local http = require "http"
local httpc = http.new()

token = "abc123"
out_trade_no = "456"

--url = "http://【【IP地址】】/Control_center/api.php/Sself/get?token="..token.."&out_trade_no="..out_trade_no

url = "http://【【域名】】/Control_center/api.php/Sself/get?token="..token.."&out_trade_no="..out_trade_no

local res, err = httpc:request_uri(url, {
method = "GET",
headers = {
["Content-Type"] = "application/x-www-form-urlencoded",
}
})

if not res then
ngx.say("failed to request: ", err)
return
end

ngx.status = res.status

for k,v in pairs(res.headers) do
ngx.say(k..'----'..v)
end

ngx.say(res.body)

结果：
用ip拼接的地址，返回正常的数据
用域名拼接的地址，返回的 no resolver defined to resolve 域名 比如 "www.baidu.com"
我配置过resolver 8.8.8.8; 结果还是一样

nginx.conf配置文件
#user nobody;
worker_processes 1; #nginx worker 数量

error_log logs/error.log;

error_log logs/error.log notice;

error_log logs/error.log info;

pid logs/nginx.pid;

events {
worker_connections 1024;
}

http {
resolver 223.5.5.5 223.6.6.6 1.2.4.8 114.114.114.114 valid=3600s;
include mime.types;
default_type application/octet-stream;

#log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
#                  '$status $body_bytes_sent "$http_referer" '
#                  '"$http_user_agent" "$http_x_forwarded_for"';

lua_package_path "/usr/local/openresty/lualib/resty/?.lua;;";
lua_package_cpath "/usr/local/openresty/lualib/resty/?.so;;";
include /usr/local/openresty/nginx/html/Control_center/c_c.conf;

#access_log  logs/access.log  main;

sendfile        on;
#tcp_nopush     on;

#keepalive_timeout  0;
keepalive_timeout  65;

#gzip  on;

server {
    listen       80;
    server_name  localhost;

    #charset koi8-r;

    #access_log  logs/host.access.log  main;

    location / {
        root   html;
        index  index.html index.htm;
    }

    location /lua {
        default_type 'text/html';
        content_by_lua 'ngx.say("Hello Lua!")';
    }


    #error_page  404              /404.html;

    # redirect server error pages to the static page /50x.html
    #
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   html;
    }

    # proxy the PHP scripts to Apache listening on 127.0.0.1:80
    #
    #location ~ \.php$ {
    #    proxy_pass   http://127.0.0.1;
    #}

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    #location ~ \.php$ {
    #    root           html;
    #    fastcgi_pass   127.0.0.1:9000;
    #    fastcgi_index  index.php;
    #    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
    #    include        fastcgi_params;
    #}

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    #location ~ /\.ht {
    #    deny  all;
    #}
}

# another virtual host using mix of IP-, name-, and port-based configuration

# server {
    # listen       8000;
    # listen       somename:8080;
    # server_name  somename  alias  another.alias;

    # location / {
        # root   html;
        # index  index.html index.htm;
    #}
#}

# HTTPS server
#
#server {
#    listen       443 ssl;
#    server_name  localhost;

#    ssl_certificate      cert.pem;
#    ssl_certificate_key  cert.key;

#    ssl_session_cache    shared:SSL:1m;
#    ssl_session_timeout  5m;

#    ssl_ciphers  HIGH:!aNULL:!MD5;
#    ssl_prefer_server_ciphers  on;

#    location / {
#        root   html;
#        index  index.html index.htm;
#    }
#}

}