OpenShift is a PaaS that allow you to run your own app for free with low resources. It offers 1GB storage and 512MB RAM, and has support for custom domains. It's faster than Heroku, PagodaBox, and AppFog giving you SSH access to your app server, running in a separate environment. It's just like a real server, but you get it for free.

OpenShift is a very good platform for running a WordPress site. PagodaBox and AppFog fair for hosting PHP applications for free; however, PagodaBox is quite slow, and has a hard limit of 10MB of MySQL for free plan. AppFog no longer supports custom domain on their free plan. You can also run PHP on Heroku, but it's a bit on the slow, as well. 

OpenShift solve all of above problems: It's fast enough, offers a free custom domain, offers large disk space, and a significant amount of MySQL storage. 

The free plan supports:

1. 15 pages/second
2. ~50k visitors per month
   

That's a good amount for most of personal blog. Accordingly to OpenShift documentation:

OpenShift is a next-generation cloud application platform that makes it easy to develop, deploy, and scale applications in the cloud – public or private.

Let's break it down.

• Ease of Development: Quickly create an app environment with many language and run time libraries from the website UI or command line.  OpenShift supports a free, private Git repository meaning you don't even have to pay for your own Git server or a private plan on GitHub. You will use this repository for deployment (we will learn later), don't deploy via uploading file directly. This repository is important and you will use it throught development to deployment.
  
• Ease of Deployment: Whenever you push to your Git repository, OpenShift will pickup the changes and deploy it for you. By default, it deploys code from the master branch, but you can change to whatever branches/tags if you want. You no longer need to use an FTP client or to build your custom deployment method. All are done by OpenShift with a simple git push to the repository which OpenShift created for you.
  
• Scalable: When you have more traffic, you can easily add more gears, like you add more server to your app.
  

Your app, to OpenShift point of view contains:

1. Your code
2. Git repository
3. Environment variables
4. App environment

The git repository is created and maintained by OpenShift itself, too. You must push to it to trigger deployment.

Your app runs on a set of cartridges. A cartridge, by OpenShift's definition, are self-contained pieces of the application stack such as the web server and the database server. These cartridges are deployed and run on one or more secure containers call gears. 

So, for a PHP application, you can have a MySQL server, a web server, a Memcache server, a logging server, and a Gearman worker. All of these are cartridges. Gears are what will run these cartridges. You can think of a gear like a separate virtual server, and cartridge is the technology stack; therefore, to scale your app, you can add more gears into it. 

To expand your technology stack, you add more cartridges, like adding a RabbitMQ. Gears shared configuration information with your app via environment variables. For example, you won't directly write down a MySQL username or MySQL password in a config file. Instead, you would use getenv to load environment variables. If you hard code the configuration, when you deploy on new gear, it stops working. 

define('DB_NAME', getenv('OPENSHIFT_APP_NAME'));

/** MySQL database username */
define('DB_USER', getenv('OPENSHIFT_MYSQL_DB_USERNAME'));

/** MySQL database password */
define('DB_PASSWORD', getenv('OPENSHIFT_MYSQL_DB_PASSWORD'));

/** MySQL hostname */
define('DB_HOST', getenv('OPENSHIFT_MYSQL_DB_HOST') . ':' . getenv('OPENSHIFT_MYSQL_DB_PORT'));

Sharing configuration via environment is the way multiple gears can know each others information. If you are convinced, let's continue.

Step 1: Sign Up for an Account

Go to here and sign up for an account. You only need to signup for a free account. Skip if you has already had an account there.

Step 2: Setup Your Publish Key

You will need a public key for connection between you and  OpenShift later. A public key is  a plain text file usually name id_rsa.pub that's located in ~/.ssh/. 

So if you are on a Mac, it's in /Users/[your_username]/.ssh/id_rsa.pub or if you are on Linux it's in /home/[your_user_name]/.ssh/id_rsa.pub. You need to copy content of this file and update it with OpenShift so OpenShift is aware of your public key. When you make a connection to OpenShift from the terminal (that is, when you SSH to your box and are pushing code), OpenShift will identify and authorize you by based on your public/private key.

If you are not familiar with the public key concept, this tutorial will give you a solid background for it.

To check if you have had a public key before, run this command:

ls -la ~/.ssh | grep id_rsa.pub

If you get this result:

id_rsa.pub

then you already have a public key. If the above command returns nothing, then you don't have one. 

Let's generate it with command:

$ ssh-keygen -t rsa

You can just use the default option when it asks you. Once you're done, you can confirm that you have that file by running ls -la ~/.ssh | grep id_rsa.pub again. An according private key file are also generate under name ~/.ssh/id_rsa(not .pub extension) for you. We will use it later, too.

Now, login to OpenShift, go to the Setting tab. You have to set up a name space for all your app. Later on OpenShift give you the sub domain in this format: http://applicationname–[your_name_space].rhcloud.com. For example, I use tutsplus as name space here. Now, let's copy content of public key into clipboard.

If you are on Mac, you can use this command to copy content into a file quickly:

$ cat ~/.ssh/id_rsa.pub| pbcopy

If you are on Linux, just run this command: cat ~/.ssh/id_rsa.pub, then manually copy the output.

Step 2: Get Your WordPress Up

To get WordPress up and running, you can start from scratch with the OpenShift command line tools, or you can use the GUI to create it. Using a GUI can be easier for starting so let's use it. We will dive more into CLI mode later.

