Running python program on docker

Question

I'm newbie using Docker and Python and I'd like some help. I'm trying to run a Python program inside a Docker container. This program needs to run periodically, so my approach was, after cloning and installing my program, to run it as a cron job. I created the Dockerfile with all the steps but it's not working. I tried entering the container to run the application but it shows me this error:

root@84592d72d4f0:/bsnap/bsnap# bsnap
Traceback (most recent call last):
  File "/usr/local/bin/bsnap", line 9, in <module>
    load_entry_point('bsnap==1.1', 'console_scripts', 'bsnap')()
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 522, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2647, in load_entry_point
    return ep.load()
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2320, in load
    return self.resolve()
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2326, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "build/bdist.linux-x86_64/egg/bsnap/app.py", line 27, in <module>
  File "build/bdist.linux-x86_64/egg/bsnap/log.py", line 33, in <module>
  File "/usr/local/lib/python2.7/logging/handlers.py", line 760, in __init__
    self._connect_unixsocket(address)
  File "/usr/local/lib/python2.7/logging/handlers.py", line 788, in _connect_unixsocket
    self.socket.connect(address)
  File "/usr/local/lib/python2.7/socket.py", line 224, in meth
    return getattr(self._sock,name)(*args)
socket.error: [Errno 2] No such file or directory

This is my Dockerfile:

FROM ubuntu:14.04

MAINTAINER Dave J. Franco 

RUN echo "deb http://archive.ubuntu.com/ubuntu/ $(lsb_release -sc) main universe" >> /etc/apt/sources.list

RUN apt-get update && apt-get upgrade -y

#Install container essentials
RUN apt-get install -y tar \
                   git \
                   curl \
                   nano \
                   wget \
                   dialog \
                   net-tools \
                   build-essential
# Install pip's dependency: setuptools:
RUN apt-get install -y python python-dev python-distribute python-pip

#git clone project
RUN git clone https://github.com/davejfranco/bsnap.git

#ADD the bsnap configuration file
ADD bsnap.conf /bsnap/bsnap/bsnap.conf

WORKDIR /bsnap

#Install bsnap
RUN python setup.py install

#Add an entry on crontab to execute the script every week 
RUN echo "30 16 09 04 * root /usr/local/bin/bsnap" >> /etc/crontab

Could it be related to some address in bsnap.conf? Also cron would not work in this container (and it should not be used in docker in most cases). — ISanych
– ISanych, Commented Apr 10, 2015 at 16:17

Nathaniel Waisbrot · Accepted Answer · 2015-04-11 04:02:34Z

"I created the Docker file with all the steps but it's not working"

No, your Dockerfile is missing a CMD (or ENTRYPOINT) directive, so Docker doesn't know what to run when you start the container.

You could run a command that does nothing, and then wait for cron to do its thing. Or you could write a cron script yourself:

#!/bin/bash
mins=0
while true; do
 if [ $mins -lt 10080 ]; then
    sleep 60
    mins=$[mins+1]
 else
    /bsnap/bsnap/bsnap
    mins=0
 fi
done

Or you could make your Dockerfile say CMD /bsnap/bsnap/bsnap and then use cron in your host machine to run the container every week. That is how I'd do it, and I believe it's the most Docker-ish path.

"this is my Dockerfile"

You should consider using the official Python container, rather than starting from scratch. It makes it clearer that you're using Python 2.7 and it builds faster (because it's downloading, rather than building more things).

"I tried entering in the instance to run the application but it shows me this"

Here's where the error comes from (GitHib link). Bsnap expects /dev/log to exist, but it doesn't on the Docker container. If it does exist on your host and you want to use it, you could pass -v /dev/log:/dev/log to expose it inside the container. Otherwise, you might need to edit the bsnap code to remove the attempt to log that way.

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