Connection refused when connecting to the exposed port on docker container - linux

Question

Dockerfile looks like this:
FROM ubuntu:latest
LABEL Spongebob Dockerpants "s.dockerpants#comcast.net"
RUN apt-get update -y
RUN apt-get install -y python3-pip python3-dev build-essential
#Add source files
COPY . /app
ENV HOME=/app
WORKDIR /app
# Install Python web server and dependencies
RUN pip3 install -r requirements.txt
ENV FLASK_APP=app.py
# Expose port
EXPOSE 8090
#ENTRYPOINT ["python3"]
CMD ["python3", "app.py"]
CMD tail -f /dev/null
I started the container like this:
docker run --name taskman -p 8090:8090 -d task-manager-app:latest
I see the container running, and my localhost listening on 8090:
CORP\n0118236 # a-33jxiw0rv8is5 in ~/docker_pete/flask-task-manager on master*
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c1ac5cb27698 task-manager-app:latest "/bin/sh -c 'tail -f…" About a minute ago Up About a minute 0.0.0.0:8090->8090/tcp taskman
CORP\n0118236 # a-33jxiw0rv8is5 in ~/docker_pete/flask-task-manager on master*
$ sudo netstat -nlp | grep 8090
tcp6 0 0 :::8090 :::* LISTEN 1154/docker-proxy
I tried to reach 8090 on the container via localhost per the docker run command I issued, but get 'connection refused'
CORP\n0118236 # a-33jxiw0rv8is5 in ~/docker_pete/flask-task-manager on master*
$ curl http://localhost:8090
curl: (56) Recv failure: Connection reset by peer
I then inspected the port-binding, and it looks ok:
CORP\n0118236 # a-33jxiw0rv8is5 in ~/docker_pete/flask-task-manager on master*
$ sudo docker port c1ac5cb27698 8090
0.0.0.0:8090
When I do a docker inspect , I see this:
$ docker inspect c1ac5cb27698 | grep -A 55 "NetworkSettings"
"NetworkSettings": {
"Bridge": "",
"SandboxID": "7c2249761e4f48eef373c6744161b0709f312863c94fdc17138913952be698a0",
"HairpinMode": false,
"LinkLocalIPv6Address": "",
"LinkLocalIPv6PrefixLen": 0,
"Ports": {
"8090/tcp": [
{
"HostIp": "0.0.0.0",
"HostPort": "8090"
}
]
},
"SandboxKey": "/var/run/docker/netns/7c2249761e4f",
"SecondaryIPAddresses": null,
"SecondaryIPv6Addresses": null,
"EndpointID": "ea7552d0ba9e8f0c865fa4a0f24781811c7332a1e7473c48e88fa4dbe6e5e05d",
"Gateway": "172.17.0.1",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"IPAddress": "172.17.0.2",
"IPPrefixLen": 16,
"IPv6Gateway": "",
"MacAddress": "02:42:ac:11:00:02",
"Networks": {
"bridge": {
"IPAMConfig": null,
"Links": null,
"Aliases": null,
"NetworkID": "cfb5be57fdeed8a08b1650b5706a00542c5249903ce33052ff3f0d3dab619675",
"EndpointID": "ea7552d0ba9e8f0c865fa4a0f24781811c7332a1e7473c48e88fa4dbe6e5e05d",
"Gateway": "172.17.0.1",
"IPAddress": "172.17.0.2",
"IPPrefixLen": 16,
"IPv6Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"MacAddress": "02:42:ac:11:00:02",
"DriverOpts": null
}
}
}
}
I am able to ping the container from my localhost:
CORP\n0118236 # a-33jxiw0rv8is5 in ~/docker_pete/flask-task-manager on master*
$ ping 172.17.0.2
PING 172.17.0.2 (172.17.0.2) 56(84) bytes of data.
64 bytes from 172.17.0.2: icmp_seq=1 ttl=255 time=0.045 ms
64 bytes from 172.17.0.2: icmp_seq=2 ttl=255 time=0.042 ms
64 bytes from 172.17.0.2: icmp_seq=3 ttl=255 time=0.047 ms
^C
--- 172.17.0.2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2053ms
rtt min/avg/max/mdev = 0.042/0.044/0.047/0.008 ms
Is there anything in the configuration that would be causing these connection refused? Is something wrong with the binding?

Answer 1

Your docker file contains two CMD line, but docker will only honor the latest one.
CMD ["python3", "app.py"]
CMD tail -f /dev/null
The actual command executed inside your container is the tail command, which doesn't bind and listen on the port. You can ping the container because the container is alive with the tail command.