Microk8s + Flask [part 1]

Dockerize a Flask application

3 min readJul 19, 2019

Over the past couple of weeks, I had been struggling with exposing a simple, custom Flask application in Microk8s. After managing to do so, I have decided to share my story with you, hoping it will be useful for similar purposes.

Overview

In this story (part 1), I will basically cover two tasks:

I will show you the application I have developed. It is by far one of the simplest I have ever built though 😛.
Following, I will create a docker image for the app, using a dockerfile.

In the part 2, we will be covering how this app can be exposed as a Service in Microk8s.

The application

So, let’s see the application itself, which is basically a Flask app that only renders an HTML template and uses some CSS.

App Structure

Assuming the application is inside a directory called “my-app”, there is:

The app.py file

from flask import Flask, render_template
app = Flask(__name__)@app.route(‘/’)
def index():
 return render_template(“index.html”)if __name__ == ‘__main__’:
 app.run(debug = True, host=’0.0.0.0')

A /templates directory including the index.html file which will be rendered.

<!DOCTYPE html>
<html lang=”en”><head>
    <meta charset=”UTF-8">
    <meta name=”viewport” content=”width=device-width, initial-scale=1.0">
    <meta http-equiv=”X-UA-Compatible” content=”ie=edge”>
    <link rel=”stylesheet” href=”{{ url_for(‘static’, filename=’css/styles.css’) }}”> 
    <title>my-app</title>
</head><body>
    <div class=”container”>
        <h1>My App</h1>
        <h3>This app will be a Kubernetes deployment and …</h3>
        <h3>… then it will be exposed as a service</h3>
    </div>
</body></html>

The /static/css directory with a styles.css file inside.

html{
  height: 100%;
}body{
  height: 100%;
  margin: 0;
  padding: 0;
  background-color: #483d8d;
  display: flex;  
  align-items: center; /* center of page */
  justify-content: center; /* center of page */
}.container{
  background-color: #efcfcb;
  border-radius: 10px;
  padding: 2rem;
  box-sizing: border-box;
}.container h1{
  color: #172727;  
  font-family: 'Abril Fatface', sans-serif;
}.container h3{
  font-family: 'DM Sans', sans-serif;
  color: #2f4f4f;
}

Dockerizing the Application

Dockerfile

The first part of the process was creating a dockerfile, with the following lines, each of which is explained with comments right above it:

# with this line we import python language.
FROM python:2.7# copy the requirements.txt file in the image
COPY ./requirements.txt /app/requirements.txt# the working directory will be the /app directory which can be 
# found inside the python image
WORKDIR /app# let's install the requirements (only Flask is needed)
RUN pip install -r requirements.txt# we can now add our directory to the working directory
COPY ./my-app/ /app# let's run the application
CMD [ "python","app.py" ]

Requirements.txt file

The requirements file contains only a single line. Well, actually only a single word:

Flask

Let’s create the image

First, we must put the dockerfile and the requirements file where the directory “my-app” is.

We can now create the image with the following line of code:

docker build -t flask-docker-image .

After running the command, we can check for the newly created docker image. We can run:

docker images

Then, we should see the following outcome:

And now, we are absolutely ready to go to the next level!

To find out how we can actually deploy the application in Microk8s, take a look at the second part of this story.