Double port forwarding kubernetes + docker - postgresql

Question

Summary:
I have a docker container which is running kubectl port-forward, forwarding the port (5432) of a postgres service running as a k8s service to a local port (2223).
In the Dockerfile, I have exposed the relevant port 2223. Then I ran the container by publishing the said port (-p 2223:2223)
Now when I am trying to access the postgres through psql -h localhost -p 2223, I am getting the following error:
psql: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
However, when I do docker exec -ti to the said container and run the above psql command, I am able to connect to postgres.
Dockerfile CMD:
EXPOSE 2223
CMD ["bash", "-c", "kubectl -n namespace_test port-forward service/postgres-11-2 2223:5432"]
Docker Run command:
docker run -it --name=k8s-conn-12 -p 2223:2223 my_image_name:latest
Output of the docker run command:
Forwarding from 127.0.0.1:2223 -> 5432
So the port forwarding is successful, and I am able to connect to the postgres instance from inside the docker container. What I am not able to do is to connect from outside the container with the exposed and published port

Answer 1

You are missing a following parameter with your $ kubectl port-forward ...:
--address 0.0.0.0
I've reproduced the setup that you've tried to achieve and this was the reason the connection wasn't possible. I've included more explanation below.
Explanation
$ kubectl port-forward --help
Listen on port 8888 on all addresses, forwarding to 5000 in the pod
kubectl port-forward --address 0.0.0.0 pod/mypod 8888:5000
Options:
--address=[localhost]: Addresses to listen on (comma separated). Only accepts IP addresses or
localhost as a value. When localhost is supplied, kubectl will try to bind on both 127.0.0.1 and ::1
and will fail if neither of these addresses are available to bind.
By default: $ kubectl port-forward will bind to the localhost i.e. 127.0.0.1. In this setup the localhost will be the internal to the container and will not be accessible from your host even with the --publish (-p) parameter.
To allow the connections that are not originating from localhost you will need to pass earlier mentioned: --address 0.0.0.0. This will make kubectl listen on all IP addresses and respond to the traffic accordingly.
Your Dockerfile CMD should look similar to:
CMD ["bash", "-c", "kubectl -n namespace_test port-forward --address 0.0.0.0 service/postgres-11-2 2223:5432"]
Additional reference:
Kubernetes.io: Docs: Reference: Generated: Kubectl commands