htaccess: RewriteRule, Tomcat & 503 - apache

Question

Given the following htaccess:
DirectoryIndex
RewriteEngine on
RewriteCond %{HTTPS} !on
RewriteRule .* https://%{SERVER_NAME}%{REQUEST_URI} [R=301,L,QSA]
RewriteRule ^ http://%{HTTP_HOST}:8080%{REQUEST_URI} [P]
If the Tomcat instance is running under Port 8080, the request will be passed.
If the instance is not running, I'm getting an ugly 503-error.
I was trying to replace it with a custom-made page. This works:
ErrorDocument 503 "offline"
but this doesn't:
ErrorDocument 503 /home/www-data/error/503.html
I'm getting:
Additionally, a 503 Service Unavailable error was encountered while trying to use an ErrorDocument to handle the request.
What is the correct solution?

Answer 1

For ErrorDocument you need to give the path of your html page, relative to the document root. So if the DocumentRoot is /home/www-data/ simply set /error/503.html.
Now if this is a .htaccess present in /home/www-data/ then all documents which are children of this directories get the rules applied. So I think even your /error/503.html is treated by your Proxy directive:
RewriteRule ^ http://%{HTTP_HOST}:8080%{REQUEST_URI} [P]
Would be instead:
RewriteCond %{ENV:REDIRECT_STATUS} !=503
RewriteRule ^ http://%{HTTP_HOST}:8080%{REQUEST_URI} [P]
I think it should be enough, or you can exclude /error from the matching path.