mirror of https://github.com/docker/docs.git
Updates to Compose getting started guide
- Some wording and formatting tweaks - Use Python 3.4, because it's 2016 - Use Alpine-based images for faster downloads and less disk space usage - Use the list form of `CMD` in the Dockerfile, so it's not wrapped in sh - Remove the `depends_on` from `docker-compose.yml`, as it's not really needed - the web app connects to Redis when it's visited, not on startup - Add a section on updating the app and seeing the changes, because that's the point of mounting the code in! - Add a note about `docker-compose down` Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
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Aanand Prasad
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@ -4,26 +4,25 @@ keywords: documentation, docs, docker, compose, orchestration, containers
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title: Get started with Docker Compose
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---
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On this page you build a simple Python web application running on Docker Compose. The
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application uses the Flask framework and increments a value in Redis. While the
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sample uses Python, the concepts demonstrated here should be understandable even
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if you're not familiar with it.
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On this page you build a simple Python web application running on Docker
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Compose. The application uses the Flask framework and maintains a hit counter in
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Redis. While the sample uses Python, the concepts demonstrated here should be
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understandable even if you're not familiar with it.
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## Prerequisites
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Make sure you have already
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[installed both Docker Engine and Docker Compose](install.md). You
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don't need to install Python, it is provided by a Docker image.
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Make sure you have already [installed both Docker Engine and Docker
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Compose](install.md). You don't need to install Python or Redis, as both are
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provided by Docker images.
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## Step 1: Setup
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1. Create a directory for the project:
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1. Create a directory for the project:
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$ mkdir composetest
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$ cd composetest
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2. With your favorite text editor create a file called `app.py` in your project
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directory.
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2. Create a file called `app.py` in your project directory and paste this in:
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from flask import Flask
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from redis import Redis
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@ -33,82 +32,74 @@ don't need to install Python, it is provided by a Docker image.
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@app.route('/')
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def hello():
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redis.incr('hits')
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return 'Hello World! I have been seen %s times.' % redis.get('hits')
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count = redis.incr('hits')
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return 'Hello World! I have been seen {} times.\n'.format(count)
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if __name__ == "__main__":
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app.run(host="0.0.0.0", debug=True)
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3. Create another file called `requirements.txt` in your project directory and
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add the following:
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3. Create another file called `requirements.txt` in your project directory and
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paste this in:
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flask
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redis
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These define the applications dependencies.
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## Step 2: Create a Docker image
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In this step, you build a new Docker image. The image contains all the
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dependencies the Python application requires, including Python itself.
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1. In your project directory create a file named `Dockerfile` and add the
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following:
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FROM python:2.7
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ADD . /code
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WORKDIR /code
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RUN pip install -r requirements.txt
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CMD python app.py
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This tells Docker to:
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* Build an image starting with the Python 2.7 image.
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* Add the current directory `.` into the path `/code` in the image.
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* Set the working directory to `/code`.
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* Install the Python dependencies.
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* Set the default command for the container to `python app.py`
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<br>
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For more information on how to write Dockerfiles, see the [Docker user guide](/engine/tutorials/dockerimages.md#building-an-image-from-a-dockerfile) and the [Dockerfile reference](/engine/reference/builder.md).
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<br>
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2. Build the image.
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$ docker build -t web .
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This command builds an image named `web` from the contents of the current
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directory. The command automatically locates the `Dockerfile`, `app.py`, and
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`requirements.txt` files.
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These define the application's dependencies.
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## Step 3: Define services
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## Step 2: Create a Dockerfile
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Define a set of services using `docker-compose.yml`:
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In this step, you write a Dockerfile that builds a Docker image. The image
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contains all the dependencies the Python application requires, including Python
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itself.
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Create a file called docker-compose.yml in your project directory and add
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the following:
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In your project directory, create a file named `Dockerfile` and paste the
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following:
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FROM python:3.4-alpine
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ADD . /code
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WORKDIR /code
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RUN pip install -r requirements.txt
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CMD ["python", "app.py"]
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This tells Docker to:
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* Build an image starting with the Python 3.4 image.
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* Add the current directory `.` into the path `/code` in the image.
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* Set the working directory to `/code`.
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* Install the Python dependencies.
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* Set the default command for the container to `python app.py`
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For more information on how to write Dockerfiles, see the [Docker user
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guide](/engine/tutorials/dockerimages.md#building-an-image-from-a-dockerfile)
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and the [Dockerfile reference](/engine/reference/builder.md).
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version: '2'
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services:
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web:
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build: .
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ports:
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- "5000:5000"
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volumes:
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- .:/code
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depends_on:
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- redis
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redis:
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image: redis
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## Step 3: Define services in a Compose file
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Create a file called `docker-compose.yml` in your project directory and paste
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the following:
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version: '2'
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services:
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web:
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build: .
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ports:
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- "5000:5000"
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volumes:
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- .:/code
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redis:
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image: "redis:alpine"
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This Compose file defines two services, `web` and `redis`. The web service:
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* Builds from the `Dockerfile` in the current directory.
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* Forwards the exposed port 5000 on the container to port 5000 on the host machine.
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* Mounts the project directory on the host to `/code` inside the container allowing you to modify the code without having to rebuild the image.
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* Links the web service to the Redis service.
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* Uses an image that's built from the `Dockerfile` in the current directory.
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* Forwards the exposed port 5000 on the container to port 5000 on the host
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machine.
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* Mounts the project directory on the host to `/code` inside the container,
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allowing you to modify the code without having to rebuild the image.
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The `redis` service uses the latest public
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The `redis` service uses a public
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[Redis](https://registry.hub.docker.com/_/redis/) image pulled from the Docker
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Hub registry.
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@ -160,7 +151,22 @@ containers](../engine/tutorials/dockervolumes.md).
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The number should increment.
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## Step 5: Experiment with some other commands
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## Step 5: Update the application
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Because the application code is mounted into the container using a volume, you
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can make changes to its code and see the changes instantly, without having to
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rebuild the image.
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1. Change the greeting in `app.py` and save it. For example:
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return 'Hello from Docker! I have been seen {} times.\n'.format(count)
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2. Refresh the app in your browser. The greeting should be updated, and the
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counter should still be incrementing.
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## Step 6: Experiment with some other commands
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If you want to run your services in the background, you can pass the `-d` flag
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(for "detached" mode) to `docker-compose up` and use `docker-compose ps` to
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@ -169,6 +175,7 @@ see what is currently running:
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$ docker-compose up -d
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Starting composetest_redis_1...
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Starting composetest_web_1...
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$ docker-compose ps
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Name Command State Ports
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-------------------------------------------------------------------
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@ -179,14 +186,20 @@ The `docker-compose run` command allows you to run one-off commands for your
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services. For example, to see what environment variables are available to the
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`web` service:
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docker-compose run web env
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$ docker-compose run web env
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See `docker-compose --help` to see other available commands. You can also install [command completion](completion.md) for the bash and zsh shell, which will also show you available commands.
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If you started Compose with `docker-compose up -d`, you'll probably want to stop
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your services once you've finished with them:
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docker-compose stop
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$ docker-compose stop
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You can bring everything down, removing the containers entirely, with the `down`
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command. Pass `--volumes` to also remove the data volume used by the Redis
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container:
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$ docker-compose down --volumes
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At this point, you have seen the basics of how Compose works.
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