moby/docs/sources/examples/python_web_app.rst

title

Python Web app example

description

Building your own python web app using docker

keywords

docker, example, python, web app

Python Web App

While using Dockerfiles is the preferred way to create maintainable and repeatable images, its useful to know how you can try things out and then commit your live changes to an image.

The goal of this example is to show you how you can modify your own Docker images by making changes to a running container, and then saving the results as a new image. We will do that by making a simple 'hello world' Flask web application image.

Download the initial image

Download the shykes/pybuilder Docker image from the http://index.docker.io registry.

This image contains a buildapp script to download the web app and then pip install any required modules, and a runapp script that finds the app.py and runs it.

$ sudo docker pull shykes/pybuilder

Note

This container was built with a very old version of docker (May 2013 - see shykes/pybuilder ), when the Dockerfile format was different, but the image can still be used now.

Interactively make some modifications

We then start a new container running interactively using the image. First, we set a URL variable that points to a tarball of a simple helloflask web app, and then we run a command contained in the image called buildapp, passing it the $URL variable. The container is given a name pybuilder_run which we will use in the next steps.

While this example is simple, you could run any number of interactive commands, try things out, and then exit when you're done.

$ sudo docker run -i -t --name pybuilder_run shykes/pybuilder bash

$$ URL=http://github.com/shykes/helloflask/archive/master.tar.gz
$$ /usr/local/bin/buildapp $URL
[...]
$$ exit

Commit the container to create a new image

Save the changes we just made in the container to a new image called /builds/github.com/shykes/helloflask/master. You now have 3 different ways to refer to the container: name pybuilder_run, short-id c8b2e8228f11, or long-id c8b2e8228f11b8b3e492cbf9a49923ae66496230056d61e07880dc74c5f495f9.

$ sudo docker commit pybuilder_run /builds/github.com/shykes/helloflask/master
c8b2e8228f11b8b3e492cbf9a49923ae66496230056d61e07880dc74c5f495f9

Run the new image to start the web worker

Use the new image to create a new container with network port 5000 mapped to a local port

$ sudo docker run -d -p 5000 --name web_worker /builds/github.com/shykes/helloflask/master /usr/local/bin/runapp

• "docker run -d " run a command in a new container. We pass "-d" so it runs as a daemon.
• "-p 5000" the web app is going to listen on this port, so it must be mapped from the container to the host system.
• /usr/local/bin/runapp is the command which starts the web app.

View the container logs

View the logs for the new web_worker container and if everything worked as planned you should see the line Running on http://0.0.0.0:5000/ in the log output.

To exit the view without stopping the container, hit Ctrl-C, or open another terminal and continue with the example while watching the result in the logs.

$ sudo docker logs -f web_worker
 * Running on http://0.0.0.0:5000/

See the webapp output

Look up the public-facing port which is NAT-ed. Find the private port used by the container and store it inside of the WEB_PORT variable.

Access the web app using the curl binary. If everything worked as planned you should see the line Hello world! inside of your console.

$ WEB_PORT=$(sudo docker port web_worker 5000 | awk -F: '{ print $2 }')

# install curl if necessary, then ...
$ curl http://127.0.0.1:$WEB_PORT
Hello world!

Clean up example containers and images

$ sudo docker ps --all

List --all the Docker containers. If this container had already finished running, it will still be listed here with a status of 'Exit 0'.

$ sudo docker stop web_worker
$ sudo docker rm web_worker pybuilder_run
$ sudo docker rmi /builds/github.com/shykes/helloflask/master shykes/pybuilder:latest

And now stop the running web worker, and delete the containers, so that we can then delete the images that we used.