Connect two Docker Containers via SocketIO - docker

Question

I have multiple Docker Containers (Server, Client, AI) running on the same Docker bridge. I want the AI to connect to the Server in order to exchange information with Socket.io.
However, when I try to connect the AI to to the Server via:
sio = socketio.Client()
def main():
sio.connect('http://localhost:4000')
sio.emit('ConnectAI', "TEST")
sio.wait()
print("Setting up Connection...")
time.sleep(10)
asyncio.run(main())
I get an Error saying
socketio.exceptions.ConnectionError: HTTPConnectionPool(host='localhost', port=4000): Max retries exceeded with url: /socket.io/?transport=polling&EIO=4&t=1659336255.2636092 (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f87b70dc7f0>: Failed to establish a new connection: [Errno 111] Connection refused'))
I don't know why the connection gets refused. The machines run on the same network, they both use the same version of socketIO.
Here is my Docker-Compose file:
version: "3.9"
services:
client:
build:
context: ./client
dockerfile: Dockerfile
ports:
- "3000:3000"
server:
build:
context: ./server
dockerfile: Dockerfile
ports:
- "4000:4000"
ai:
build:
context: ./ai
dockerfile: Dockerfile
ports:
- "5000:5000"
And here is my Server Docker:
# Dockerfile
FROM node:14.20.0
WORKDIR /app
COPY . /app
RUN npm install
EXPOSE 4000
CMD npm start
And my AI Docker:
# Dockerfile
FROM python:3.8-slim-buster
WORKDIR /app
COPY requirements.txt requirements.txt
RUN pip3 install -r requirements.txt
COPY . .
EXPOSE 5000
CMD python3 connection.py