Wanted: suggestions on how to invert proxy_pass return codes

[Ruslan Ermilov]

On Tue, Mar 05, 2013 at 12:17:03AM +0000, Jonathan Matthews wrote:
> A slight thinko crept in to my original mail; there's a small
> difference (which does remove a minor complexity) as I've marked below
> ...
> 
> On 4 March 2013 23:58, Jonathan Matthews <contact at jpluscplusm.com> wrote:
> [snip]
> > --------------------------------------------------------------------------
> > location /healthcheck/ {
> >   if (!-f /tmp/flag) {
> >     return 503;
> >   }
> 
> SHOULD BE:
> 
> "
>   if (-f /tmp/flag) {
>     return 200;
>   }
> "
> 
> [snip]
> > --------------------------------------------------------------------------
> >
> > Before making the proxy_pass call, check a marker on disk and serve a
> > (real, not translated to =200) 503 if it exists.
> 
> SHOULD BE: "... serve a 200 if it exists."
> 
> I don't think this changes the meat of the problem - it just removes
> one minor niggle.
> 
> Any thoughts?

Well, if you can add headers on a backend ...

: http {
:     map $connection $fail {
:         ~[02468]$ 1;
:     }
: 
:     server {
:         server_name backend;
:         listen 8001;
:         add_header X-Accel-Redirect /backend_up;
: 
:         if ($fail) { return 503 "real 503\n"; }
:         return 200 "real 200\n";
:     }
: 
:     server {
:         listen 8000;
: 
:         location = /test {
:             proxy_pass http://127.0.0.1:8001;
:             proxy_intercept_errors on;
:             error_page 503 = @backend_down;
:         }
: 
:         location @backend_down {
:             return 200 "wrapped 200\n";
:         }
: 
:         location = /backend_up {
:             internal;
:             return 503 "wrapped 503\n";
:         }
:     }
: }

$ repeat 10 curl http://127.0.0.1:8000/test
wrapped 503
wrapped 200
wrapped 503
wrapped 200
wrapped 503
wrapped 200
wrapped 503
wrapped 200
wrapped 503
wrapped 200

(See http://nginx.org/r/proxy_ignore_headers for the meaning of
X-Accel-Redirect.)