fastcgi_intercept_errors & error_page

[Maxim Dounin]

Hello!

On Tue, Nov 06, 2012 at 01:12:05AM +0800, howard chen wrote:

> According to the doc:
> http://wiki.nginx.org/HttpFastcgiModule#fastcgi_intercept_errors
> 
> Note: You need to explicitly define the error_page handler for this for it
> to be useful. As Igor says, "nginx does not intercept an error if there is
> no custom handler for it it does not show its default pages. This allows to
> intercept some errors, while passing others as are."
> 
> Actually I still can't understand the exact meaning, so I have done some
> experimentd.
> 
> 1. turn on fastcgi_intercept_errors,
>     - in the backend php/fcgi send 404 header,
>     - set the error_page (php)
> 
> Result: nginx use the default error template
> 
> 2. turn off fastcgi_intercept_errors,
>     - in the backend php/fcgi send 404 header
>     - set the error_page (php)
> 
> Result: now the custom error_page (php) is being used.

It's unclear how you did your experiments, but results 
are all wrong - most likely, you missed something.

E.g. in (1) I would assume request to the error_page resulted in 
another 404, which in turn resulted in default error page 
returned.

> So it seems to me that* fastcgi_intercept_errors should be off and set
> the error_page *if I need to specify custom error handler, is
> this interoperation correct?

No.

The fastcgi_intercept_errors directive is off by default, and this 
means that nginx won't try to do anything with responses returned 
by backends as long as they are valid.

If you want nginx to change response returned by a backend, you 
have to switch on fastcgi_intercept_errors and configure 
appropriate error_page.  Example configuration:

    error_page 404 /errors/404.html;

    location / {
        fastcgi_pass 127.0.0.1:9000;
        fastcgi_intercept_errors on;
        ...
    }

    location /errors/ {
        # static
    }

With the above config if fastcgi backend returns 404, the 
/errors/404.html will be returned instead (assuming it exists).

-- 
Maxim Dounin
http://nginx.com/support.html