URL-Rewriting not working

[Francis Daly]

On Sat, Apr 08, 2017 at 06:39:59PM +0530, Ajay Garg wrote:

Hi there,

> However, I am not able to do the proxying if I perform url-rewriting.
> Nothing of the following works ::

Note that if you want to reverse-proxy a back-end web service at a
different part of the url hierarchy to where it believes it is installed,
in general you need the web service to help.

That is, if you want the back-end / to correspond to the front-end /x/,
then if the back-end ever links to something like /a, you will need that
to become translated to /x/a before it leaves the front-end. In general,
the front-end cannot do that translation.

So you may find it easier to configure the back-end to be (or to act as
if it is) installed below /x/ directly.

Otherwise things can go wrong.

What that means is...

> a)
> server {
>         listen 2001;
>         location /78 {
> 
>                         auth_basic 'Restricted';
>                         auth_basic_user_file
> /home/2819163155b64c4c81f8608aa23c9faa/.htpasswd;
>                         proxy_pass http://127.0.0.1:2000;
>                 }
>         }
> ############################################################################
> 
> No URL change happens, and 404 (illegal-file-access) is obtained.

If you request http://1.2.3.4:2001/78, nginx should request
http://127.0.0.1:2000/78, and I guess that the back-end said 404.

What do the back-end logs say?

Can you show a specific "curl" command, with "-v" or "-i", that you can
use to show this error case?

> b)
> ############################################################################
> server {
>         listen 2001;
>         location /78 {
> 
>                         auth_basic 'Restricted';
>                         auth_basic_user_file
> /home/2819163155b64c4c81f8608aa23c9faa/.htpasswd;
>                         proxy_pass http://127.0.0.1:2000/;
>                 }
>         }
> ############################################################################
> 
> No URL change happens, and 404 (illegal-file-access) is obtained.

If you request http://1.2.3.4:2001/78, nginx should request
http://127.0.0.1:2000/. Does the 404 come from nginx or the back-end?

What do the back-end logs say?

(Did you request http://1.2.3.4:2001/78, or http://1.2.3.4:2001/78/ --
because the two urls arl different.)

> c)
> ############################################################################
> server {
>         listen 2001;
>         location /78/ {
> 
>                         auth_basic 'Restricted';
>                         auth_basic_user_file
> /home/2819163155b64c4c81f8608aa23c9faa/.htpasswd;
>                         proxy_pass http://127.0.0.1:2000/;
>                 }
>         }
> ############################################################################
> 
> The URL does changes from http://1.2.3.4:2001/78 to
> http://1.2.3.4:2001/cgi-bin/webproc, but a 404 is obtained.

If you request http://1.2.3.4:2001/78, nginx should return 301
redirecting you to http://1.2.3.4:2001/78/. If you then request
http://1.2.3.4:2001/78/, nginx should request http://127.0.0.1:2000/. I
guess that the back-end then returns 301 redirecting you to
/cgi-bin/webproc. If you request http://1.2.3.4:2001/cgi-bin/webproc,
then nginx should return 404 (because /cgi-bin/webproc does not start
with /78/).

Can you see all of those requests and responses, especially the ones
involving the back-end?

> d)
> ############################################################################
> server {
>         listen 2001;
>         location /78/ {
> 
>                         auth_basic 'Restricted';
>                         auth_basic_user_file
> /home/2819163155b64c4c81f8608aa23c9faa/.htpasswd;
>                         proxy_pass http://127.0.0.1:2000;
>                 }
>         }
> ############################################################################
> 
> No URL change happens, and 404 (illegal-file-access) is obtained.

Similar to a)

> So, I guess c) is the closest to doing a url-rewrite, but I wonder why am I
> getting a 404, even though the URL-change is perfect.

You have multiple possible configurations there. And you have not shown
the details of the requests and responses.

Can you show some requests that you want the client to make of nginx,
and then show the matching requests that you want nginx to make of
the back-end?

You can use "curl" on the nginx machine to make similar requests of the
back-end yourself, to see that actual response details. That might give
a hint as to what, if any, proxy_redirect directives are needed.

> Any ideas please?

Can you configure the web service on port 2000 to believe that all of
its useful urls are below /78/ ? If so, use configuration d).

	f
-- 
Francis Daly        francis at daoine.org