rejig the helloflask example as more advanced, and move it to the end

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)

docs/sources/examples/index.rst

@@ -16,7 +16,6 @@ to more substantial services like those which you might find in production.
    :maxdepth: 1
 
    hello_world
-   python_web_app
    nodejs_web_app
    running_redis_service
    running_ssh_service
@@ -26,3 +25,4 @@ to more substantial services like those which you might find in production.
    running_riak_service
    using_supervisord
    cfengine_process_management
+   python_web_app

docs/sources/examples/python_web_app.rst

@@ -9,85 +9,86 @@ Python Web App
 
 .. include:: example_header.inc
 
-The goal of this example is to show you how you can author your own
-Docker images using a parent image, making changes to it, and then
-saving the results as a new image. We will do that by making a simple
-hello Flask web application image.
+While using Dockerfiles is the prefered 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.
 
 **Steps:**
 
 .. code-block:: bash
 
-    sudo docker pull shykes/pybuilder
+    $ sudo docker pull shykes/pybuilder
+
+Download the ``shykes/pybuilder`` Docker image from the ``http://index.docker.io``
+registry. Note that this container was built with a very old version of docker 
+(May 2013), but can still be used now.
 
-We are downloading the ``shykes/pybuilder`` Docker image
 
 .. code-block:: bash
 
-    URL=http://github.com/shykes/helloflask/archive/master.tar.gz
+    $ sudo docker run -i -t -name pybuilder_run shykes/pybuilder bash
 
-We set a ``URL`` variable that points to a tarball of a simple helloflask web app
+    $$ URL=http://github.com/shykes/helloflask/archive/master.tar.gz
+    $$ /usr/local/bin/buildapp $URL
+    [lots of output later]
+    $$ exit
+
+
+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.
 
 .. code-block:: bash
 
-    BUILD_JOB=$(sudo docker run -d -t shykes/pybuilder:latest /usr/local/bin/buildapp $URL)
-
-Inside of the ``shykes/pybuilder`` image there is a command called
-``buildapp``, we are running that command and passing the ``$URL`` variable
-from step 2 to it, and running the whole thing inside of a new
-container. The ``BUILD_JOB`` environment variable will be set with the new container ID.
-
-.. code-block:: bash
-
-    sudo docker attach -sig-proxy=false $BUILD_JOB
-    [...]
-
-While this container is running, we can attach to the new container to
-see what is going on. The flag ``--sig-proxy`` set as ``false`` allows you to connect and
-disconnect (Ctrl-C) to it without stopping the container.
-
-.. code-block:: bash
-
-    sudo docker ps -a
-
-List all Docker containers. If this container has already finished
-running, it will still be listed here.
-
-.. code-block:: bash
-
-    BUILD_IMG=$(sudo docker commit $BUILD_JOB _/builds/github.com/shykes/helloflask/master)
+    $ sudo docker commit pybuilder_run /builds/github.com/shykes/helloflask/master
+    c8b2e8228f11b8b3e492cbf9a49923ae66496230056d61e07880dc74c5f495f9
 
 Save the changes we just made in the container to a new image called
-``_/builds/github.com/hykes/helloflask/master`` and save the image ID in
-the ``BUILD_IMG`` variable name.
+``/builds/github.com/hykes/helloflask/master``. You now have 3 different
+ways to refer to the container, name, short-id ``c8b2e8228f11``, or 
+long-id ``c8b2e8228f11b8b3e492cbf9a49923ae66496230056d61e07880dc74c5f495f9``.
 
 .. code-block:: bash
 
-    WEB_WORKER=$(sudo docker run -d -p 5000 $BUILD_IMG /usr/local/bin/runapp)
+    $ WEB_WORKER=$(sudo docker run -d -p 5000 /builds/github.com/hykes/helloflask/master /usr/local/bin/runapp)
+
+Use the new image to create a new container with
+network port 5000, and return the container ID and store in the
+``WEB_WORKER`` variable (rather than naming a container/image, you can use the ID's).
 
 - **"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.
-- **"$BUILD_IMG"** is the image we want to run the command inside of.
 - **/usr/local/bin/runapp** is the command which starts the web app.
 
-Use the new image we just created and create a new container with
-network port 5000, and return the container ID and store in the
-``WEB_WORKER`` variable.
 
 .. code-block:: bash
 
-    sudo docker logs $WEB_WORKER
+    $ sudo docker logs -f $WEB_WORKER
      * Running on http://0.0.0.0:5000/
 
 View the logs for the new container using the ``WEB_WORKER`` variable, 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.
+
 .. code-block:: bash
 
-    WEB_PORT=$(sudo docker port $WEB_WORKER 5000 | awk -F: '{ print $2 }')
+    $ WEB_PORT=$(sudo docker port $WEB_WORKER 5000 | awk -F: '{ print $2 }')
 
 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.
@@ -95,23 +96,25 @@ used by the container and store it inside of the ``WEB_PORT`` variable.
 .. code-block:: bash
 
     # install curl if necessary, then ...
-    curl http://127.0.0.1:$WEB_PORT
-      Hello world!
+    $ curl http://127.0.0.1:$WEB_PORT
+    Hello world!
 
 Access the web app using the ``curl`` binary. If everything worked as planned you
 should see the line ``Hello world!`` inside of your console.
 
-**Video:**
+.. code-block:: bash
 
-See the example in action
+    $ sudo docker ps --all
 
-.. raw:: html
+List ``--all`` the Docker containers. If this container had already finished
+running, it will still be listed here with a status of 'Exit 0'.
 
-   <iframe width="720" height="400" frameborder="0"
-           sandbox="allow-same-origin allow-scripts" 
-   srcdoc="<body><script type=&quot;text/javascript&quot; 
-           src=&quot;https://asciinema.org/a/2573.js&quot; 
-           id=&quot;asciicast-2573&quot; async></script></body>">
-   </iframe>
+.. code-block:: bash
+
+    $ 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.
 
-Continue to :ref:`running_ssh_service`.