If the proxy_pass directive is specified with a URI, then when a request is passed to the server, the part of a normalized request URI matching the location is replaced by a URI specified in the directive:
location /name/ {
proxy_pass http://127.0.0.1/remote/;
}
If proxy_pass is specified without a URI, the request URI is passed to the server in the same form as sent by a client when the original request is processed, or the full normalized request URI is passed when processing the changed URI:
location /some/path/ {
proxy_pass http://127.0.0.1;
}

In some cases, the part of a request URI to be replaced cannot be determined:

When location is specified using a regular expression, and also inside named locations.
In these cases, proxy_pass should be specified without a URI.

总结起来就是 proxy_pass 过程中会 使用 proxy_pass 中special 的url 替换命中的url，但是如果location 中存在rewrite 或者 要使用变量 那proxy_pass 中special 的url将不再生效

测试文件

server {
    server_name songtest.com;

    #access_log  /tmp/songtest.log  main;
    listen       80 ;

    location / {

        proxy_pass http://127.0.0.1:8080/zz1;
    }
    location /app {
        proxy_pass http://127.0.0.1:8080;
    }
	# songtest.com/app/1 http://127.0.0.1:8080/app/1
    location /app2 {
        proxy_pass http://127.0.0.1:8080/zz2;
    }
	# songtest.com/app2/1 http://127.0.0.1:8080/zz2/1
    location ^~ /app3 {
        proxy_pass http://127.0.0.1:8080/zz2;
    }
	# songtest.com/app3/1 http://127.0.0.1:8080/zz2/1
    location /app5 {
     rewrite (.*) /users?name=$1 break;
    proxy_pass http://127.0.0.1/useless;
    }
		# songtest.com/app5/1 http://127.0.0.1:8080/users?name=/app5/1
}

openresty 中使用的切忌

以上配置在 openresty 添加lua配置后失效