Running a flask application in docker

In this article, we will learn how to run a flask application in a docker container by following these simple steps:

Step 1: Create a simple flask application

First of all, lets create a simple flask application. Save the code shown below as app.py.

from flask import Flask
app = Flask(__name__)
@app.route("/")
def joke():
    return "I haven't slept for three days, because that would be too long"
if __name__ == "__main__":
    app.run(host="0.0.0.0", port=8080)

Step 2: Create a Dockerfile

Now that we have a flask application, let us create a Dockerfile to install the necessary dependencies and run it in a docker container. Save the following code as Dockerfile in the same directory as your app.py.

FROM ubuntu:16.04
RUN apt-get update -y
RUN apt-get install python -y
RUN apt-get install python-pip -y
RUN pip install flask

COPY app.py /home/app.py

ENTRYPOINT FLASK_APP=/home/app.py flask run --host=0.0.0.0

This RUN commands in this Dockerfile installs python, python-pip and flask in our docker container. The COPY command copies the app.py file in our computer to /home directory of our docker container. The ENTRYPOINT command starts the flask application when you run the docker container.

Step 3: Building a docker image

In this step, we will build a docker image using the Dockerfile we created in step 2. Run the following command to build an image:

docker build . -t flask-app

You can verify that this image is created by running

docker images

Step 4: Running the flask app in docker container

We are all set to run our flask application in a docker container. We can do this by running the following command:

docker run -p 8080:5000 flask-app

You should see output like this

Step 5: Testing our application

Open a web browser and go to http://localhost:8080/ to verify that the application is up and running.