How can I tell Sentry not to alert certain exceptions? - ruby-on-rails

Question

I have a Rails 5 application using raven-ruby to send exceptions to Sentry which then sends alerts to our Slack.
Raven.configure do |config|
config.dsn = ENV['SENTRY_DSN']
config.environments = %w[ production development ]
config.excluded_exceptions += []
config.async = lambda { |event|
SentryWorker.perform_async(event.to_hash)
}
end
class SentryWorker < ApplicationWorker
sidekiq_options queue: :default
def perform(event)
Raven.send_event(event)
end
end
It's normal for our Sidekiq jobs to throw exceptions and be retried. These are mostly intermittent API errors and timeouts which clear up on their own in a few minutes. Sentry is dutifully sending these false alarms to our Slack.
I've already added the retry_count to the jobs. How can I prevent Sentry from sending exceptions with a retry_count < N to Slack while still alerting for other exceptions? An example that should not be alerted will have extra context like this:
sidekiq: {
context: Job raised exception,
job: {
args: [{...}],
class: SomeWorker,
created_at: 1540590745.3296254,
enqueued_at: 1540607026.4979043,
error_class: HTTP::TimeoutError,
error_message: Timed out after using the allocated 13 seconds,
failed_at: 1540590758.4266324,
jid: b4c7a68c45b7aebcf7c2f577,
queue: default,
retried_at: 1540600397.5804272,
retry: True,
retry_count: 2
},
}
What are the pros and cons of not sending them to Sentry at all vs sending them to Sentry but not being alerted?

Answer 1

Summary
An option that has worked well for me is by configuring Sentry's should_capture alongside Sidekiq's sidekiq_retries_exhausted with a custom attribute on the exception.
Details
1a. Add the custom attribute
You can add a custom attribute to an exception. You can define this on any error class with attr_accessor:
class SomeError
attr_accessor :ignore
alias ignore? ignore
end
1b. Rescue the error, set the custom attribute, & re-raise
def perform
# do something
rescue SomeError => e
e.ignore = true
raise e
end
Configure should_capture
should_capture allows you to capture exceptions when they meet a defined criteria. The exception is passed to it, on which you can access the custom attribute.
config.should_capture { |e| !e.ignore? }
Flip the custom attribute when retries are exhausted
There are 2 ways to define the behaviour you want to happen when a job dies, depending on the version of Sidekiq being used. If you want to apply globally & have sidekiq v5.1+, you can use a death handler. If you want to apply to a particular worker or have less than v5.1, you can use sidekiq_retries_exhausted.
sidekiq_retries_exhausted { |_job, ex| ex.ignore = false }

Answer 2

You can filter out the entire event if the retry_count is < N (can be done inside that sidekiq worker you posted). You will loose the data on how often this happens without alerting, but the alerts themselves will not be too noisy.
class SentryWorker < ApplicationWorker
sidekiq_options queue: :default
def perform(event)
retry_count = event.dig(:extra, :sidekiq, :job, retry_count)
if retry_count.nil? || retry_count > N
Raven.send_event(event)
end
end
end
Another idea is to set a different fingerprint depending on whether this is a retry or not. Like this:
class MyJobProcessor < Raven::Processor
def process(data)
retry_count = event.dig(:extra, :sidekiq, :job, retry_count)
if (retry_count || 0) < N
data["fingerprint"] = ["will-retry-again", "{{default}}"]
end
end
end
See https://docs.sentry.io/learn/rollups/?platform=javascript#custom-grouping
I didn't test this, but this should split up your issues into two, depending on whether sidekiq will retry them. You can then ignore one group but can still look at it whenever you need the data.

Answer 3

A much cleaner approach if you are trying to ignore exceptions belonging to a certain class is to add them to your config file
config.excluded_exceptions += ['ActionController::RoutingError', 'ActiveRecord::RecordNotFound']
In the above example, the exceptions Rails uses to generate 404 responses will be suppressed.
See the docs for more configuration options

Answer 4

From my point of view, the best option is Sentry holds all the exceptions and you could modify Sentry and set alerts to send or not the exceptions to the Slack.
In order to configure the Alerts in Sentry: In the sentry account, you could go to the ALerts option in the main menu.
In the following picture I configure an alert to only send to slack a notification if occurs an Exception of type ControllerException more than 10 times
Using this alert we only receive the notification in Slack when all conditions are accomplished