Flask example using Docker

This repository is to demonstrate how to create, run, and publish a Docker App. Currently, there is an example for putting a Flask Web App into a Docker Container, making it runnable from any computer with Docker regardless of system, environment, libraries, etc.

What is Docker?

Taken straight from their website:

Docker is a platform for developers and sysadmins to develop, deploy, and run applications with containers. The use of Linux containers to deploy applications is called containerization. Containers are not new, but their use for easily deploying applications is.

Installing Docker

Visit this page: https://docs.docker.com/install/

Avoiding Root Privelige Issues (Mac/Linux)

# Create a docker user group
sudo groupadd docker
# Add yourself to the user group
sudo usermod -aG docker $USER
# Logout (or Ctrl+D) and open new terminal for it to take effect
exit

If you don't want docker to have root privelige by default, just add sudo before every docker command for the rest of this tutorial.

Testing your Docker Install

docker run hello-world

Run my docker app anywhere

Here is an example of running a Docker app I created from anywhere without any environment setup:

docker run -p 80:80 rmccorm4/flask_example:latest

Creating your own Docker Container

Creating Dockerfile

Create a file called Dockerfile.

Add the following to your Dockerfile:

# Use an official Python runtime as a parent image
FROM python:3.6-slim

# Set the working directory to /app
WORKDIR /app

# Copy the current directory contents into the container at /app
ADD . /app

# Install any needed packages specified in requirements.txt
RUN pip install --trusted-host pypi.python.org -r requirements.txt

# Make port 80 available to the world outside this container
EXPOSE 80

# Define environment variable $NAME equal to "FlaskBU"
# This isn't necessary, just demonstrating that you can do this
ENV NAME FlaskBU

# Run app.py when the container launches
CMD ["python", "app.py"]

Creating Flask App

requirements.txt

Our Dockerfile will try to install Python libraries from a requirements.txt file, so create a requirements.txt and just add the word Flask to the first line:

On Mac/Linux, just run:

echo Flask > requirements.txt

app.py

This is the Python code that utilizes the Flask library to ship a Web App super quickly and easily! Normally you would you need the right Python version installed to run someone else's code correctly, and for a Flask App you would need to install Flask using a package manager like pip, but pip would have to be the correct version to install the correct version of Flask and so on...

Docker gets rid of all that version handling and packages everything into a Container that will work the same way for everyone's computers.

app.py should contain:

import os
import socket

from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello():
    html = "<h3>Hello {name}!</h3>" \
           "<b>Container ID:</b> {hostname}<br/>" \
           "<img src={image} alt={image}>"

    return html.format(name="Docker", hostname=socket.gethostname(), image='/static/head.jpg')

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=80)

Make sure you create a static directory containing the image of your choice to be displayed on your flask app. I have chosen head.jpg for example, and placed it in the static/ directory.

Building Container

We need to "build" the docker container to put everything together

# Creates an image named hello
docker build -t FlaskBU .

Running Container

We're going to run our container to make sure it worked correctly:

# Run your local image
docker run -p 80:80 FlaskBU

Publishing Container

Now we're going to make this Docker Container public so anyone can run it.

Create a Docker Account

Go to this website to create a Docker account so you can publish your Docker container:

https://hub.docker.com/login

Login to Docker Account

docker login

Push to a Repository

docker push YOUR_USERNAME/FlaskBU:latest

Running your Published Container

docker run -p 80:80 YOUR_USERNAME/FlaskBU:latest

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