Error_page behavior

Hello,

I am struggling to understand the error_page directive behavior:

​server {
listen 80;
listen [::]:80;
server_name example.org;

location /proxied {
    return 418 "Host: $host, Connection: $http_connection";
}

}

server {
listen 80;
listen [::]:80;
server_name example.com;

root /var/ious/files;

error_page 418 = /error_page.html;
proxy_intercept_errors on;

location /proxy {
    proxy_pass http://example.org/proxied;
}

}

​Expected behavior:
->Request to http://example.com/proxy
-> Sub-request to http://example.org/proxied
-> Response HTTP 418
-> Error page for HTTP 418 served http://example.com/error_page.html

Observed behavior:
-> Request to http://example.com/proxy
-> Sub-request to http://example.org/proxied
-> Response HTTP 418
-> Error page HTTP 404 (???)

​The error_page.html​ file exists in the example.com root directory as
any
other file.
No error message in the error_log file (warn level).

​I am running​ nginx v1.8.1.

​What am I doing/understanding wrong?​

B. R.

On Mon, Apr 04, 2016 at 09:36:36PM +0200, B.R. wrote:

Hi there,

I am struggling to understand the error_page directive behavior:

I do not get the full same results that you report, when I use 1.9.2.

Expected behavior:
->Request to http://example.com/proxy
-> Sub-request to http://example.org/proxied
-> Response HTTP 418
-> Error page for HTTP 418 served http://example.com/error_page.html

No. Your “error_page” with “=” eats the 418 status.

Observed behavior:
-> Request to http://example.com/proxy
-> Sub-request to http://example.org/proxied
-> Response HTTP 418

I do get that much.

-> Error page HTTP 404 (???)

I only get 404 if error_page.html does not exist. If it does exist,
I get it with http 200.

Aside from that: I suspect that proxy_intercept_errors does exactly the
opposite of what you think it does.

What happens if you set it “off”?

What am I doing/understanding wrong?

error_page normally does not change the http status. Your extra config
told it to change it.

Cheers,

f

Francis D. [email protected]

On Mon, Apr 04, 2016 at 08:54:12PM +0100, Francis D. wrote:

On Mon, Apr 04, 2016 at 09:36:36PM +0200, B.R. wrote:

Hi there,

-> Error page HTTP 404 (???)

I only get 404 if error_page.html does not exist. If it does exist,
I get it with http 200.

Aside from that: I suspect that proxy_intercept_errors does exactly the
opposite of what you think it does.

Apologies - I was wrong there.

“proxy_intercept_errors on;” means that error_page is used for the
returned http status.

“proxy_intercept_errors off;” means that it is not, and the full
original
status+body gets to the client.

So you had (and have) it the way that you want it to be.

f

Francis D. [email protected]

Whoops!
Minimal test configuration FTW… There was a ‘/’ prefix location block
hidden at the bottow of my server one, with an ugly ‘try_files $uri.php
=404;’ directive…

As notes, though :

I removed the ‘=’ parameter from the error_page directive to simplify,
as
there is no special processing during error handling.
I forgot to update the configuration snippet in the mail.

Let’s be clear about proxy_intercept_errors:
Setting it to ‘on’ enables error processing through error_page.
The default (off) simply propagates the proxy error (status code >= 300)
to
clients.

I should have double/triple/quadruplechecked the configuration before
writing on this ML.
​Thanks for your time Francis! And sorry about that…​

B. R.

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