我尝试在docker容器中使用express和MongoDB创建一个小API，但无法连接到数据库：
下面是我连接脚本：

const mongoose = require('mongoose');
const result = require('dotenv').config();
const logger = require('../logger/api.logger');
const { DB_USER, DB_PASS, DB_HOST, DB_PORT, DB_NAME } = process.env

const connect = () => {

    const url = `mongodb://@${DB_HOST}:${DB_PORT}/${DB_NAME}`;
    logger.info("CONNECTION_STRING = " + url);
    
    mongoose.connect(url, {
        useNewUrlParser: true,
        useUnifiedTopology: true,
        dbName: process.env.DB_NAME,
    })

    mongoose.connection.once("open", async () => {
        logger.info("Connected to database");
    });
      
    mongoose.connection.on("error", (err) => {
        logger.error("Error connecting to database  ", err);
    });
}

const disconnect = () => {
    
    if (!mongoose.connection) {
      return;
    }
    
    mongoose.disconnect();

    mongoose.once("close", async () => {
        console.log("Diconnected  to database");
    });
};

module.exports = {
    connect,
    disconnect
}

.env文件：

APP_PORT=3333
DB_NAME=first_db
DB_PORT=2717
DB_HOST=db_container

app.js文件：

const express = require('express');

const cors = require("cors");

const app = express();

app.use(cors());
app.use(express.json());

// Routes
const router = require('./routes/router');
app.use(router);

// DB Connection
const database = require('./database/connection');
database.connect();

module.exports = app;

docker-compose文件：

version: '3.9'

services:
# Mongo DB
  mongo_db:
    image: mongo:latest
    container_name: db_container
    restart: always
    ports:
      - '${DB_PORT}:2717'
    volumes:
      - mongo_db:/data/db
    environment:
      MONGO_INITDB_DATABASE: ${DB_NAME}
      MONGO_INITDB_ROOT_USERNAME: ${DB_USER}
      MONGO_INITDB_ROOT_PASSWORD: ${DB_PASS}
# Node API Service      
  api:
    build: .
    ports:
      - '${APP_PORT}:${APP_PORT}'
    depends_on:
      - mongo_db
    volumes:
      - .:/usr/src/
    env_file:
      - .env
    logging:
      driver: "json-file"
      options:
        max-size: "10m"
        max-file: "5"

volumes:
  mongo_db: {}

但是每次我构建docker镜像并尝试运行它时，都会出现以下错误：

db_container  | {"t":{"$date":"2023-03-17T20:36:51.205+00:00"},"s":"I",  "c":"NETWORK",  "id":23015,   "ctx":"listener","msg":"Listening on","attr":{"address":"0.0.0.0"}}
db_container  | {"t":{"$date":"2023-03-17T20:36:51.205+00:00"},"s":"I",  "c":"NETWORK",  "id":23016,   "ctx":"listener","msg":"Waiting for connections","attr":{"port":27017,"ssl":"off"}}
docker-api-1  | MongooseServerSelectionError: connect ECONNREFUSED 172.23.0.2:2717
docker-api-1  |     at _handleConnectionErrors (/app/node_modules/mongoose/lib/connection.js:755:11)
docker-api-1  |     at NativeConnection.openUri (/app/node_modules/mongoose/lib/connection.js:730:11)
docker-api-1  |     at runNextTicks (node:internal/process/task_queues:60:5)
docker-api-1  |     at listOnTimeout (node:internal/timers:537:9)
docker-api-1  |     at process.processTimers (node:internal/timers:511:7)
docker-api-1  |     at async Object.connect (/app/src/database/connection.js:82:7) {
docker-api-1  |   reason: TopologyDescription {
docker-api-1  |     type: 'Unknown',
docker-api-1  |     servers: Map(1) { 'db_container:2717' => [ServerDescription] },
docker-api-1  |     stale: false,
docker-api-1  |     compatible: true,
docker-api-1  |     heartbeatFrequencyMS: 10000,
docker-api-1  |     localThresholdMS: 15,
docker-api-1  |     setName: null,
docker-api-1  |     maxElectionId: null,
docker-api-1  |     maxSetVersion: null,
docker-api-1  |     commonWireVersion: 0,
docker-api-1  |     logicalSessionTimeoutMinutes: null
docker-api-1  |   },
docker-api-1  |   code: undefined
docker-api-1  | }
docker-api-1 exited with code 1