Nginx proxy_pass fail on heroku

Question

EDIT: Just figure it out! My configuration is ok. It because my cancellation of CNAME is not valid yet. After a while it automatically map by Nginx.

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I try to url masking with Nginx on heroku. It works great until I use a CNAME on my entry domain.

When I directly keyup https://foobar.herokuapp.com/search-beta, request will be forward to FORWARD_HOST as expect with the url correct. But when I try to access my app with a CNAME (let's say we have a CNAME https://www.foobar.com to https://foobar.herokuapp.com) like https://www.foobar.com/search-beta, the request will be redirect to my FORWARD_HOST.

Is there anything I miss? Can any one give me some tips?

thanks

My Nginx config

daemon off;
    #Heroku dynos have at least 4 cores.
    worker_processes <%= ENV['NGINX_WORKERS'] || 4 %>;

    events {
        use epoll;
        accept_mutex on;
        worker_connections 1024;
    }

    http {
        gzip on;
        gzip_comp_level 2;
        gzip_min_length 512;

        server_tokens off;

        log_format l2met 'measure#nginx.service=$request_time request_id=$http_x_request_id';
        access_log logs/nginx/access.log l2met;
        error_log logs/nginx/error.log;

        include mime.types;
        default_type application/octet-stream;
        sendfile on;

        #Must read the body in 5 seconds.
        client_body_timeout 5;

        upstream app_server {
            server unix:/tmp/nginx.socket fail_timeout=0;
        }

        server {
            listen <%= ENV["PORT"] %>;
            server_name _;
            keepalive_timeout 5;

            location / {
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header Host $http_host;
                proxy_redirect off;
                proxy_pass http://app_server; 
            }

            location /assets {
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                set $proxy_pass http://app_server;
                if ($http_referer ~ "search-beta") {
                    set $proxy_pass <%= ENV["FORWARD_HOST"] %>;
                }

                proxy_pass $proxy_pass;
            }

            location /search-beta {
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header X-Forwarded-For 
                $proxy_add_x_forwarded_for;
                proxy_pass <%= ENV["FORWARD_HOST"] %>;
            }
        }
    }