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Chapter 12. Using Ruby on Rails
Ruby on Rails is a web framework written in Ruby. This guide covers using Rails 4 on Red Hat OpenShift Service on AWS.
Go through the whole tutorial to have an overview of all the steps necessary to run your application on the Red Hat OpenShift Service on AWS. If you experience a problem try reading through the entire tutorial and then going back to your issue. It can also be useful to review your previous steps to ensure that all the steps were run correctly.
12.1. Prerequisites
- Basic Ruby and Rails knowledge.
- Locally installed version of Ruby 2.0.0+, Rubygems, Bundler.
- Basic Git knowledge.
- Running instance of Red Hat OpenShift Service on AWS 4.
-
Make sure that an instance of Red Hat OpenShift Service on AWS is running and is available. Also make sure that your
oc
CLI client is installed and the command is accessible from your command shell, so you can use it to log in using your email address and password.
12.2. Setting up the database
Rails applications are almost always used with a database. For local development use the PostgreSQL database.
Procedure
Install the database:
$ sudo yum install -y postgresql postgresql-server postgresql-devel
Initialize the database:
$ sudo postgresql-setup initdb
This command creates the
/var/lib/pgsql/data
directory, in which the data is stored.Start the database:
$ sudo systemctl start postgresql.service
When the database is running, create your
rails
user:$ sudo -u postgres createuser -s rails
Note that the user created has no password.
12.3. Writing your application
If you are starting your Rails application from scratch, you must install the Rails gem first. Then you can proceed with writing your application.
Procedure
Install the Rails gem:
$ gem install rails
Example output
Successfully installed rails-4.3.0 1 gem installed
After you install the Rails gem, create a new application with PostgreSQL as your database:
$ rails new rails-app --database=postgresql
Change into your new application directory:
$ cd rails-app
If you already have an application, make sure the
pg
(postgresql) gem is present in yourGemfile
. If not, edit yourGemfile
by adding the gem:gem 'pg'
Generate a new
Gemfile.lock
with all your dependencies:$ bundle install
In addition to using the
postgresql
database with thepg
gem, you also must ensure that theconfig/database.yml
is using thepostgresql
adapter.Make sure you updated
default
section in theconfig/database.yml
file, so it looks like this:default: &default adapter: postgresql encoding: unicode pool: 5 host: localhost username: rails password: <password>
Create your application’s development and test databases:
$ rake db:create
This creates
development
andtest
database in your PostgreSQL server.
12.3.1. Creating a welcome page
Since Rails 4 no longer serves a static public/index.html
page in production, you must create a new root page.
To have a custom welcome page must do following steps:
- Create a controller with an index action.
- Create a view page for the welcome controller index action.
- Create a route that serves applications root page with the created controller and view.
Rails offers a generator that completes all necessary steps for you.
Procedure
Run Rails generator:
$ rails generate controller welcome index
All the necessary files are created.
edit line 2 in
config/routes.rb
file as follows:root 'welcome#index'
Run the rails server to verify the page is available:
$ rails server
You should see your page by visiting http://localhost:3000 in your browser. If you do not see the page, check the logs that are output to your server to debug.
12.3.2. Configuring application for Red Hat OpenShift Service on AWS
To have your application communicate with the PostgreSQL database service running in Red Hat OpenShift Service on AWS you must edit the default
section in your config/database.yml
to use environment variables, which you must define later, upon the database service creation.
Procedure
Edit the
default
section in yourconfig/database.yml
with pre-defined variables as follows:Sample
config/database
YAML file<% user = ENV.key?("POSTGRESQL_ADMIN_PASSWORD") ? "root" : ENV["POSTGRESQL_USER"] %> <% password = ENV.key?("POSTGRESQL_ADMIN_PASSWORD") ? ENV["POSTGRESQL_ADMIN_PASSWORD"] : ENV["POSTGRESQL_PASSWORD"] %> <% db_service = ENV.fetch("DATABASE_SERVICE_NAME","").upcase %> default: &default adapter: postgresql encoding: unicode # For details on connection pooling, see rails configuration guide # http://guides.rubyonrails.org/configuring.html#database-pooling pool: <%= ENV["POSTGRESQL_MAX_CONNECTIONS"] || 5 %> username: <%= user %> password: <%= password %> host: <%= ENV["#{db_service}_SERVICE_HOST"] %> port: <%= ENV["#{db_service}_SERVICE_PORT"] %> database: <%= ENV["POSTGRESQL_DATABASE"] %>
12.3.3. Storing your application in Git
Building an application in Red Hat OpenShift Service on AWS usually requires that the source code be stored in a git repository, so you must install git
if you do not already have it.
