Exception Notification

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THIS README IS FOR THE MASTER BRANCH AND REFLECTS THE WORK CURRENTLY EXISTING ON THE MASTER BRANCH. IF YOU ARE WISHING TO USE A NON-MASTER BRANCH OF EXCEPTION NOTIFICATION, PLEASE CONSULT THAT BRANCH'S README AND NOT THIS ONE.

The Exception Notification gem provides a set of notifiers for sending notifications when errors occur in a Rack/Rails application. The built-in notifiers can deliver notifications by email, HipChat, Slack, Mattermost, Teams, IRC, Amazon SNS, Google Chat, Datadog or via custom WebHooks.

There's a great Railscast about Exception Notification you can see that may help you getting started.

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Requirements

  • Ruby 2.5 or greater
  • Rails 5.2 or greater, Sinatra or another Rack-based application.

Getting Started

Add the following line to your application's Gemfile:

gem 'exception_notification'

Rails

ExceptionNotification is used as a rack middleware, or in the environment you want it to run. In most cases you would want ExceptionNotification to run on production. Thus, you can make it work by putting the following lines in your config/environments/production.rb:

Rails.application.config.middleware.use ExceptionNotification::Rack,
  email: {
    email_prefix: '[PREFIX] ',
    sender_address: %{"notifier" <[email protected]>},
    exception_recipients: %w{[email protected]}
  }

Note: In order to enable delivery notifications by email make sure you have ActionMailer configured.

Rack/Sinatra

In order to use ExceptionNotification with Sinatra, please take a look in the example application.

Custom Data, e.g. Current User

Save the current user in the request using a controller callback.

class ApplicationController < ActionController::Base
  before_action :prepare_exception_notifier

  private

  def prepare_exception_notifier
    request.env["exception_notifier.exception_data"] = {
      current_user: current_user
    }
  end
end

The current user will show up in your email, in a new section titled "Data".

------------------------------- Data:

* data: {:current_user=>
  #<User:0x007ff03c0e5860
   id: 3,
   email: "[email protected]", # etc...

For more control over the display of custom data, see "Email notifier -> Options -> sections" below.

Notifiers

ExceptionNotification relies on notifiers to deliver notifications when errors occur in your applications. By default, 8 notifiers are available:

But, you also can easily implement your own custom notifier.

Error Grouping

In general, ExceptionNotification will send a notification when every error occurs, which may result in a problem: if your site has a high throughput and a particular error is raised frequently, you will receive too many notifications. During a short period of time, your mail box may be filled with thousands of exception mails, or your mail server may even become slow. To prevent this, you can choose to group errors by setting the :error_grouping option to true.

Error grouping uses a default formula of log2(errors_count) to determine whether to send the notification, based on the accumulated error count for each specific exception. This makes the notifier only send a notification when the count is: 1, 2, 4, 8, 16, 32, 64, 128, ..., (2**n). You can use :notification_trigger to override this default formula.

The following code shows the available options to configure error grouping:

Rails.application.config.middleware.use ExceptionNotification::Rack,
  ignore_exceptions: ['ActionView::TemplateError'] + ExceptionNotifier.ignored_exceptions,
  email:  {
    email_prefix: '[PREFIX] ',
    sender_address: %{"notifier" <[email protected]>},
    exception_recipients: %w{[email protected]}
  },
  error_grouping: true,
  # error_grouping_period: 5.minutes,    # the time before an error is regarded as fixed
  # error_grouping_cache: Rails.cache,   # for other applications such as Sinatra, use one instance of ActiveSupport::Cache::Store
  #
  # notification_trigger: specify a callback to determine when a notification should be sent,
  #   the callback will be invoked with two arguments:
  #     exception: the exception raised
  #     count: accumulated errors count for this exception
  #
  # notification_trigger: lambda { |exception, count| count % 10 == 0 }

Ignore Exceptions

You can choose to ignore certain exceptions, which will make ExceptionNotification avoid sending notifications for those specified. There are three ways of specifying which exceptions to ignore:

  • :ignore_exceptions - By exception class (i.e. ignore RecordNotFound ones)

  • :ignore_crawlers - From crawler (i.e. ignore ones originated by Googlebot)

  • :ignore_if - Custom (i.e. ignore exceptions that satisfy some condition)

  • :ignore_notifer_if - Custom (i.e. let each notifier ignore exceptions if by-notifier condition is satisfied)

:ignore_exceptions

Array of strings, default: %wMongoid::Errors::DocumentNotFound AbstractController::ActionNotFound ActionController::RoutingError ActionController::UnknownFormat

Ignore specified exception types. To achieve that, you should use the :ignore_exceptions option, like this:

Rails.application.config.middleware.use ExceptionNotification::Rack,
                                        ignore_exceptions: ['ActionView::TemplateError'] + ExceptionNotifier.ignored_exceptions,
                                        email: {
                                          email_prefix: '[PREFIX] ',
                                          sender_address: %{"notifier" <[email protected]>},
                                          exception_recipients: %w{[email protected]}
                                        }

The above will make ExceptionNotifier ignore a TemplateError exception, plus the ones ignored by default.

