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How to get to zero unhandled exceptions in production Radoslav Stankov 07/09/2019

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Radoslav Stankov @rstankov blog.rstankov.com github.com/rstankov
 twitter.com/rstankov

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 ! Product Hunt Engineering Team " 


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Happy Friday # $ Fix bugs % Goodies features & Pay technical dept ' Catchup on projects ( Fix exceptions

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Happy Friday # $ Fix bugs % Goodies features & Pay technical dept ' Catchup on projects ( Fix exceptions

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“Have process around exceptions.” 
 ) Tip 


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Back to basics

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 http://exceptionalruby.com/


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def perform do_something rescue end

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def perform do_something rescue SpecificError end

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def perform do_something rescue SpecificError # NOTE(rstankov): Reason to return nil nil end Your name, not mine *

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def perform do_something rescue Timeout::Error # NOTE(rstankov): WiFi Sucks nil end

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“Be explicit around the exceptions. Handle specific errors and have explanations of why they happen.” 
 ) Tip 


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Monitoring

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Raven.configure do |config| # Note(rstankov): Exclude unactionable errors config.excluded_exceptions = [ 'Rack::Timeout::RequestExpiryError', 'Rack::Timeout::RequestTimeoutException', 'ActionController::RoutingError', 'ActionController::InvalidAuthenticityToken', 'ActionDispatch::ParamsParser::ParseError', 'Sidekiq::Shutdown', ] end

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ArgumentError: invalid byte sequence in UTF-8 (

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# NOTE(rstankov): Fix invalid byte sequence in UTF-8. More info: # - https://robots.thoughtbot.com/fight-back-utf-8-invalid-byte-sequences module Handle::InvalidByteSequence extend self def call(string) return if string.nil? string.encode('UTF-8', 'binary', invalid: :replace, undef: :replace, replace: '' ) end end

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“Reduce noise. See only exceptional errors in your tracker.” 
 ) Tip 


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account.subscription.status

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account.subscription&.status

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✅ Check for other accounts without a subscription ✅ Find out why some accounts don't have a subscription ✅ Fix the root problem ✅ Add missing subscriptions to accounts , Steps to fix -

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if account.ship_subscription.blank? Raven.capture_message "Missing ship subscription", extra: { account_id: account.id } return :no_subscription end

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“Don't hide exceptions. Fix root causes.” 
 ) Tip 


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 https://graphql.org/


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Which query causes this issue? .

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class Frontend::GraphqlController < Frontend::BaseController before_action :ensure_query def index render json: Graph::Schema.execute(query, variables: variables, context: context) rescue => e handle_error e end private # ... def handle_error(error) if Rails.env.development? logger.error error.message logger.error error.backtrace.join("\n") render json: { error: { message: error.message, backtrace: error.backtrace } }, status: 500 elsif Rails.env.test? p error.message p error.backtrace render json: { error: { message: error.message, backtrace: error.backtrace } }, status: 500 else Raven.capture_exception(e, extra: { query: query }) render json: { error: { message: 'SERVER_ERROR' }, data: {} }, status: 500 end end end

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class Frontend::GraphqlController < Frontend::BaseController before_action :ensure_query def index render json: Graph::Schema.execute(query, variables: variables, context: context) rescue => e handle_error e end private # ... def handle_error(error) if Rails.env.development? logger.error error.message logger.error error.backtrace.join("\n") render json: { error: { message: error.message, backtrace: error.backtrace } }, status: 500 elsif Rails.env.test? p error.message p error.backtrace render json: { error: { message: error.message, backtrace: error.backtrace } }, status: 500 else Raven.capture_exception(e, extra: { query: query }) render json: { error: { message: 'SERVER_ERROR' }, data: {} }, status: 500 end end end

