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:title: Running a Node.js app on CentOS
:description: Installing and running a Node.js app on CentOS
:keywords: docker, example, package installation, node, centos
.. _nodejs_web_app:
Node.js Web App
===============
.. include:: example_header.inc
The goal of this example is to show you how you can build your own
Docker images from a parent image using a ``Dockerfile`` . We will do
that by making a simple Node.js hello world web application running on
CentOS. You can get the full source code at
https://github.com/gasi/docker-node-hello.
Create Node.js app
++++++++++++++++++
First, create a directory ``src`` where all the files would live. Then create a ``package.json`` file that describes your app and its
dependencies:
.. code-block:: json
{
"name": "docker-centos-hello",
"private": true,
"version": "0.0.1",
"description": "Node.js Hello World app on CentOS using docker",
"author": "Daniel Gasienica <daniel@gasienica.ch>",
"dependencies": {
"express": "3.2.4"
}
}
Then, create an ``index.js`` file that defines a web app using the
`Express.js <http://expressjs.com/>`_ framework:
.. code-block:: javascript
var express = require('express');
// Constants
var PORT = 8080;
// App
var app = express();
app.get('/', function (req, res) {
res.send('Hello World\n');
});
app.listen(PORT);
console.log('Running on http://localhost:' + PORT);
In the next steps, we’ll look at how you can run this app inside a CentOS
container using Docker. First, you’ll need to build a Docker image of your app.
Creating a ``Dockerfile``
+++++++++++++++++++++++++
Create an empty file called ``Dockerfile``:
.. code-block:: bash
touch Dockerfile
Open the ``Dockerfile`` in your favorite text editor and add the following line
that defines the version of Docker the image requires to build
(this example uses Docker 0.3.4):
.. code-block:: bash
# DOCKER-VERSION 0.3.4
Next, define the parent image you want to use to build your own image on top of.
Here, we’ll use `CentOS <https://index.docker.io/_/centos/>`_ (tag: ``6.4``)
available on the `Docker index`_:
.. code-block:: bash
FROM centos:6.4
Since we’re building a Node.js app, you’ll have to install Node.js as well as
npm on your CentOS image. Node.js is required to run your app and npm to install
your app’s dependencies defined in ``package.json``.
To install the right package for CentOS, we’ll use the instructions from the
`Node.js wiki`_:
.. code-block:: bash
# Enable EPEL for Node.js
RUN rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
# Install Node.js and npm
RUN yum install -y npm
To bundle your app’s source code inside the Docker image, use the ``ADD``
instruction:
.. code-block:: bash
# Bundle app source
ADD . /src
Install your app dependencies using the ``npm`` binary:
.. code-block:: bash
# Install app dependencies
RUN cd /src; npm install
Your app binds to port ``8080`` so you’ll use the ``EXPOSE`` instruction
to have it mapped by the ``docker`` daemon:
.. code-block:: bash
EXPOSE 8080
Last but not least, define the command to run your app using ``CMD``
which defines your runtime, i.e. ``node``, and the path to our app,
i.e. ``src/index.js`` (see the step where we added the source to the
container):
.. code-block:: bash
CMD ["node", "/src/index.js"]
Your ``Dockerfile`` should now look like this:
.. code-block:: bash
# DOCKER-VERSION 0.3.4
FROM centos:6.4
# Enable EPEL for Node.js
RUN rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
# Install Node.js and npm
RUN yum install -y npm
# Bundle app source
ADD . /src
# Install app dependencies
RUN cd /src; npm install
EXPOSE 8080
CMD ["node", "/src/index.js"]
Building your image
+++++++++++++++++++
Go to the directory that has your ``Dockerfile`` and run the following
command to build a Docker image. The ``-t`` flag let’s you tag your
image so it’s easier to find later using the ``docker images``
command:
.. code-block:: bash
sudo docker build -t <your username>/centos-node-hello .
Your image will now be listed by Docker:
.. code-block:: bash
sudo docker images
> # Example
> REPOSITORY TAG ID CREATED
> centos 6.4 539c0211cd76 8 weeks ago
> gasi/centos-node-hello latest d64d3505b0d2 2 hours ago
Run the image
+++++++++++++
Running your image with ``-d`` runs the container in detached mode, leaving the
container running in the background. The ``-p`` flag redirects a public port to a private port in the container. Run the image you previously built:
.. code-block:: bash
sudo docker run -p 49160:8080 -d <your username>/centos-node-hello
Print the output of your app:
.. code-block:: bash
# Get container ID
sudo docker ps
# Print app output
sudo docker logs <container id>
> # Example
> Running on http://localhost:8080
Test
++++
To test your app, get the the port of your app that Docker mapped:
.. code-block:: bash
sudo docker ps
> # Example
> ID IMAGE COMMAND ... PORTS
> ecce33b30ebf gasi/centos-node-hello:latest node /src/index.js 49160->8080
In the example above, Docker mapped the ``8080`` port of the container to
``49160``.
Now you can call your app using ``curl`` (install if needed via:
``sudo apt-get install curl``):
.. code-block:: bash
curl -i localhost:49160
> HTTP/1.1 200 OK
> X-Powered-By: Express
> Content-Type: text/html; charset=utf-8
> Content-Length: 12
> Date: Sun, 02 Jun 2013 03:53:22 GMT
> Connection: keep-alive
>
> Hello World
We hope this tutorial helped you get up and running with Node.js and
CentOS on Docker. You can get the full source code at
https://github.com/gasi/docker-node-hello.
Continue to :ref:`running_redis_service`.
.. _Node.js wiki: https://github.com/joyent/node/wiki/Installing-Node.js-via-package-manager#rhelcentosscientific-linux-6
.. _docker index: https://index.docker.io/
|