$ script/rails generate scaffold messages message:string --orm mongo_mapper 

CloudFoundryRailsTutorial::Application.routes.draw do
  resources :messages
  root :to => "messages#index"
end

Set up our credentials so we can talk to Cloud Foundry’s MongoDB
MongoMapper comes with a generator that will create a basic config/mongo.ymlconfiguration file for us.

$ script/rails generate mongo_mapper:config

The file looks like this:

defaults: &defaults
  host: 127.0.0.1
  port: 27017
development:
<<: *defaults
database: myapp_development
test:
<<: *defaults
database: myapp_test
set these environment variables on your prod server
production:
<<: *defaults
database: myapp
username: <%= ENV['MONGO_USERNAME'] %>
password: <%= ENV['MONGO_PASSWORD'] %>

We need to modify this so that it can talk to Cloud Foundry’s infrastructure. When CloudFoundry runs your app, it passes in a bunch of information through an environment variable. We need to pull the host, port, username, and password for MongoDB out of this environment variable. After some modification, the production section of your config/mongo.ymlshould look something like this:

production:
  host: <%= JSON.parse( ENV['VCAP_SERVICES'] )['mongodb-1.8'].first['credentials']['hostname'] rescue 'localhost' %>
  port: <%= JSON.parse( ENV['VCAP_SERVICES'] )['mongodb-1.8'].first['credentials']['port'] rescue 27017 %>
  database:  <%= JSON.parse( ENV['VCAP_SERVICES'] )['mongodb-1.8'].first['credentials']['db'] rescue 'cloud_foundry_mongodb_tutorial' %>
  username: <%= JSON.parse( ENV['VCAP_SERVICES'] )['mongodb-1.8'].first['credentials']['username'] rescue '' %>
  password: <%= JSON.parse( ENV['VCAP_SERVICES'] )['mongodb-1.8'].first['credentials']['password'] rescue '' %>

Note: The “rescue” clauses are so that you can run this app locally. If you don’t include this and you try to run this app outside of cloud foundry, you’ll get an exception because there’s no VCAP_SERVICES environment variable passed into your app.

Push our application to CloudFoundry
Now we’re ready to test things out. If you haven’t already, you should go ahead and install the vmc command line tool. There’s a getting started with VMC guide here. Here’s what it looked like when I deployed my app:

redeye:myapp jsr$ vmc push --runtime ruby19
Would you like to deploy from the current directory? [Yn]: y
Application Name: mongodb-on-cf-demo
Application Deployed URL: 'mongodb-on-cf-demo.cloudfoundry.com'? 
Detected a Rails Application, is this correct? [Yn]: y
Memory Reservation [Default:256M] (64M, 128M, 256M or 512M) 256M
Creating Application: OK
Would you like to bind any services to 'mongodb-on-cf-demo'? [yN]: y
Would you like to use an existing provisioned service [yN]? n
The following system services are available::
1. mysql
2. mongodb
3. redis
Please select one you wish to provision: 2
Specify the name of the service [mongodb-a8a43]: 
Creating Service: OK
Binding Service: OK
Uploading Application:
  Checking for available resources: OK
  Processing resources: OK
  Packing application: OK
  Uploading (5K): OK   
Push Status: OK
Starting Application: OK                                                        
redeye:myapp jsr$

Now you can point your browser to http://mongodb-on-cf-demo.cloudfoundry.com/ and you should see the list of messages!

Congrats! You’ve got your first Rails app up and running on Cloud Foundry and MongoDB!

The code for this mongodb + rails + Cloud Foundry app is up on github

Happy coding and be sure to tell us about all the awesome apps you build on Cloud Foundry!