Docker process opens TCP port, but connection is refused

Question

How can I run a simple server listening on a port, inside a Docker container?

(In case it matters, this is a MacOS X 10.13.6 host.)

When I run a simple HTTP Server:

python3 -m http.server 8001

the process starts correctly, and it listens correctly on that port (confirmed with telnet localhost 8001).

When I run a Docker container, it also runs the process correctly, but now the connection is refused.

web-api/Dockerfile:

FROM python:3.7
CMD python3 -m http.server 8001

docker-compose.yaml:

version: '3'
services:
  web-api:
    hostname: web-api
    build:
      context: ./web-api/
      dockerfile: Dockerfile
    expose:
      - "8001"
    ports:
      - "8001:8001"
    networks:
      - api_network
networks:
  api_network:
    driver: bridge

When i start the container(s), it is running the HTTP server:

$ docker-compose up --detach --build
Building web-api
[…]

$ docker ps
CONTAINER ID        IMAGE                COMMAND                  CREATED             STATUS              PORTS                    NAMES
1db4cd1daaa4        ipsum_web-api        "/bin/sh -c 'python3…"   8 minutes ago       Up 8 minutes        0.0.0.0:8001->8001/tcp   ipsum_web-api_1

$ docker-machine ssh lorem

docker@lorem:~$ ps -ef | grep http.server
root     12883 12829  0 04:40 ?        00:00:00 python3 -m http.server 8001

docker@lorem:~$ telnet localhost 8001
[connects successfully]
^D

docker@lorem:~$ exit

$ telnet localhost 8001
Trying ::1...
telnet: connect to address ::1: Connection refused
Trying 127.0.0.1...
telnet: connect to address 127.0.0.1: Connection refused
telnet: Unable to connect to remote host

What is configured incorrectly here, such that the server works inside the Docker container; but I get Connection refused on port 8001 when connecting from outside the container on its exposed port?

you are running the container inside the docker machine. so get the ip of the machine and try with that ip. docker-machine ls to list and docker-machine ip <<name>>. I believe thats why it works with localhost when you are inside the machine and refused when you try after the exit. — Barath

Bernard Bernard · Accepted Answer · 2019-05-23T04:53:45

Try telnet lorem 8001.

Your python container is exposed to port 8001 on its docker host, which is the one you ssh into (lorem).

When you run docker, docker-compose or docker-machine commands, it uses the value of DOCKER_HOST to figure out which host to connect to. I presume that your DOCKER_HOST has the same ip as lorem.

Docker process opens TCP port, but connection is refused

1 Answers