Rack::ErrorToSlack
This is a rack middleware that post error to slack.
EXAMPLE: 
Installation
Add this line to your application's Gemfile:
gem 'rack-error_to_slack'
And then execute:
$ bundle install
Or install it yourself as:
$ gem install rack-error_to_slack
Usage
for Rails 4.x
Step1
config/environments/development.rb
config.middleware.use Rack::ErrorToSlack
Step2
config/initializers/error_to_slack.rb
Rack::ErrorToSlack.configure do |config|
config.webhook_url = 'https://hooks.slack.com/services/your_webhook_url'
### follows are option ###
# emoji icon of slack post
config.emoji = ':ghost:' # default: ':innocent:'
# username of slack post
config.slackname = 'ErrorSharing' # default: 'ErrorToSlack'
end