A more complex example (TCP Server/Client)

1.The objective

In this example, we are creating TWO docker apps. - Docker 1: To run a TCP Server - Docker 2: To run a TCP Clinet that connects to the above server - The server starts and waits for a connection request from client(s)

TCP Docker Example

When a TCP client connects to the server and passes its ID name to the server (e.g. TClient-1, TClient-2), which is passed through a command line.
The server in turn, sends a greeting message to each client Hello from server to TCLinet1---Msg #
Additionally, we can run multiple instances of client docker, and server handles each of them with their own greeting message.

2. Directory structure

Create the following directory structure. Refer to the previous tutorial Hello Docker if you need a refresher.

# we do not need any extra modules other than the standard ones
# so we are removing requirments.txt file completely
tcp-docker-app/
├── server/
│   ├── server.py
│   └── Dockerfile
└── client/
    ├── client.py
    └── Dockerfile

3. File contents

Server (Python)

server/server.py

import socket
import time

HOST = '0.0.0.0'
PORT = 5000

def start_server():
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.bind((HOST, PORT))
        s.listen(1)
        print(f"[SERVER] Listening on {HOST}:{PORT}")
        conn, addr = s.accept()
        with conn:
            print(f"[SERVER] Connected by {addr}")
            counter = 1
            while True:
                message = f"hello-client1-msg {counter}\n"
                conn.sendall(message.encode())
                print(f"[SERVER] Sent: {message.strip()}")
                counter += 1
                time.sleep(1)

if __name__ == "__main__":
    start_server()

Server (Dockerfile)

server/Dockerfile

FROM python:3.10-slim
WORKDIR /app
COPY server.py .
CMD ["python", "server.py"]

Client (Python)

client/client.py

import socket

SERVER_HOST = 'server-container'  # container name of the server
SERVER_PORT = 5000

def start_client():
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        print(f"[CLIENT] Connecting to {SERVER_HOST}:{SERVER_PORT}")
        s.connect((SERVER_HOST, SERVER_PORT))
        while True:
            data = s.recv(1024)
            if not data:
                break
            print(f"[CLIENT] Received: {data.decode().strip()}")

if __name__ == "__main__":
    start_client()

Client (Docker file)

client/Dockerfile

FROM python:3.10-slim
WORKDIR /app
COPY client.py .
CMD ["python", "client.py"]

4. Build docker images

server

cd tcp-docker-app/server
sudo docker build -t tcp-server .

client

cd tcp-docker-app/client
sudo docker build -t tcp-client .

Verify the build

sudo docker images

If everything was built correctly, you should see an output:

REPOSITORY        TAG       IMAGE ID       CREATED              SIZE
tcp-client        latest    3a7e23eb624a   59 seconds ago       127MB
tcp-server        latest    8aa392e6b1e3   About a minute ago   127MB

5. Run (server, client, network)

Create a docker network

sudo docker network create tcp-net

Run the server container

In Terinal-1

sudo docker run  --rm -it --name server-container --network tcp-net tcp-server

Run the Client container (1)

In Terminal-2

sudo docker run --rm -it --name client-container1 --network tcp-net tcp-client python client.py Client-1

Run the Client container (2)