Hello Docker!

02/11/2018

This post is about working with containers and python web applications. But first, a little bit on containers and their use in a development ecosystem. Docker is a technology that provides abstraction and automation at an operating system level offering reusability, automation control, version control, per review, and testing capabilities.
This virtualization of bare-bones operating systems into containers enables a micro-services model where all the units of work are divided into separate units of work, facilitating scalability, relability and testing. In essence, docker containers allows developers to be accountable for programming features without having to worry about machine dependencies.

The following code blocks gives a walk-through on building a dockerized web app, the hello world of docker.

First create a new directory called “hello_docker” to contain our webserver. Then inside the hello_docker directory create a another directory creatively named “app.” Inside the app directory, create a file called hellodocker.py with the following contents.

from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello_world():
 return 'Hello World!\n'
if __name__ == '__main__':
 app.run(debug=True, host='0.0.0.0')

 

This web server will run off a docker container so lets create a dockerfile that will be used to create our docker image. In the hello_docker directory create a file called Dockerfile with the following contents.

FROM python:3.4
RUN pip install Flask==0.10.1
WORKDIR /app
COPY app /app
CMD ["python", "hellodocker.py"]

 

Dockerfiles contain a set of instructions for docker to create an image to specifications. The first line pulls the python 3 image as a base installation and installs flask, the next lines copy the code from our directory to the image on build and runs the server.

Next to build the sample app run in the terminal,

cd hello_docker
docker build -t hello_docker .
docker run -d -p 5000:5000 hello_docker

 

Docker run with flags -d -p run the app in the background and forward port 5000 in the container to port 5000 on the host. The command should output a hash confirming a successful execution.

Screen Shot 2018-02-11 at 6.41.17 PM

Our docker image is now built and running! To test the application run the following command verifying the message “Hello Docker!”:

curl $(docker-machine ip default):5000
Hello Docker!

 

This walkthrough barely scratched the surface of  some of dockers capabilities so if you are interested in experimenting with docker I’ve listed a few links to get started with.

https://aws.amazon.com/what-are-containers/

https://www.docker.com/

https://docs.docker.com/

https://docs.docker.com/registry/#alternatives

https://hub.docker.com/

Here are a few more helpful cmds.

#To see your all docker containers
docker ps -a

#to see your running docker containers
docker ps

#to see your docker images
docker images

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Python Operating System Calls

12/13/2017

Python’s lightweight dynamic interface is proven excellent for networking, data scraping and gui generating tasks. Python’s powerful and possibly overlooked os module enables you to take a dynamic approach to operating system programming. With python you can read or write to and from files across different areas on your hard drive and interface with the cmd line simply utilizing a few lines of code. This becomes useful in managing dependencies and project states.

First import sys and os

# lister.py
import sys, os

Then we will create a new method lets call it lister which will take an argument root to create our directory tree. The for loop will iterate through each directory containing files and os.walk() will generate a list of directories either top-down or bottom-up. This will print each directory to the command line console encapsulated by braces.

def lister(root):
....for (thisdir, subshere, fileshere) in os.walk(root):
........print('[' + thisdir + ']')

Each directory at its root yields a tuple containing three variables: dirpath, dirnames, filenames. These variables make up a tree-like data structure (where *  represents many).

                                                        Screen Shot 2017-12-13 at 2.06.33 PM.png

The nested for loop iterates through all the files contained by the directory.

........for fname in fileshere:
............path = os.path.join(thisdir, fname)
............print(path)

The path is collected and concatenated with the filename and then printed to the console.

if __name__ == '__main__':
....lister(sys.argv[1])

When lister.py is run the root directory must be called with the root directory to pass as an argument so sys knows where to begin the os walk.

Screen Shot 2017-12-13 at 2.13.26 PM

The resulting output might be similar to the stream below.

Screen Shot 2017-12-13 at 2.12.33 PM.png

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