:ignore_crawlers

Array of strings, default: []

In some cases you may want to avoid getting notifications from exceptions made by crawlers. To prevent sending those unwanted notifications, use the :ignore_crawlers option like this:

Rails.application.config.middleware.use ExceptionNotification::Rack,
                                        ignore_crawlers: %w{Googlebot bingbot},
                                        email: {
                                          email_prefix: '[PREFIX] ',
                                          sender_address: %{"notifier" <[email protected]>},
                                          exception_recipients: %w{[email protected]}
                                        }

:ignore_if

Lambda, default: nil

You can ignore exceptions based on a condition. Take a look:

Rails.application.config.middleware.use ExceptionNotification::Rack,
                                        ignore_if: ->(env, exception) { exception.message =~ /^Couldn't find Page with ID=/ },
                                        email: {
                                          email_prefix: '[PREFIX] ',
                                          sender_address: %{"notifier" <[email protected]>},
                                          exception_recipients: %w{[email protected]},
                                        }

You can make use of both the environment and the exception inside the lambda to decide wether to avoid or not sending the notification.

:ignore_notifier_if

  • Hash of Lambda, default: nil*

In case you want a notifier to ignore certain exceptions, but don't want other notifiers to skip them, you can set by-notifier ignore options. By setting below, each notifier will ignore exceptions when its corresponding condition is met.

Rails.application.config.middleware.use ExceptionNotification::Rack,
                                        ignore_notifier_if: {
                                          email: ->(env, exception) { !Rails.env.production? },
                                          slack: ->(env, exception) { exception.message =~ /^Couldn't find Page with ID=/ }
                                        }

                                        email: {
                                          sender_address: %{"notifier" <[email protected]>},
                                          exception_recipients: %w{[email protected]}
                                        },
                                        slack: {
                                          webhook_url: '[Your webhook url]',
                                          channel: '#exceptions',
                                        }

To customize each condition, you can make use of environment and the exception object inside the lambda.

Rack X-Cascade Header

Some rack apps (Rails in particular) utilize the "X-Cascade" header to pass the request-handling responsibility to the next middleware in the stack.

Rails' routing middleware uses this strategy, rather than raising an exception, to handle routing errors (e.g. 404s); to be notified whenever a 404 occurs, set this option to "false."

:ignore_cascade_pass

Boolean, default: true

Set to false to trigger notifications when another rack middleware sets the "X-Cascade" header to "pass."

Background Notifications

If you want to send notifications from a background process like DelayedJob, you should use the notify_exception method like this:

begin
  some code...
rescue => e
  ExceptionNotifier.notify_exception(e)
end

You can include information about the background process that created the error by including a data parameter:

begin
  some code...
rescue => e
  ExceptionNotifier.notify_exception(
    e,
    data: { worker: worker.to_s, queue: queue, payload: payload}
  )
end

Manually notify of exception

If your controller action manually handles an error, the notifier will never be run. To manually notify of an error you can do something like the following:

rescue_from Exception, with: :server_error

def server_error(exception)
  # Whatever code that handles the exception

  ExceptionNotifier.notify_exception(
    exception,
    env: request.env, data: { message: 'was doing something wrong' }
  )
end

Extras

Rails

Since his first version, ExceptionNotification was just a simple rack middleware. But, the version 4.0.0 introduced the option to use it as a Rails engine. In order to use ExceptionNotification as an engine, just run the following command from the terminal:

rails g exception_notification:install

This command generates an initialize file (config/initializers/exception_notification.rb) where you can customize your configurations.

Make sure the gem is not listed solely under the production group, since this initializer will be loaded regardless of environment.

Resque/Sidekiq

Instead of manually calling background notifications foreach job/worker, you can configure ExceptionNotification to do this automatically. For this, run:

rails g exception_notification:install --resque

or

rails g exception_notification:install --sidekiq

As above, make sure the gem is not listed solely under the production group, since this initializer will be loaded regardless of environment.

Support and tickets

Here's the list of issues we're currently working on.

To contribute, please read first the Contributing Guide.

Code of Conduct

Everyone interacting in this project's codebases, issue trackers, chat rooms, and mailing lists is expected to follow our code of conduct.

License

Copyright (c) 2005 Jamis Buck, released under the MIT license.