Why does my docker containers freezed up?

Question

I've created 3 containers:

1. A container for publishing messages on MQTT protocol every second using python paho-mqtt

2. A subscriber container

3. A mosquitto server container

Container creation commands:

docker image build -t publisher /path/to/dockerfile folder

docker image build -t subscriber /path/to/dockerfile folder

Publisher container docker file:

FROM python:3.9.7

WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip3 install -r requirements.txt

EXPOSE 1883

COPY . .

CMD [ "python", "app.py" ]

And this is mosquitto container log, that shows it runs properly:

1658502881: mosquitto version 2.0.14 running
1658502881: New connection from 172.17.0.5:53757 on port 1883.
1658502881: New client connected from 172.17.0.5:53757 as python-mqtt-29 (p2, c1, k60).
1658502881: New connection from 172.17.0.4:45437 on port 1883.
1658502881: New client connected from 172.17.0.4:45437 as python-mqtt-12 (p2, c1, k60).

Apparently, everything looks good but The problem is when I run the publisher and subscriber containers (docker run publisher), the terminal app freezes up for about 2,3 minutes and then all the messages show up after that delay.

Again pub and sub containers freeze up for 2,3 minutes.

Could anyone help me with that?

---

Update:

My publisher app

import random
import time
from paho.mqtt import client as mqtt_client

broker = '172.17.0.3'
port = 1883
topic = "python/mqtt"

client_id = f'python-mqtt-{random.randint(0, 1000)}'

def connect_mqtt():
    def on_connect(client, userdata, flags, rc):
        if rc == 0:
            print("Connected to MQTT Broker!")
        else:
            print("Failed to connect, return code %d\n", rc)

    client = mqtt_client.Client(client_id)
    client.on_connect = on_connect
    client.connect(broker, port)
    return client

def publish(client):
    msg_count = 0
    while True:
        time.sleep(1)
        msg = f"messages: {msg_count}"
        result = client.publish(topic, msg)
        # result: [0, 1]
        status = result[0]
        if status == 0:
            print(f"Send `{msg}` to topic `{topic}`")
        else:
            print(f"Failed to send message to topic {topic}")
        msg_count += 1

def run():
    client = connect_mqtt()
    client.loop_start()
    publish(client)

if __name__ == '__main__':
    run()

My subscriber:

import random
import pandas
from paho.mqtt import client as mqtt_client

broker = '172.17.0.3'
port = 1883
topic = "python/mqtt"
client_id = f'python-mqtt-{random.randint(0, 100)}'


def connect_mqtt() -> mqtt_client:
    def on_connect(client, userdata, flags, rc):
        if rc == 0:
            print("Connected to MQTT Broker!")
        else:
            print("Failed to connect, return code %d\n", rc)

    client = mqtt_client.Client(client_id)
    client.on_connect = on_connect
    client.connect(broker, port)
    return client


def subscribe(client: mqtt_client):
    def on_message(client, userdata, msg):
        print(f"Received `{msg.payload.decode()}` from `{msg.topic}` topic")

    client.subscribe(topic)
    client.on_message = on_message


def run():
    client = connect_mqtt()
    subscribe(client)
    client.loop_forever()


if __name__ == '__main__':
    run()