node + Swagger behind nginx proxy_pass

I'm trying to get node and swagger to work with nginx dynamically

server_name ~^backend(?<PORTSERVER>[^.]+)\.domain\.com$;

location /swagger
{
proxy_pass http://127.0.0.1:$PORTSERVER/swagger/;
}

location /api
{
proxy_pass http://127.0.0.1:$PORTSERVER/api;
}

this is an example of virtual host the PORTSERVER variable is taking from gitlab-ci it takes id number of merge request + 2000

when i put the port directly in place of $PORTSEVER every thing is working swagger and api

any advice is appreciated thank you

this is index.js file

    "use strict";
var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};
Object.defineProperty(exports, "__esModule", { value: true });
require("reflect-metadata");
const typeorm_1 = require("typeorm");
const express = require("express");
// var router = express.Router();
const fileUpload = require("express-fileupload");
const bodyParser = require("body-parser");
const routes_1 = require("./routes");
const cors = require("cors");
const typeorm_pagination_1 = require("typeorm-pagination");
const swaggerUi = require('swagger-ui-express');
const swaggerDocument = require('../../swagger.json');
var path = require('path');
typeorm_1.createConnection()
    .then((connection) => __awaiter(void 0, void 0, void 0, function* () {
    // create express app
    const app = express();
    app.use(bodyParser.json());
    app.use(bodyParser.urlencoded());
    app.use(fileUpload());
    app.use(express.static(path.join(__dirname, '..', 'public')));
    console.log(path.join(__dirname, '..', 'public'));
    // register express routes from defined application routes
    routes_1.Routes.forEach((route) => {
        app[route.method]('/api' + route.route, (req, res, next) => {
            const result = new route.controller()[route.action](req, res, next);
            res.header('Access-Control-Allow-Origin', '*');
            if (result instanceof Promise) {
                result.then((result) => (result !== null && result !== undefined ? res.send(result) : undefined));
            }
            else if (result !== null && result !== undefined) {
                res.json(result);
            }
        });
    });
   // setup express app here
    // ...
    app.use('/swagger', swaggerUi.serve, swaggerUi.setup(swaggerDocument));
    app.use(express.json());
    app.use(cors());
    app.use(typeorm_pagination_1.pagination); // Register the pagination middleware
    // start express server
 //   app.listen(process.env.SERVER_Port);
    app.listen(process.env.PORTSERVER);
    console.log('Express server has started on port ' + process.env.PORTSERVER);
}))
    .catch((error) => console.log(error));
//# sourceMappingURL=index.js.map