Using error_page to a named location - possible?

[Maxim Dounin]

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;
>   }
> 
> location @502 {
>   index /502.html;
>   root /var/www;
>   internal;
> }

Try something like:

    location @502 {
        internal;
        root /var/www;
        rewrite ^ /502.html break;
    }

This should work at least for GET requests.

> Does someone have a suggestion on how to customise the error
> response without affecting ANY incoming URLs (they must ALL be
> passed through the proxy under normal working situation)
> 
> (Its occured to me that I could perhaps setup another "server { }"
> block listening on another port, then use a different proxy_pass in
> the "location @502 {}"?  Seems ugly, but would that work?)

This should work too.

Maxim Dounin