Prerequisites
- Install git.
Procedure
Make sure you are in your Rails application directory by running the
ls -1
command. The output of the command should look like:$ ls -1
Example output
app bin config config.ru db Gemfile Gemfile.lock lib log public Rakefile README.rdoc test tmp vendor
Run the following commands in your Rails app directory to initialize and commit your code to git:
$ git init
$ git add .
$ git commit -m "initial commit"
After your application is committed you must push it to a remote repository. GitHub account, in which you create a new repository.
Set the remote that points to your
git
repository:$ git remote add origin git@github.com:<namespace/repository-name>.git
Push your application to your remote git repository.
$ git push
12.4. Deploying your application to Red Hat OpenShift Service on AWS
You can deploy you application to Red Hat OpenShift Service on AWS.
After creating the rails-app
project, you are automatically switched to the new project namespace.
Deploying your application in Red Hat OpenShift Service on AWS involves three steps:
- Creating a database service from Red Hat OpenShift Service on AWS’s PostgreSQL image.
- Creating a frontend service from Red Hat OpenShift Service on AWS’s Ruby 2.0 builder image and your Ruby on Rails source code, which are wired with the database service.
- Creating a route for your application.
12.4.1. Creating the database service
Procedure
Your Rails application expects a running database service. For this service use PostgreSQL database image.
To create the database service, use the oc new-app
command. To this command you must pass some necessary environment variables which are used inside the database container. These environment variables are required to set the username, password, and name of the database. You can change the values of these environment variables to anything you would like. The variables are as follows:
- POSTGRESQL_DATABASE
- POSTGRESQL_USER
- POSTGRESQL_PASSWORD
Setting these variables ensures:
- A database exists with the specified name.
- A user exists with the specified name.
- The user can access the specified database with the specified password.
Procedure
Create the database service:
$ oc new-app postgresql -e POSTGRESQL_DATABASE=db_name -e POSTGRESQL_USER=username -e POSTGRESQL_PASSWORD=password
To also set the password for the database administrator, append to the previous command with:
-e POSTGRESQL_ADMIN_PASSWORD=admin_pw
Watch the progress:
$ oc get pods --watch
12.4.2. Creating the frontend service
To bring your application to Red Hat OpenShift Service on AWS, you must specify a repository in which your application lives.
Procedure
Create the frontend service and specify database related environment variables that were setup when creating the database service:
$ oc new-app path/to/source/code --name=rails-app -e POSTGRESQL_USER=username -e POSTGRESQL_PASSWORD=password -e POSTGRESQL_DATABASE=db_name -e DATABASE_SERVICE_NAME=postgresql
With this command, Red Hat OpenShift Service on AWS fetches the source code, sets up the builder, builds your application image, and deploys the newly created image together with the specified environment variables. The application is named
rails-app
.Verify the environment variables have been added by viewing the JSON document of the
rails-app
deployment config:$ oc get dc rails-app -o json
You should see the following section:
Example output
env": [ { "name": "POSTGRESQL_USER", "value": "username" }, { "name": "POSTGRESQL_PASSWORD", "value": "password" }, { "name": "POSTGRESQL_DATABASE", "value": "db_name" }, { "name": "DATABASE_SERVICE_NAME", "value": "postgresql" } ],
Check the build process:
$ oc logs -f build/rails-app-1
After the build is complete, look at the running pods in Red Hat OpenShift Service on AWS:
$ oc get pods
You should see a line starting with
myapp-<number>-<hash>
, and that is your application running in Red Hat OpenShift Service on AWS.Before your application is functional, you must initialize the database by running the database migration script. There are two ways you can do this:
Manually from the running frontend container:
Exec into frontend container with
rsh
command:$ oc rsh <frontend_pod_id>
Run the migration from inside the container:
$ RAILS_ENV=production bundle exec rake db:migrate
If you are running your Rails application in a
development
ortest
environment you do not have to specify theRAILS_ENV
environment variable.
- By adding pre-deployment lifecycle hooks in your template.
12.4.3. Creating a route for your application
You can expose a service to create a route for your application.