Dockerize Flask App

In this post, I'm going to create a simple Flask app and will run it inside a docker container.

Requirements

docker - We need to install docker for this. To install docker on your system follow this link.
A Flask app - You can find the sample code here.

The Docker Hub image

Since Docker Hub doesn’t have an official Flask repository (at the time of this writing), I’ll be building my own image. There are some non-official images available but it's generally recommended to make your own Dockerfile.

Let's Create Our Dockerfile

Make Project directory

Start with creating a new directory; let’s call it flask_project:

mkdir flask_web

Our flask_app.py file will look something like this:

# simple Flask app
From flask import Flask

app = Flask(__name__)

@app.route("/hello")
def hello():
 return "hello user!!"

@app.route("/")
def index():
 return "hello. You have arrived at '/'"

if __name == '__main__':
    app.run(debug=True, host='0.0.0.0', port=5005)

Now, we need to include Flask in our requirements.txt file:

Flask==0.10.1

Flask Dockerfile

Inside our project directory, we'll create a file named - Dockerfile. your directory will look something like this -

\-Project
  | 
  |-flask_app.py
  |-Dockerfile
  |-Requirements.txt

Open up the Dockerfile and add following -

FROM ubuntu:16.04

MAINTAINER Damanpreet Singh "daman.4880@gmail.com"

RUN apt-get update -y
RUN apt-get install -y python-pip python-dev build-essential

# We copy just the requirements.txt first to leverage Docker cache
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
ENTRYPOINT [ "python" ]

CMD [ "flask_app.py" ]

Explanation -

FROM ubuntu:16.04 - We are using ubuntu 16.04 as base image

MAINTAINER - Used for author field of image( used when pushing image to docker hub).

RUN - It tells docker to run the commands specified. In our case, the commands are apt-get update and install

COPY - copies file from first parameter( . ) from host to the destination parameter(/app).

ENTRYPOINT -  configures the container to run as an executable; only the last ENTRYPOINT instruction executes.

Building Docker Image

To build docker image from our Dockerfile, run following command -

$docker build -t flask-web-app .

-t - lets you add custom tag name to the image- for me it is flask-web-app.

. - here we need to specify the location of Dockerfile.  Since, I'm in the same directory, I'm using .

Running Docker Image

To run the Docker Image, run following command -

$ docker run -p 5000:5005 flask-web-app

-p is used to specify port forwarding. Here we are specifying docker to forward port no. 5005 of image to port no. 5000 of host OS.

flask-web-app is the name of the image that we want to run.

We can find the container runtime details using following command -

$ docker ps -a

See the Results

To see the results, open the web browser and point it to  http://localhost:5000/