Redis config and initialization for rails

redis.rb

#config/initializers/redis.rb
require 'redis'
require 'redis/objects'

REDIS_CONFIG = YAML.load( File.open( Rails.root.join("config/redis.yml") ) ).symbolize_keys
dflt = REDIS_CONFIG[:default].symbolize_keys
cnfg = dflt.merge(REDIS_CONFIG[Rails.env.to_sym].symbolize_keys) if REDIS_CONFIG[Rails.env.to_sym]

$redis = Redis.new(cnfg)
Redis::Objects.redis = $redis
#$redis_ns = Redis::Namespace.new(cnfg[:namespace], :redis => $redis) if cnfg[:namespace]

# To clear out the db before each test
$redis.flushdb if Rails.env = "test"

redis.yml

#config/redis.yml
default:
  host: localhost
  port: 6379
development:
  db: 0
#  namespace: appname_dev
test:
  db: 1
#  namespace: appname_test
production:
  db: 2
  host: 192.168.1.100
#  namespace: appname_prod

Modified @coconup's example:

# config/redis.yml

default: &default
  url: redis://localhost:6379
  db: 0

development:
  <<: *default

test:
  <<: *default

production:
  <<: *default
  url: redis://somehost:6379

# lib/redis.rb

$redis = Redis.new(Rails.application.config_for(:redis))

# config/initializers/redis.rb
# You can probably move this to the autoload_paths in your regular config/application.rb

Rails.application.config.autoload_paths += Dir[File.join(Rails.root, "lib", "redis.rb")].each {|l| require l }

Usage:

$ $redis.set("foo", "bar")
> "OK"
$ $redis.get("foo")
> "bar"

This is really helpful and here is a reminder.
I got the error when running RSpec:

There was an error while trying to load the gem 'redis'.
Gem Load Error is: uninitialized constant Redis

I fix it by renaming lib/redis.rb to other name, ex: lib/foo.rb
Maybe the file name redis.rb is confused with the gem lib redis.