Step 1: Setup
Create a directory for the project:
$ mkdir composetest $ cd composetest
With your favorite text editor create a file called
app.pyin your project directory.
from flask import Flaskfrom 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.txtin your project directory and add the following:
These define the applications dependencies.
Step 2: Create a Docker image
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
Dockerfileand add the following:
FROM python:2.7ADD . /codeWORKDIR /codeRUN pip install -r requirements.txtCMD python app.py
This tells Docker to:
Build an image starting with the Python 2.7 image.
Add the current directory
.into the path
/codein the image.
Set the working directory to
Install the Python dependencies.
Set the default command for the container to
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
Step 3: Define services
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:
Builds from the
Dockerfilein the current directory.
Forwards the exposed port 5000 on the container to port 5000 on the host machine.
Mounts the project directory on the host to
/codeinside the container allowing you to modify the code without having to rebuild the image.
Links the web service to the Redis service.
redis service uses the latest public Redis image pulled from the Docker Hub registry.
Step 4: Build and run your app with Compose
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 2.8.3web_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 http://0.0.0.0:5000doesn’t resolve, you can also try http://localhost:5000.
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 browser.
You should see a message in your browser saying:
Hello World! I have been seen 1 times.
Refresh the page.
The number should increment.
Step 5: Experiment with some other commands
If you want to run your services in the background, you can pass the
-d flag (for “detached” mode) to
docker-compose up and use
docker-compose psto 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.