Step 2A: A Fresh Installation

Login to OpenShift and do the following:

1. Select the tab "Application". 
2. Click "Create your first application now"
3. Type "WordPress" into "Search by keyword or tag" input field to filter WordPress.
4. Click on "WordPress 3.x". This will give us a WordPress 3.8.x version.

Now, you will be redirect to a screen for entering your blog information.

• Public URL: Set your blog URL. This is a sub domain under rhcloud.com. You can select any name because we will change it with its own domain later anyway. In this tutorial I will use http://demo2-tutsplus.rhcloud.com. Tutsplus is my name space and demo2 is name of my app.
  
• Cartridge: Let's choose PHP5.4 and MySQL 5.5.
• Leave other field defaults.
• Click "Create application"

Wait for a few moments and your application will be created. Next, you will be presented with a page that contains:

1. MySQL credential. Store it, you will need it later.
   
2. Git repository address of your WordPress instance on OpenShift platform.
   

Let's clone this repository to our local machine. For example my own one look like this

git clone ssh://[email protected]/~/git/php.git/

We will come back this later. Click "Continue to the application overview page" and your app will be appear with the domain that you choose. Launch it on your browser and you can proceed with normal WordPress installation: Setting up the site name, admin username, and the admin password just as you're used to doing with WordPress.

The next step is for people who already have WordPress installed somewhere and want to move to OpenShift. If you are doing a fresh install, you can ignore this, but I suggest you to read it for some additional understanding of the OpenShift structure.

Step 2B: An Existing Installation

If you have existing WordPress code, it's not so hard to implement on top of OpenShift. You have several options:

1. Export current data, create a new WordPress installation, on OpenShift and just import it.
2. Check in your code to the repository we cloned in previous step and tweak wp-config.php to match OpenShift's requirements.

Here's some additional detail about the second step as the migration includes three things:

1. Code integration such as your themes and/or plugins.
   
2. Database Migration. In later step, you will learn to configure phpMyAdmin on OpenShift so you can backup current WordPress data with phpMyAdmin then import to OpenShift via its phpMyAdmin. Just make sure you use same phpMyAdmin version to minimize compatibility issues.
   
3. Media Migration. In later step, you will learn about SSH/SFTP access. Once you have SSH you can simply copy all media files in wp-content/uploads to OpenShift.
   

In this step, I'm only covering code integration. In a previous step, we cloned WordPress repository with:

git clone ssh://[email protected]/~/git/php.git/

You should have a layout like this inside the repository. Make sure to display hidden files, as well:

The beautiful thing about OpenShift is that it has a good structure for WordPress. When working on WordPress, you only worry about wp-config.php, plugins, and themes. That's it. 

The other files, or WordPress core file (wp-admin, wp-includes, wp-content/uploads, index.php, wp-login.php...) are handled by OpenShift. OpenShift will automatically pull the files from WordPress and put it into the correct location for you.

.openshift folder is where most of your code will reside. plugins and themes are corresponding folders for WordPress. config/wp-config.php is your custom WordPress config file.

.openshift/action_hooks contains build and deploy related scripts. Those scripts are what will be run on OpenShift server to deploy your app. If you want to custom the build process, you have to configure those script files.

Here is a part of the deployment workflow whenever a push to the deploy branch (usually this is the master) is triggered from Git:

1. OpenShift creates a folder which we'll call install_dir. Next, download and extract the file http://wordpress.org/wordpress-${install_version}.tar.gz into this folder. The install_version is pre-defined in .openshift/action_hooks/build
2. OpenShift copies the file .openshift/config/wp-config.php to overwrite the file in install_dir/wp-config.php (the default wp-config.php from original package
3. OpenShift copy all content of .openshift/plugins and .openshift/themes to install_dir/wp-content/plugins and install_dir/wp-content/themes

So,  to migrate a current WordPress file to OpenShift, you copy all your current WordPress themes and plugins to folder .openshift/plugins or .openshift/themes accordingly.  Then commit your code and push everything back to OpenShift. 

For example:

$ cd your_current_wordpress
# We will recursive copy all file/folder under wp-content/uploads to  
$ scp -r wp-content/uploads/* [email protected]:~/app-root/data/current/wp-content/uploads

Make sure to use correct username and server name. It's very important that you use correct username, otherwise you won't be able to connect.

SFTP Connecting to Your App

OpenShift doesn't support FTP but you can use SSH File Transfer Protocol to get access and browser the file system; however, don't use this method to upload and edit file directly. 

Consider this as a way to help you view the file structure on your app quickly if you are not familiar with command line. We'll use FileZilla to connect. We won't use password authentication but public/private key authentication. We already setup the public key before. Now, let add a new server as in screen. Change it to your setting.

Save it. Next, we need to update our private key with FileZilla because we won't use password authentication on OpenShift. Open FileZilla Preference, Select SFTP->Add Key File then chose your private key that we generated together with public key in previous step. It should be in /Users/yourname/.ssh/id_rsa. 

Note that since .ssh include a dot, Mac will hide it, so you can follow these tips to show hidden file in Mac.

Answer yes when it asks for converting. Now, you can connect to the host we saved before. 

Once you are in, you can navigate around and have a sense of folder layout. But make sure you don't manually remove delete WordPress code there a the right way for OpenShift deployment is to use its Git repository. You still can manually upload file, but you will lose other nice feature of OpenShift deployment.

Using a GUI can be easy to see things comparing to use SSH on terminal but don't abuse this SFTP method, we should consider it as a quick way to verify if some files are there, not to use it for deployment. But you can use it to download (for backup purpose) media data in app-root/data/uploads.