PostgreSQL docker: "could not bind IPv6 socket: Cannot assign requested address"

EDIT 2: After a long time, solved! See answer below.

EDIT: I am sorry to say that the the problems went away "on their own" between yesterday and today, without me having done anything. Great non-deterministic lesson to learn here... Bonus fun: the "could not bind IPv6 socket" error still appears in the error logs, so this was probably not even the problem in the first place.

I have a problem with a previously functioning docker PGSQL image. Until an uninspired rebuild yesterday ( :-D ), I've used this build successfully for the last 5+ months.

My system:

• Ubuntu 17.04 64b
• PGSQL 9.6.4
• Docker version 17.11.0-ce, build 1caf76c
• I am mapping host port 5433 to container port 5432

The problem (snippet from the PGSQL logs):

...

LOG: could not bind IPv6 socket: Cannot assign requested address

HINT: Is another postmaster already running on port 5432? If not, wait a few seconds and retry.

...

This is what ss is telling me (when the container is running, obviously):

    $ docker exec -it db ss -atune
    Netid  State      Recv-Q Send-Q     Local Address:Port       Peer Address:Port 
    udp    ESTAB      0      0              127.0.0.1:45876         127.0.0.1:45876  uid:999 ino:147509 sk:00000001 <->
    tcp    LISTEN     0      128            127.0.0.1:5432                  *:*      uid:999 ino:147500 sk:00000002 <->

I've cleaned all docker containers / images, I've reinstalled docker, nothing helped. Who can possibly be using the 5432 port in the container? For that matter, am I reading this correctly, that PGSQL is complaining about the 5432 port being already used in the docker container?

Even if you have no solution, a basic idea of how to proceed with debugging this would be a great help.

EDIT:

postgres.docker file

FROM postgres:9.6.4

ADD bin/postgres-setup.sh /docker-entrypoint-initdb.d/postgres-setup.sh

RUN chmod 755 /docker-entrypoint-initdb.d/postgres-setup.sh && \
    apt-get update && \
    apt-get install -y --no-install-recommends postgresql-plpython3-9.6 python3-pip postgresql-9.6-pldebugger && \
    pip3 install pyexcel pyexcel-xls pyexcel-xlsx pyexcel-xlsxw

After a long time, we finally figured out what was the problem -- adding explanation here, in case it helps others.

Since pgsql listens only to localhost by default, when it is running in the docker container, where we have the port mapping configuration, the external API was not able to connect to the pgsql server.

The solution is to allow pgsql to listen to all IP addresses:

1. Connect to db container shell: $ docker exec -ti db bash

2. Change the configuration file /var/lib/postgresql/data/postgresql.conf to allow pgsql to listen to all IPs: listen_addresses = '*'