Connection To MongoDb running in Docker - mongodb

Question

I'm really new in using Docker and now I'm trying to run a Mongodb in a Docker locally and get a Connection to it. I don't know why but I can't get any Connection.
Setup: I am using a Mac with MacOS Catalina 10.15.4
- Docker Desktop Version 2.2.0.5
My Dockerfile:
FROM ubuntu
RUN apt-get update && apt-get install -y gnupg2
RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
RUN echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' > tee /etc/apt/sources.list.d/mongodb.list
RUN apt-get update
RUN apt-get install -y mongodb
RUN mkdir -p /data/db
EXPOSE 27017
CMD ["--port 27017"]
ENTRYPOINT usr/bin/mongod
after this I run these Commands:
docker build -t testmongodb .
docker run -p 27017:27017 testmongodb
I can see the Image runnig in Docker Desktop
and I try to use Studio 3T to Connect to the Mongodb
my Url for this is: mongodb://localhost:27017/?serverSelectionTimeoutMS=5000&connectTimeoutMS=10000&3t.uriVersion=3&3t.connection.name=localhost%3A27017
The Error I get is:
Connection failed.
SERVER [localhost:27017] (Type: UNKNOWN)
|_/ Connection error (MongoSocketReadException): Prematurely reached end of stream
Details:
Timed out after 5000 ms while waiting to connect. Client view of cluster state is {type=UNKNOWN, servers=[{address=localhost:27017, type=UNKNOWN, state=CONNECTING, exception={com.mongodb.MongoSocketReadException: Prematurely reached end of stream}}]

Answer 1

The mongod instance by default only listens on the loopback interface 127.0.0.1. In this case this means the loopback interface inside the container. To also have it listen for external connections you need to specify a separate ip:
ENTRYPOINT usr/bin/mongod --bind_ip 0.0.0.0
As an aside, rolling your own docker image for something like mongodb, which has an official docker image already, is rarely a good idea unless you know what you're doing or need more than the official image can provide.