Hello Whale: Getting Started with Docker & Flask

3 min read

ContributorJune 12, 2017

When it comes to learning, I tend to retain info best by doing it myself (and failing many times in the process), and then writing a blog about it. So, surprise: I decided to create a blog explaining how you can get a Flask app up and running with Docker! Doing this on my own helped connect the dots when it came to Docker, so I hope it helps you as well.

You can follow along with my repo here:

https://github.com/ChloeCodesThings/chloe_flask_docker_demo

First, I created a simple Flask application. I started by making a parent directory and naming it chloes_flask_demo.

$ mkdir chloes_flask_demo

$ cd chloes_flask_demo

Then, I made a folder called web. The files for my Flask app are kept in here.

$ mkdir web

$ cd web

Then, I created a file called app.py where I added the following code:

from flask import Flask, render_template
 
app = Flask(__name__)
 
 
@app.route('/')
def hello_whale():
    return render_template("whale_hello.html")
 
if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0')

NOTE: As you can see from my repo and code sample, I added a fun giphy and colorful text to mine. To run a simpler version as you follow along you can add:

from flask import Flask
 
app = Flask(__name__)
 
 
@app.route('/')
def hello_whale():
    return ‘Whale, Hello there!’
 
if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0')

And I’ll save this inside of my web folder.

I need Flask to run this application, so I’ll also need a requirements file. This will hold the software we need to be installed inside the container. I’ll create the following requirements.txt folder inside of web folder as well:

Flask==0.12

Now, I’ll make a Dockerfile that will create our image and then deploy it. Name this Dockerfile and write the following:

FROM ubuntu:latest
RUN apt-get update -y
RUN apt-get install -y python-pip python-dev build-essential
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
ENTRYPOINT ["python"]
CMD ["app.py"]

To build this image, I’ll run:

$ docker build -t flask-sample:latest .

And to run the container, I’ll run:

$ docker run -d -p 5000:5000 flask-sample

Now, if I do a docker ps -a…

Cool! My container is up and running on port 5000! Now, if I go to localhost:5000…

Whale, look at that! There’s my Flask app!

Cool- so, now I Dockerized my Flask app. Let’s run it using Docker Compose.

First we’ll need to remove our container running at port 5000. You can do that by typing docker ps -a, into your terminal, and copying the container ID to write:

docker stop [YOUR CONTAINER NUMBER HERE]

Now, in our flask_demo directory, I need to make a docker-compose.yml with the following in it:

web:
  build: ./web
  ports:
   - "5000:5000"
  volumes:
   - .:/code

That’s it! From our chloe-flask-demo directory, run…

docker-compose up

Now, go to port 5000, and…

Hey, there it is again!

You can run docker ps -a to see the details…

Woo! We did it! We Dockerized our Flask App and ran it inside a Docker container, and we ran our app inside a Docker container using Docker compose.

If you have any questions, feel free to comment below. I hope this makes getting started with Docker and Flask a little easier for you. If you’re getting started with Docker, check out my other Hello, Whale blogs!

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