nginx rewrite POST request

Question

I need send POST request to my nginx frontend server which should redirect it to upstream servers. In details:

send request to http://192.168.0.10/foo/bar/blah and URL in this request should be changed to http://192.168.0.21[22,23]:8080/foo/blah

upstream myapp {
   server 192.168.0.21:8080;
   server 192.168.0.22:8080;
   server 192.168.0.23:8080;
}

server {
    listen       80;
    server_name  localhost;

   location /foo/bar/blah/ {
      rewrite ^/foo/blah^/ /$1 break;
      proxy_pass http://myapp;
   }

but in nginx error log I see that my request changed from POST to GET and also seems didn't change URL:

"POST /foo/bar/blah HTTP/1.1" 301 185 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64)
"GET /foo/bar/blah/ HTTP/1.1" 404 117 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64) 

How can I keep my POST request and change the URL?

Also about my rewrite rule

      rewrite ^/foo/blah^/ /$1 break;

I found a lot of examples for changing URL and all of them looks the same. And it is really strange for me, how this rewrite rule can change URL from /foo/bar/blah/ to /foo/blah/: in documentaion says: http://nginx.org/en/docs/http/ngx_http_rewrite_module.html#rewrite

If the specified regular expression matches a request URI, URI is changed as specified in the replacement string.

but in my case request URI is /foo/bar/blah/ so regular expression /foo/blah^/ doesn't matches URI, so this rule shouldn't work. Am I right?

Would be helpful any advises.

UPD: fixed:

 location = /foo/bar/blah {
          proxy_pass http://myapp/foo/blah;
       }

Answer 1

My guess, you don't need rewrite.

location /foo/bar/ {
  proxy_pass http://myapp/;
}

This should remove /foo/bar part from proxied URL.