Using error_page to a named location - possible?

[Maxim Dounin]

Hello!

On Tue, Mar 06, 2012 at 10:05:03PM +0400, Max wrote:

> 
> 06 марта 2012, 21:47 от Maxim Dounin <mdounin at mdounin.ru>:
> > Hello!
> > 
> > On Tue, Mar 06, 2012 at 04:37:41PM +0000, Ed W wrote:
> > 
> > > Hi, as part of a larger problem I have a captive portal which grabs
> > > all incoming URLs and after evaluating a bunch of logic redirects
> > > the caller somewhere else.  I use proxy_pass to pass the request to
> > > my cgi code.
> > >
> > > However, I would like to customise the error message in the event
> > > that the upstream daemon is unavailable.  I can't figure out how to
> > > do that affecting part of the incoming URLs.  Is it possible to do
> > > something like "error_page @502_error" in conjunction with
> > > proxy_pass?
> > 
> > Yes, see below.
> > 
> > >
> > > So, I have
> > >
> > > server {
> > >   listen 8000 default_server;
> > >
> > >   root /var/www/cp/htdocs/public;
> > >
> > >   location / {
> > >     proxy_read_timeout 5;
> > >     proxy_pass http://127.0.0.1:3000;
> > >     error_page 502 /502.html;
> > >     proxy_set_header Host $http_host;
> > >     proxy_set_header X-Server-Addr $server_addr;
> > >     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
> > >     proxy_set_header X-Forwarded-HTTPS 0;
> > >     proxy_set_header X-Captive-Portal-Redirect 1;
> > > }
> > >   location /502.html {
> > >     internal;
> > >   }
> > > }
> > >
> > >
> > > However, if I visit "http://somewhere/502.html" I get a 404 response
> > > (presumably matching the location /502.html and the 404 is due to
> > > the "internal"?)
> > 
> > Yes.
> > 
> > > I can't see that it's possible to use something like:
> > >
> > >   location / {
> > >     proxy_pass http://127.0.0.1:3000;
> > >     error_page 502 @502;
> > >   }
> 
> It is possible, you should use the proxy_intercept_errors directive:
> 
> location / {
>     proxy_pass http://127.0.0.1:3000;
>     proxy_intercept_errors on;
>     error_page 502 @502;
> }
> 
> location @502 {
>     # all named locations are internal by default, hence no "internal;"
>     return 502 "Gateway error while servicing $request_uri!\n";
> }

The proxy_intercept_errors isn't needed to handle 502's generated 
by nginx, it's only needed when backend returns the error in 
question and one want to override it.

Maxim Dounin