Docker port has unwanted port declaration - docker

Question

I am using Docker latest version, here is the output of "docker version"
docker version
Client:
Cloud integration: 1.0.14
Version: 20.10.6
API version: 1.41
Go version: go1.16.3
Git commit: 370c289
Built: Fri Apr 9 22:46:57 2021
OS/Arch: darwin/amd64
Context: default
Experimental: true
Server: Docker Engine - Community
Engine:
Version: 20.10.6
API version: 1.41 (minimum version 1.12)
Go version: go1.13.15
Git commit: 8728dd2
Built: Fri Apr 9 22:44:56 2021
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: 1.4.4
GitCommit: 05f951a3781f4f2c1911b05e61c160e9c30eaa8e
runc:
Version: 1.0.0-rc93
GitCommit: 12644e614e25b05da6fd08a38ffa0cfe1903fdec
docker-init:
Version: 0.19.0
GitCommit: de40ad0
I run a simple python flask images as followed https://docs.docker.com/language/python/build-images/
docker run --publish 5000:5000 python-docker-test
My container has up and run without any problem. The problem is I observed an addition port declaration as below
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
8e8188fe2db3 python-docker-test "python3 -m flask ru…" 4 seconds ago Up 3 seconds 0.0.0.0:5000->5000/tcp, :::5000->5000/tcp test_docker_python-docker-test_1
Or more specifically:
PORTS
0.0.0.0:5000->5000/tcp, :::5000->5000/tcp
Output of docker port command
~$ docker port test_docker_python-docker-test_1 5000
0.0.0.0:5000
:::5000
Question is: Why do we have such :::5000 or generally :::<port_num>? Can we avoid this ?
Problem that I have is my bash script that fetch the output docker port need to be modified a bit. It's not a big deal. I just curious if there are some update in Docker 20.10.3.
Thanks
Alex

Answer 1

0.0.0.0 is the wildcard address in IPv4.
:: is the wildcard address of IPv6.
Docker does it so that it can receive requests from both IPv4 and IPv6 network interfaces.
To only bind port in the IPv4 interface, you have to specify the network interface explicitly.
docker run --publish 0.0.0.0:5000:5000 python-docker-test
Docker doc about networking