Create custom Docker Image works, using the installed mysql-connector-python in a Container does not

Question

I want to deploy a small Python app that connects with a (currently running locally) MySQL server. Within ./fzwk-app/ I created a module database with DBController.py:

class DbController(object):
    def __init__(self):
        self._db_connection = mysql.connector.connect(
            host='localhost',
            user='foo',
            passwd='bar',
            database='mydb'
        )
        self._db_cur = self._db_connection.cursor()
# ...

When running my small app by running ./fzwk-app/__init__.py locally on my dev device, the db connection works just fine. Now I wanted to start deploying to a docker container. First, I set up the Dockerfile like this:

FROM python:3.6
ADD ./fzwk-app/ /
RUN pip3 install mysql-connector
CMD [ "python", "./__init__.py" ]

Building the Docker Image works just fine (docker build -t fzwk-app:0.1 .), but when I try to create and run a container (docker run fzwk-app), I am greeted with the following Python traceback:

Traceback (most recent call last):
  File "./__init__.py", line 21, in <module>
    from database import DbController as db
  File "/database/DbController.py", line 18, in <module>
    import mysql.connector
ModuleNotFoundError: No module named 'mysql'

Where's my mistake?

i guess you just need to expose what port you will expose your container in your computer. try adding EXPOSE <port_number> to your dockerfile and see if that works. EX: EXPOSE 5000 — Marcelo Fonseca
– Marcelo Fonseca, Commented Apr 29, 2019 at 13:35
Thanks for your input, @MarceloFonseca. I am going to look further into creating a whole stack with a decent docker-compose.yml setup; for now my task is just to create an image that will work an run my small Python app... So, no need to expose anything so far... — appfrosch
– appfrosch, Commented Apr 29, 2019 at 13:50

appfrosch · Accepted Answer · 2019-04-29 13:52:33Z

1

I managed to make it work by changing my Dockerfile to

FROM python:3.6
ADD ./fzwk-app/ /fzwk-app/
RUN pip3 install mysql-connector-python
CMD [ "python", "/fzwk-app/__init__.py" ]

So, it seems that pip install mysql-connector-python made the change, I guess (even though I also moved the location of my app on the image, but that's more for a better overview when doing a docker exec -it fzwk-app /bin/bash...

At least now I am getting the expected

_mysql_connector.MySQLInterfaceError: Can't connect to MySQL server on 'localhost' (99)

error cause it can't connect with my db, but for that I am planning on building a stack with docker-compose anyway.

Hope this will help anyone -- if not, it'll probably help future-me :-)

answered Apr 29, 2019 at 13:52

appfrosch

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