No EXPOSE in aws docker fails deployment

I have a scrapy project run continously by cron hosted inside a docker image.

When I run and deploy this locally everything works fine. If I try to deploy the same to AWS I get the following error inside the logs:

No EXPOSE directive found in Dockerfile, abort deployment (ElasticBeanstalk::ExternalInvocationError)

The console shows that my container was build correctly but I can not use it without an EXPOSED port.

INFO: Successfully pulled python:2.7
WARN: Failed to build Docker image aws_beanstalk/staging-app, retrying...
INFO: Successfully built aws_beanstalk/staging-app
ERROR: No EXPOSE directive found in Dockerfile, abort deployment
ERROR: [Instance: i-6eebaeaf] Command failed on instance. Return code: 1 Output: No EXPOSE directive found in Dockerfile, abort deployment.
Hook /opt/elasticbeanstalk/hooks/appdeploy/enact/00run.sh failed. For more detail, check /var/log/eb-activity.log using console or EB CLI.
INFO: Command execution completed on all instances. Summary: [Successful: 0, Failed: 1].

But why is it not possible?

My Dockerfile looks like the following:

FROM python:2.7
MAINTAINER XDF

ENV DIRECTORY /opt/the-flat

# System
##########

RUN apt-get update -y && apt-get upgrade -y && apt-get install -y ntp vim apt-utils
WORKDIR $DIRECTORY

# GIT
##########
# http://ift.tt/12YvFHs

RUN apt-get install -y git
RUN mkdir /root/.ssh/
ADD deploy/git-deply-key /root/.ssh/id_rsa
RUN chmod 0600 /root/.ssh/id_rsa
RUN touch /root/.ssh/known_hosts
RUN ssh-keyscan -t rsa bitbucket.org >> /root/.ssh/known_hosts
RUN ssh -T -o 'ConnectionAttempts=1' git@bitbucket.org
RUN git clone --verbose git@bitbucket.org:XDF/the-flat.git .

# Install
##########

RUN pip install scrapy
RUN pip install MySQL-python

# not working
# apt-get install -y wkhtmltopdf && pip install pdfkit
# else
# http://ift.tt/1xpfdNR

RUN DEBIAN_FRONTEND=noninteractive apt-get install -y openssl build-essential xorg libssl-dev
RUN wget http://ift.tt/1X14Udt
RUN tar xvjf wkhtmltopdf-0.10.0_rc2-static-amd64.tar.bz2
RUN chown root:root wkhtmltopdf-amd64
RUN mv wkhtmltopdf-amd64 /usr/bin/wkhtmltopdf
RUN pip install pdfkit

# Cron
##########
# http://ift.tt/1M7MK4p
# http://ift.tt/ZDwrU1

RUN apt-get install -y cron
RUN crontab "${DIRECTORY}/deploy/crontab"

CMD ["cron", "-f"]