MQTT Connection in Docker Container

Question

I have a Docker Compose File, which creates multiple Containers. One container wih the mqtt broker:

mqtt:
    image: eclipse-mosquitto
    hostname: mosquitto
    container_name: mqtt
    restart: unless-stopped
    ports:
        - "1883:1883"
        - "9001:9001"
    volumes:
        - ./mosquitto:/etc/mosquitto/
        healthcheck:
            test: ["CMD", "mosquitto_sub", "-t", "$$SYS/#", "-C", "1", "-i", "healthcheck", "-W", "3"]
            interval: 10s
            retries: 5
            start_period: 30s
            timeout: 10s

And one Python container which uses paho to connect to the Broker:

MQTT_SERVER = "host.docker.internal"
MQTT_PATH = "test_channel"


def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))


def on_message(client, userdata, msg):
    print("Message received")



client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect(MQTT_SERVER, int(str(os.environ["MQTT_PORT"])), keepalive=60)

client.subscribe(MQTT_PATH)

client.loop_forever()

I then send with another python file from my PC (not in a docker Container) messages:

import json
import random
import time

import paho.mqtt.publish as publish
import datetime

MQTT_SERVER = "localhost"
MQTT_PATH = "test_channel"


while True:

    data = {
        "1" :1,
        "2" : 2
    }

    message = {
        "source": "source1",
        "data": data,
        "time": datetime.datetime.now(datetime.timezone.utc).strftime("%Y-%m-%d %H:%M:%S.%f")
    }


    publish.single(MQTT_PATH, json.dumps(message), hostname=MQTT_SERVER)

    time.sleep(0.1)

The messages get through and I can recieve them but it stops working after the keep_alive time. I guess the listener cant communicate with the broker.

I changed the keep_alive time and confirmed that this is the Problem.

Anyone knows how I can fix this?