On this page you build a simple Python web application running on Docker Compose. The application uses the Flask framework and increments a value in Redis. While the sample uses Python, the concepts demonstrated here should be understandable even if you’re not familiar with it.
Make sure you have already installed both Docker Engine and Docker Compose. You don’t need to install Python, it is provided by a Docker image.
Create a directory for the project:
$ mkdir composetest $ cd composetest
With your favorite text editor create a file called
app.py in your project
from flask import Flask from redis import Redis app = Flask(__name__) redis = Redis(host='redis', port=6379) @app.route('/') def hello(): redis.incr('hits') return 'Hello World! I have been seen %s times.' % redis.get('hits') if __name__ == "__main__": app.run(host="0.0.0.0", debug=True)
Create another file called
requirements.txt in your project directory and
add the following:
These define the applications dependencies.
In this step, you build a new Docker image. The image contains all the dependencies the Python application requires, including Python itself.
In your project directory create a file named
Dockerfile and add the
FROM python:2.7 ADD . /code WORKDIR /code RUN pip install -r requirements.txt CMD python app.py
This tells Docker to:
.into the path
/codein the image.
Build the image.
$ docker build -t web .
This command builds an image named
web from the contents of the current
directory. The command automatically locates the
Define a set of services using
Create a file called docker-compose.yml in your project directory and add the following:
version: '2' services: web: build: . ports: - "5000:5000" volumes: - .:/code depends_on: - redis redis: image: redis
This Compose file defines two services,
redis. The web service:
Dockerfilein the current directory.
/codeinside the container allowing you to modify the code without having to rebuild the image.
redis service uses the latest public Redis image pulled from the Docker Hub registry.
From your project directory, start up your application.
$ docker-compose up Pulling image redis... Building web... Starting composetest_redis_1... Starting composetest_web_1... redis_1 |  02 Jan 18:43:35.576 # Server started, Redis version 2.8.3 web_1 | * Running on http://0.0.0.0:5000/ web_1 | * Restarting with stat
Compose pulls a Redis image, builds an image for your code, and start the services you defined.
http://0.0.0.0:5000/in a browser to see the application running.
If you’re using Docker on Linux natively, then the web app should now be
listening on port 5000 on your Docker daemon host. If
doesn’t resolve, you can also try
If you’re using Docker Machine on a Mac, use
docker-machine ip MACHINE_VM to get
the IP address of your Docker host. Then,
open http://MACHINE_VM_IP:5000 in a
You should see a message in your browser saying:
Hello World! I have been seen 1 times.
The number should increment.
If you want to run your services in the background, you can pass the
(for “detached” mode) to
docker-compose up and use
docker-compose ps to
see what is currently running:
$ docker-compose up -d Starting composetest_redis_1... Starting composetest_web_1... $ docker-compose ps Name Command State Ports ------------------------------------------------------------------- composetest_redis_1 /usr/local/bin/run Up composetest_web_1 /bin/sh -c python app.py Up 5000->5000/tcp
docker-compose run command allows you to run one-off commands for your
services. For example, to see what environment variables are available to the
$ docker-compose run web env
docker-compose --help to see other available commands. You can also install command completion for the bash and zsh shell, which will also show you available commands.
If you started Compose with
docker-compose up -d, you’ll probably want to stop
your services once you’ve finished with them:
$ docker-compose stop
At this point, you have seen the basics of how Compose works.