work. We choose to use fabric (http://www.nongnu.org/fab/) to limit command line working to the strict minimum.

Now, almost all procedures were added in a fabric factory, from the installation of a development environment to the upgrade of the production server. In this last part, we search a solution to put a maintenance page without have to gain root privileges to restart the apache used in frontend. For static or CGI sites you can use a .htaccess file to override the global rules. For a stopped Zope server it doesn’t help much.

The goal is to use RewriteCond and RewriteRule in a such way that a static HTML file would be displayed when it exists. We can call it ‘maintenance.html‘ and rename it ‘maintenance.html-disabled‘ to let the site be displayed normally.

We start with a virtual host generated by iw.recipe.squid:

<VirtualHost *:80>
   ServerName www.gosseyn.fr

   RewriteEngine On
   RewriteLog /my/path/to/squid/parts/squid/log/rewrite_www.gosseyn.fr.log
   RewriteLogLevel 0

   CustomLog /my/path/to/squid//parts/squid/log/access_www.gosseyn.fr.log common
   ErrorLog /my/path/to/squid//parts/squid/log/error_www.gosseyn.fr.log

   ## common rules for squid rewrite rules
   RewriteRule ^(.*)$ - [E=BACKEND_LOCATION:127.0.0.1]
   RewriteRule ^(.*)$ - [E=BACKEND_PORT:8081]
   RewriteRule ^(.*)$ - [E=BACKEND_PATH:site]

   RewriteRule  ^/(.*)/$ http://127.0.0.1:3128/%{ENV:BACKEND_LOCATION}/%{ENV:BACKEND_PORT}/http/%{SERVER_NAME}/80/%{ENV:BACKEND_PATH}/__original_url__/$1 [L,P]
   RewriteRule  ^/(.*)$ http://127.0.0.1:3128/%{ENV:BACKEND_LOCATION}/%{ENV:BACKEND_PORT}/http/%{SERVER_NAME}/80/%{ENV:BACKEND_PATH}/__original_url__/$1 [L,P]

   ## specific rules base on cookie

</VirtualHost>

First we need to declare a document root and to bypass all security rules. We create a new path in the root of our buildout folder called ‘maintenances_pages’.

   DocumentRoot /my/path/to/buildout/prod/maintenance_pages

   <Directory "/my/path/to/buildout/prod/maintenance_pages">
       Options None
       AllowOverride None
       Order allow,deny
       allow from all

       <LimitExcept GET>
           Order allow,deny
           allow from all
       </LimitExcept>
   </Directory>

These declaration should satisfy all paranoid BOFH.
Now create a file called maintenance.html within the folder. All code (javascript, CSS and images) must be embeded, this is a limitation of this approach.
Well, how to detect that a file exist on the filesystem from apache. You can do this with the flag ‘-f’ from the rewrite module:

    RewriteCond /my/path/to/buildout/prod/maintenance_pages/maintenance.html -f

Then redirect all pages to our maintenance page:

   RewriteCond %{REQUEST_URI} !/maintenance.html
   RewriteRule $ /maintenance.html [R=302,L]

We also need to disable the standard rewrite rules. The easier way to do it is to use ‘!-f‘.

   RewriteCond /my/path/to/buildout/prod/maintenance_pages/maintenance.html !-f
   RewriteRule  ^/(.*)/$ http://127.0.0.1:3128/%{ENV:BACKEND_LOCATION}/%{ENV:BACKEND_PORT}/http/%{SERVER_NAME}/80/%{ENV:BACKEND_PATH}/__original_url__/$1 [L,P]
   RewriteCond /my/path/to/buildout/prod/maintenance_pages/maintenance.html !-f
   RewriteRule  ^/(.*)$ http://127.0.0.1:3128/%{ENV:BACKEND_LOCATION}/%{ENV:BACKEND_PORT}/http/%{SERVER_NAME}/80/%{ENV:BACKEND_PATH}/__original_url__/$1 [L,P]

These rules will not be applied anymore when our maintenance file will be name ‘maintenance.html’. Our goal is reached.

The whole virtualhost file look like this:

<VirtualHost *:80>
   ServerName www.gosseyn.fr

   RewriteEngine On
   RewriteLog /my/path/to/squid/parts/squid/log/rewrite_www.gosseyn.fr.log
   RewriteLogLevel 0

   CustomLog /my/path/to/squid//parts/squid/log/access_www.gosseyn.fr.log common
   ErrorLog /my/path/to/squid//parts/squid/log/error_www.gosseyn.fr.log

   DocumentRoot /my/path/to/buildout/prod/maintenance_pages

   <Directory "/my/path/to/buildout/prod/maintenance_pages">
       Options None
       AllowOverride None
       Order allow,deny
       allow from all

       <LimitExcept GET>
           Order allow,deny
           allow from all
       </LimitExcept>
   </Directory>

   ## our maintenance page
   RewriteCond /my/path/to/buildout/prod/maintenance_pages/maintenance.html -f
   RewriteCond %{REQUEST_URI} !/maintenance.html
   RewriteRule $ /maintenance.html [R=302,L]

   ## common rules for squid rewrite rules
   RewriteRule ^(.*)$ - [E=BACKEND_LOCATION:127.0.0.1]
   RewriteRule ^(.*)$ - [E=BACKEND_PORT:8081]
   RewriteRule ^(.*)$ - [E=BACKEND_PATH:site]

   RewriteCond /my/path/to/buildout/prod/maintenance_pages/maintenance.html !-f
   RewriteRule  ^/(.*)/$ http://127.0.0.1:3128/%{ENV:BACKEND_LOCATION}/%{ENV:BACKEND_PORT}/http/%{SERVER_NAME}/80/%{ENV:BACKEND_PATH}/__original_url__/$1 [L,P]
   RewriteCond /my/path/to/buildout/prod/maintenance_pages/maintenance.html !-f
   RewriteRule  ^/(.*)$ http://127.0.0.1:3128/%{ENV:BACKEND_LOCATION}/%{ENV:BACKEND_PORT}/http/%{SERVER_NAME}/80/%{ENV:BACKEND_PATH}/__original_url__/$1 [L,P]

   ## specific rules base on cookie

</VirtualHost>

It will be difficult to include this in a recipe as we modify an existing virtualhost in a very specific way.

As usual, all feedbacks are appreciated.