Docker中如何让客户端和服务器监听同一个端口

Question

This Docker network contains two Java files, a client and a server. The goal is to get the client to send a message to the server.

I have hard-coded the server to listen to the port 7892 . So if I run the server locally outside Docker, it will listen to localhost:7892 . Likewise, I have hard-coded the client to send its message to port 7892 on a passed IP address, and I pass localhost if running locally.

Once I containerize the server and client in Docker, it's a struggle to get the client to send its message to the server. The client will attempt to send its message, but I'm not sure where it's sending it to. The server is listening to some port, but I'm not sure why the two are not connecting to each other.

docker-compose.yml:

version: '3.9'

services:
  server:
    build:
      context: ./
      dockerfile: Dockerfile-project1
    image: project1:latest
    container_name: server
    working_dir: /parallelcomputing
    networks:
      - project1network
    ports:
      - 7892 # this is what I've put in my TCPClient and TCPServer
    command:
      - /bin/bash
      - -c
      - |
        echo "Initialize client...done!"
        cd project1
        java -cp ../socket_programming/target/socket_programming-1.0-SNAPSHOT.jar edu.rit.cs.socket.TCPServer
        tail -f /dev/null

  client:
    image: project1:latest
    container_name: client
    depends_on:
      - server
    working_dir: /parallelcomputing
    networks:
      - project1network
    command:
      - /bin/bash
      - -c
      - |
        echo "Initialize server...done!"
        cd project1
        java -cp ../socket_programming/target/socket_programming-1.0-SNAPSHOT.jar edu.rit.cs.socket.TCPClient affr.csv host.docker.internal
        tail -f /dev/null

networks:
  project1network:

When I run docker ps I can see

0f9857535e5a   project1:latest   "/bin/bash -c 'echo …"   2 minutes ago   Up 2 minutes                             client
71b499a3c71f   project1:latest   "/bin/bash -c 'echo …"   2 minutes ago   Up 2 minutes   0.0.0.0:55000->7892/tcp   server

It appears the server is listening to port 7892 on the docker network localhost (which, according to my understanding, is host.docker.internal ).

In my docker-compose.yml, I try to tell the client to send its message to port 7892 on the docker network local host as well, but it's not working.

client    | IO:Connection refused (Connection refused)

I have tried multiple other port configurations, searched through the networking documentation, but I'm not sure how to get the two to connect?

Answer 1

Likewise, I have hard-coded the client to send its message to port 7892 on a passed IP address, and I pass localhost if running locally.
.... The client will attempt to send its message, but I'm not sure where it's sending it to...

Since you're not providing target IP or hostname, your client implementation is sending request to itself (same docker container).

I'd recommend reading this official Docker Networking in Compose documentation.

For example, suppose your app is in a directory called myapp, and your docker-compose.yml looks like this:

 version: "3.9" services: web: build: . ports: - "8000:8000" db: image: postgres ports: - "8001:5432"

Each container can now look up the hostname web or db and get back the appropriate container's IP address. For example, web's application code could connect to the URL postgres://db:5432 and start using the Postgres database.

Or you can either specify server's hostname and you can use that hostname from client implementation.

version: '3'
services:
  dns:
    hostname: 'server0001'

Then your client application should send request to server0001:7892