Aaron Kromer's Blog

Recently at work, we’ve been spinning up a bunch of demo apps on Heroku. This has worked out well for us so far. However, some of these apps require background data crunching. This hasn’t been a problem as we just add a Rake task, or two, and set the Heroku scheduler to take care of things.

Then comes the day when the sales team says:

“Oh hey. Can we re-run all the numbers but with different configurations?”

Sure, that’s not a problem you think:

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$ heroku run rake redo_all_the_things[config.yml]

However, there’s a few issues with this:

1. The config.yml needs to be on Heroku
2. This counts against your active dyno time

See the thing is, Heroku doesn’t let you create files that aren’t already in your VC system from outside the app. It’s now sorta possible on Cedar, but not really for this purpose.

Additionally, if these tasks turn out to be long running, that’ll quickly eat up the overhead on the ‘free’ dyno. For demo apps of non-paying customers that’s not always an option.

Enter the live environment.

Just add a new live environment to the Rails application. This allows us to run Rake locally, but against the production database. Additionally, allowing for custom configuration files to just be stored on our local system. And we don’t spin up a new dyno on Heroku. Win, win!

To set this up:

• Update the Gemfile

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# Gemfile

# We use dotenv-rails to help manage environment configs locally.
# Add our new environment:
gem 'dotenv-rails', groups: [:development, :test, :live]

• Add the live specific sample file: .env.live-example

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# .env.live-example

# Rename this file to `.env.live` and it will be automatically sourced by
# rails. Uncomment the settings for them to be picked up.
#
# Grab the settings from the output of:
#
#  $ heroku config
#
# Running against the Heroku production DB directly
# BE CAREFUL!! YOU HAVE BEEN WARNED!!
#DATABASE_NAME=WARNING
#DATABASE_HOST=DANGER
#DATABASE_PORT=WILL
#DATABASE_USER=ROBINSON
#DATABASE_PASSWORD=SERIOUSLY

• Update the database.yml file

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# config/database.yml

live:
  adapter: postgresql
  encoding: unicode
  database: <%= ENV['DATABASE_NAME'] %>
  host: <%= ENV['DATABASE_HOST'] %>
  port: <%= ENV['DATABASE_PORT'] %>
  username: <%= ENV['DATABASE_USER'] %>
  password: <%= ENV['DATABASE_PASSWORD'] %>

• Copy config/environments/production.rb to config/environments/live.rb. If you wish to symlink it instead be wary of how git treats that.

Now running our tasks is as simple as:

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$ RAILS_ENV=live rake redo_all_the_things[config-fun-edition.yml]