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class Frontend::GraphqlController < Frontend::BaseController before_action :ensure_query def index render json: Graph::Schema.execute(query, variables: variables, context: context) rescue => e handle_error e end private # ... def handle_error(error) if Rails.env.development? logger.error error.message logger.error error.backtrace.join("\n") render json: { error: { message: error.message, backtrace: error.backtrace } }, status: 500 elsif Rails.env.test? p error.message p error.backtrace render json: { error: { message: error.message, backtrace: error.backtrace } }, status: 500 else Raven.capture_exception(e, extra: { query: query }) render json: { error: { message: 'SERVER_ERROR' }, data: {} }, status: 500 end end end

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“Invest in your monitoring and exception traceability. When you have a hard time racing an exception. Ask yourself - what more information I need? . Then add it.” 
 ) Tip 


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 https://sidekiq.org/


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Use action Achievements::Job Achievement
 (unique)

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class Achievements::Job < ApplicationJob def perform(achievement, user) Achievements::Create.call achievement, user end end

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Use action Achievements::Job Achievement
 (unique) Use action Achievements::Job Achievement
 (unique)

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Use action Achievements::Job Achievement
 (unique) Use action Achievements::Job Achievement
 (unique) (

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Use action Achievements::Job Achievement
 (unique) Use action Achievements::Job PG::UniqueViolation (

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class Achievements::Job < ApplicationJob def perform(achievement, user) Achievements::Create.call achievement, user end end

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class Achievements::Job < ApplicationJob def perform(achievement, user) Handle::RaceCondition.call do Achievements::Create.call achievement, user end end end

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module Handle::RaceCondition extend self UNIQUE_ACTIVE_RECORD_ERROR = 'has already been taken'.freeze def call retries ||= 2 yield rescue ActiveRecord::RecordNotUnique, PG::UniqueViolation retries -= 1 raise unless retries.nonzero? retry rescue ActiveRecord::RecordInvalid => e raise unless e.message.include? UNIQUE_ACTIVE_RECORD_ERROR retries -= 1 raise unless retries.nonzero? retry end end

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class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event) end end

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Errno::ECONNRESET (

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class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event) end end

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class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event)
 rescue Errno::ECONNRESET
 retry_job end end

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class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event)
 rescue Errno::ECONNRESET, EOFError
 retry_job end end

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class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event)
 rescue Errno::ECONNRESET, EOFError, Timeout::Error
 retry_job end end

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class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event)
 rescue Errno::ECONNRESET, EOFError, Timeout::Error, ... /
 retry_job end end

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module Handle::NetworkErrors extend self ERRORS = [ EOFError, Errno::ECONNRESET, Errno::EINVAL, Net::HTTPBadResponse, Net::HTTPHeaderSyntaxError, Net::ProtocolError, Timeout::Error, # ... ] def ===(error) ERRORS.any? { |error_class| error_class === error } end end

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class Notifications::Deliver < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event)
 rescue Handle::NetworkErrors retry_job end end

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class Notifications::Deliver::Job < ApplicationJob retry_on(*::Handle::NetworkErrors::ERRORS, wait: 2.minutes, attempts: 5) queue_as :notifications def perform(event) Notifications::Deliver.call(event) end end

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class Notifications::Deliver::Job < ApplicationJob include Handle::Job::NetworkErrors queue_as :notifications def perform(event) Notifications::Deliver.call(event) end end

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module Handle::Job::NetworkErrors def self.included(job) job.retry_on(*::Handle::NetworkErrors::ERRORS, wait: 2.minutes, attempts: 5) end end

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module Handle::NetworkErrors extend self ERRORS = [ # ... Faraday::ConnectionFailed, Faraday::TimeoutError, RestClient::BadGateway, RestClient::BadRequest, # ... ] def ===(error) ERRORS.any? { |error_class| error_class === error } end end

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“Have tooling around handling common exceptions. Make it a no-brainer to process everyday errors.” 
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Recap

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) Have process around exceptions.
 ) Be explicit around the exceptions
 ) Reduce noise
 ) Don't hide exceptions
 ) Invest in your monitoring
 ) Have tooling around handling common exceptions 
 1 Recap 


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Thanks 2

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https://speakerdeck.com/rstankov