Chapter 7. Application Tutorials

Rails applications are almost always used with a database. For the local development we chose the PostgreSQL database. To install it type:

$ sudo yum install -y postgresql postgresql-server postgresql-devel

Next you need to initialize the database with:

$ sudo postgresql-setup initdb

This command will create the /var/lib/pgsql/data directory, in which the data will be stored.

Start the database by typing:

$ sudo systemctl start postgresql.service

When the database is running, create your rails user:

$ sudo -u postgres createuser -s rails

Note that the user we created has no password.

Since Rails 4 no longer serves a static public/index.html page in production, we need to create a new root page.

In order to have a custom welcome page we need to do following steps:

Rails offers a generator that will do all this necessary steps for you.

$ rails generate controller welcome index

All the necessary files have been created, now we just need to edit line 2 in config/routes.rb file to look like:

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 don’t see the page, check the logs that are output to your server to debug.

In order to have your application communicating with the PostgreSQL database service that will be running in OpenShift Container Platform, you will need to edit the default section in your config/database.yml to use environment variables, which you will define later, upon the database service creation.

The default section in your edited config/database.yml together with pre-defined variables should look like:

<% 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"] %>

For an example of how the final file should look, see Ruby on Rails example application config/database.yml.

OpenShift Container Platform requires git, if you don’t have it installed you will need to install it.

Building an application in OpenShift Container Platform usually requires that the source code be stored in a git repository, so you will need to install git if you do not already have it.

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
app
bin
config
config.ru
db
Gemfile
Gemfile.lock
lib
log
public
Rakefile
README.rdoc
test
tmp
vendor

Now run these commands in your Rails app directory to initialize and commit your code to git:

$ git init
$ git add .
$ git commit -m "initial commit"

Once your application is committed you need to push it to a remote repository. For this you would need a 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

After that, push your application to your remote git repository.

$ git push

Your Rails application expects a running database service. For this service use PostgeSQL database image.

To create the database service you will use the oc new-app command. To this command you will need to pass some necessary environment variables which will be 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 we are going to be setting are as follows:

Setting these variables ensures:

For example:

$ 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

To watch the progress of this command:

$ oc get pods --watch

To bring your application to OpenShift Container Platform, you need to specify a repository in which your application lives, using once again the oc new-app command, in which you will need to specify database related environment variables we setup in the 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, OpenShift Container Platform fetches the source code, sets up the builder image, builds your application image, and deploys the newly created image together with the specified environment variables. The application is named rails-app.

You can verify the environment variables have been added by viewing the JSON document of the rails-app DeploymentConfig:

$ oc get dc rails-app -o json

You should see the following section:

env": [
    {
        "name": "POSTGRESQL_USER",
        "value": "username"
    },
    {
        "name": "POSTGRESQL_PASSWORD",
        "value": "password"
    },
    {
        "name": "POSTGRESQL_DATABASE",
        "value": "db_name"
    },
    {
        "name": "DATABASE_SERVICE_NAME",
        "value": "postgresql"
    }

],

To check the build process:

$ oc logs -f build rails-app-1

Once the build is complete, you can look at the running pods in OpenShift Container Platform.

$ oc get pods

You should see a line starting with myapp-<number>-<hash>, and that is your application running in OpenShift Container Platform.

Before your application will be functional, you need to initialize the database by running the database migration script. There are two ways you can do this:

First you need to 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 or test environment you don’t have to specify the RAILS_ENV environment variable.

To expose a service by giving it an externally-reachable hostname like www.example.com use OpenShift Container Platform route. In your case you need to expose the frontend service by typing:

$ oc expose service rails-app --hostname=www.example.com

This is a good time to set up readiness and liveness probes. These will periodically check to see that Nexus is running properly.

$ oc set probe dc/nexus \
	--liveness \
	--failure-threshold 3 \
	--initial-delay-seconds 30 \
	-- echo ok
$ oc set probe dc/nexus \
	--readiness \
	--failure-threshold 3 \
	--initial-delay-seconds 30 \
	--get-url=http://:8081/nexus/content/groups/public

Create a persistent volume claim (PVC) for Nexus, so that the cached dependencies are not lost when the pod running the server terminates. PVCs require available persistent volumes (PV) in the cluster. If there are no PVs available and you do not have administrator access on your cluster, ask your system administrator to create a Read/Write Persistent Volume for you. Otherwise, see Persistent Storage in OpenShift Container Platform for instructions on creating a persistent volume.

Add a PVC to the Nexus deployment configuration.

$ oc volumes dc/nexus --add \
	--name 'nexus-volume-1' \
	--type 'pvc' \
	--mount-path '/sonatype-work/' \
	--claim-name 'nexus-pv' \
	--claim-size '1G' \
	--overwrite

This removes the previous emptyDir volume for the deployment config and adds a claim for one gigabyte of persistent storage mounted at /sonatype-work, which is where the dependencies will be stored. Due to the change in configuration, the Nexus pod will be redeployed automatically.

To verify that Nexus is running, refresh the Nexus page in your browser. You can monitor the deployment’s progress using:

$ oc get pods -w