I have this Dockerfile:

# Use the official python image
FROM python:3.12

# set the working directory
WORKDIR /app

# copy the current directory contents into the container at /app
COPY . /app

### install libgl
RUN apt update && apt install -y libgl1-mesa-glx && rm -rf /var/lib/apt/lists/*
# install the required packages
RUN pip install -r requirements.txt


# run the server script
CMD ["python", "server.py"]

and i have this docker-compose.yml file:

version: '3'

services:
  mqtt2:
    image: eclipse-mosquitto:latest
    ports:
      - "1883:1883"
      - "9001:9001"
    volumes:
      - ./mosquitto.conf:/mosquitto/config/mosquitto.conf:ro

  server:
    build: .
    depends_on:
      - mqtt2
    environment:
      - MQTT_BROKER=mqtt2
    links:
      - mqtt2

and this is my server.py file:

import paho.mqtt.client as mqtt
import time
import os


MQTT_BROKER = os.getenv('MQTT_BROKER', 'mqtt2')
MQTT_PORT = 1883
#MQTT_PORT = 9001
CAMERA_TOPIC = "camera/image"
CLIENT_TOPIC = "server/message"


def on_connect(client, userdata, flags, rc, properties):
    print("connected with result code " + str(rc))
    client.subscribe(CAMERA_TOPIC)


def on_message(client, userdata, msg):
    print(f"Recieved message on {msg.topic}")
    processed_message = "new message for testing"
    client.publish(CLIENT_TOPIC, processed_message)


client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2)

client.on_connect = on_connect
client.on_message = on_message

client.connect(MQTT_BROKER, MQTT_PORT, 120)
client.loop_start()
try:
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    client.loop_stop()
    client.disconnect()

when i build the docker file locally, it works, but when i want to deploy it to a server, it gives error. the error is related to this line of python code:

client.connect(MQTT_BROKER, MQTT_PORT, 120)

It says: “””Name or service not known.””” what should i do? what is wrong with my codes?

As i said, i tried to build this dockerfile locally with this command:

docker-compose up --build

it works, but when i want to deploy it to a server, i get this error:

"""Name or service not known."""