Connection reset by peer when hitting Docker container - docker

Question

I'm having a problem, where I can't send network requests to a Docker container I've created. I've exposed the correct ports, so I'm not sure what other issues could be at fault here.
I have a server running in container alice at localhost:10009:
$ docker exec -it alice bash
bash-4.4# curl localhost:10009
curl: (52) Empty reply from server
Port 10009 is exposed from my container:
$ docker port alice
10009/tcp -> 0.0.0.0:10009
When doing the same curl from my host machine I get a different message:
$ curl localhost:10009
curl: (56) Recv failure: Connection reset by peer

Answer 1

I would check to see if the server application is configured to only listen to requests coming from its "localhost", this check depends on the type of server that you're using which is not mentioned.
an easy check is to start your container as follows:
docker run --network host -d yourimagename
You don't need to worry about port mapping since you're using the host network
then try to curl, if that works, then you'll just need to review your server listening IP setting.
curl localhost:10009

Answer 2

I think there are some problems with #Bouzid Zitouni's answer, according to Docker official documentation:
this is the same level of isolation as if the nginx process were running directly on the Docker host and not in a container
However, if you use the --network host you will not have isolated networking in the container, and the host networking driver only works on Linux hosts.
The problem of Connection refused/reset happens because your Server is listening on 127.0.0.1 inside the container and the port forwarding is going to external IP of the container (e.g. 172.17.0.2).
Solution
In your case you need to run a new container making your server to listen on all interfaces. Example using python http.server :
docker run -p 8000:8000 -it python:3.7-slim python3 -m http.server --bind 0.0.0.0
Note
The option --bind 0.0.0.0 it's specific option of http.server. Probally your server has other ways to specify this.
References:
https://pythonspeed.com/articles/docker-connection-refused/
https://docs.docker.com/network/network-tutorial-host/

Answer 3

I would like to expand on #Bouzid Zitouni's answer. It seems there is indeed an issue with the address(es) the server binds to.
Connection reset by peer usually indicates that one has defined a port mapping for the container that does not point to a listening server. Here is an example to illustrate this:
docker run -p 10009:10009 -it ubuntu bash
Install nmap in container:
apt-get update && apt install -y nmap
Run ncat (localhost only)
# ncat -v --listen localhost 10009
...
Ncat: Listening on 127.0.0.1:10009
Run curl on host:
# curl localhost:10009
curl: (56) Recv failure: Connection reset by peer
You actually get the same result even if you don't have any server process at all.
Run ncat (all IPs)
# ncat -v --listen 10009
...
Ncat: Listening on :::10009
Ncat: Listening on 0.0.0.0:10009
Curl on host connects successfully. Hope that helps.

Answer 4

I faced the same error with the docker container running locally on my machine/laptop.
I ran multiple containers and was using the same port number say 8080 for each container run.
After killing all docker process and restarting docker i am now able to connect to the container on the mentioned port 8080 in my case.
$ sudo service docker stop
Warning: Stopping docker.service, but it can still be activated by:
docker.socket
$ sudo service docker start