我有一个 docker compose 文件，如下所示：

version: "3.9"
services:
  mysqldb:
    image: mysql:5.7
    container_name: mysqlcontainer
    command: --default-authentication-plugin=mysql_native_password
    volumes:
      - ./db/init.sql:/docker-entrypoint-initdb.d/0_init.sql
    ports:
      - 3306:3306
    expose:
      - 3306
    environment:
      MYSQL_DATABASE: "todos"
      MYSQL_USER: "admin"
      MYSQL_PASSWORD: "password"
      MYSQL_ROOT_PASSWORD: "password"
      SERVICE_TAGS: dev
      SERVICE_NAME: mysqldb
    restart: on-failure
    networks:
      - internalnet
  expressapp:
    container_name: api
    build: .
    image: expressapp:1.0
    ports:
      - "3001:3001"
    expose:
      - "3001"
    environment:
      DB_HOST: mysqldb
      DB_PORT: 3306
      DB_USER: "admin"
      DB_PASSWORD: "password"
      DB_NAME: todos
      DB_CONNECTION_LIMIT: 20
      SERVICE_TAGS: dev
      SERVICE_NAME: expressapp
      PORT: 3001
    depends_on:
      - mysqldb
    networks:
      - internalnet
networks:
  internalnet:
    driver: bridge
volumes:
  database:

如果我使用 docker compose up -d 命令启动容器并使用 ps 命令检查正在运行的容器，我将得到以下输出：

CONTAINER ID   IMAGE            COMMAND                  CREATED         STATUS         PORTS                               NAMES
9f338b733a1c   expressapp:1.0   "docker-entrypoint.s…"   2 minutes ago   Up 2 minutes   0.0.0.0:3001->3001/tcp              api
edef8027dc0a   mysql:5.7        "docker-entrypoint.s…"   2 minutes ago   Up 2 minutes   0.0.0.0:3306->3306/tcp, 33060/tcp   mysqlcontainer

但是当我尝试向服务器发出 API 请求时，我收到以下错误消息：

"There was an error processing your request: connect ECONNREFUSED 172.24.0.2:3306"

为什么是因为我将 DB_HOST 变量设置为 mysql 服务名称？