Ruby on rails with multiple production settings

How can we run a ruby on rails application with different database configuration?

in de开发者_JAVA技巧tail: I want to run multiple instance of a rails app with different database config for each on production. How is it possible?

I think you can duplicate the config in database.yml into different environments, like prod1, prod2 ... and then set RAILS_ENV environment variable to match before starting up each respective server...

You can duplicate your database.yml file as DGM mentioned. However, the right way to do this would be to use a configuration management solution like Chef.

If you look at the guide for setting up Rails stack, it includes a 2 front-end Web server + 1 back-end DB server. Which would include your case of duplicating database.yml file.

If you are able to control and configure each Rails instance, and you can afford wasting resources because of them being on standby, save yourself some trouble and just change the database.yml to modify the database connection used on every instance. If you are concerned about performance this approach won't cut it.

For models bound to a single unique table on only one database you can call establish_connection inside the model:

establish_connection "database_name_#{RAILS_ENV}"

As described here: http://apidock.com/rails/ActiveRecord/Base/establish_connection/class

You will have some models using tables from one database and other different models using tables from other databases.

If you have identical tables, common on different databases, and shared by a single model, ActiveRecord won't help you. Back in 2009 I required this on a project I was working on, using Rails 2.3.8. I had a database for each customer, and I named the databases with their IDs. So I created a method to change the connection inside ApplicationController:

def change_database database_id = params[:company_id]
    return if database_id.blank?

    configuration = ActiveRecord::Base.connection.instance_eval { @config }.clone
    configuration[:database] = "database_name_#{database_id}_#{RAILS_ENV}"

    MultipleDatabaseModel.establish_connection configuration
end

And added that method as a *before_filter* to all controllers:

before_filter :change_database

So for each action of each controller, when params[:company_id] is defined and set, it will change the database to the correct one.

To handle migrations I extended ActiveRecord::Migration, with a method that looks for all the customers and iterates a block with each ID:

class ActiveRecord::Migration
    def self.using_databases *args
        configuration = ActiveRecord::Base.connection.instance_eval { @config }
        former_database = configuration[:database]

        companies = args.blank? ? Company.all : Company.find(args)

        companies.each do |company|
            configuration[:database] = "database_name_#{company[:id]}_#{RAILS_ENV}"
            ActiveRecord::Base.establish_connection configuration

            yield self
        end

        configuration[:database] = former_database
        ActiveRecord::Base.establish_connection configuration
    end
end

Note that by doing this, it would be impossible for you to make queries within the same action from two different databases. You can call *change_database* again but it will get nasty when you try using methods that execute queries, from the objects no longer linked to the correct database. Also, it is obvious you won't be able to join tables that belong to different databases.

To handle this properly, ActiveRecord should be considerably extended. There should be a plugin by now to help you with this issue. A quick research gave me this one:

DB-Charmer: http://kovyrin.github.com/db-charmer/

I'm willing to try it. Let me know what works for you.

Well. We have to create multiple environments in you application

create config/environmenmts/production1.rb which will be same as of config/environmenmts/production.rb

then edit database.yml for production1 settings and you are done.

start server using rails s -e production1