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Living without Exceptions Radoslav Stankov 07/09/2019

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!

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Radoslav Stankov @rstankov rstankov.com

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https://tips.rstankov.com

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" Happy Friday # Bug Duty ⚔ Strike Team 4 8 20 developers count

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1 developers count " Happy Friday

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% Fix bugs & Fix exceptions ' Bump dependancies ( Pay technical dept ) Catchup on projects " Happy Friday

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% Fix bugs & Fix exceptions ' Bump dependancies ( Pay technical dept ) Catchup on projects " Happy Friday

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% Fix bugs & Fix exceptions ' Bump dependancies ( Pay technical dept ) Catchup on projects " Happy Friday

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“Have process around exceptions.” * Rado's 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 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

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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 SpecificError # NOTE(rstankov): Reason to return nil nil end

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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.” * Rado's tip

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Monitoring

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“Split web and background processes errors into separate projects” * Rado's tip

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＃engineering-exceptions

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“Have a Slack channel where every new exception is being logged. Log deployments in this channel as well, so you can correlate.” * Rado's tip

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– Brian Kernighan and Rob Pike, The Practice of Programming “Exceptions shouldn't be expected” Use exceptions only for exceptional situations. […] Exceptions are often overused. Because they distort the flow of control, they can lead to convoluted constructions that are prone to bugs. It is hardly exceptional to fail to open a file; generating an exception in this case strikes us as over-engineering.

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Sentry.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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“Reduce noise. See only exceptional errors in your tracker.” * Rado's tip

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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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“I put most of the code related to exceptions in a single module named Handle” * Rado's tip

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account.subscription.status

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account.subscription&.status

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account.subscription&.status

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, Steps to fix -

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✅ Check for other accounts without a subscription , Steps to fix -

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✅ Check for other accounts without a subscription , Steps to fix -

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✅ Check for other accounts without a subscription ✅ Find out why those accounts don't have a subscription , Steps to fix -

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✅ Check for other accounts without a subscription ✅ Find out why those accounts don't have a subscription , Steps to fix -

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✅ Check for other accounts without a subscription ✅ Find out why those accounts don't have a subscription ✅ Fix this / , Steps to fix -

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✅ Check for other accounts without a subscription ✅ Find out why those accounts don't have a subscription ✅ Fix this / , Steps to fix -

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✅ Check for other accounts without a subscription ✅ Find out why those accounts don't have a subscription ✅ Fix this / ✅ Add missing subscriptions to accounts , Steps to fix -

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“Don't hide exceptions. Fix root causes.” * Rado's tip

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if account.ship_subscription.blank? ErrorReporting.capture "Missing ship subscription", account_id: account.id return :no_subscription end

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“I have a module named ErrorReporting, which helps me capture errors that won't get to the user and provides a centralized place for error tracking.” * Rado's tip

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https://graphql.org/

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Which query causes this issue? 0

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class Frontend::GraphqlController < Frontend::BaseController before_action :authenticate def index render json: Graph::Schema.execute(query, variables: variables, context: context) rescue => e handle_error e end private def authenticate # ... 
 ErrorReporting.assign_user(@user) end
 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 ErrorReporting.capture(e, 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 :authenticate def index render json: Graph::Schema.execute(query, variables: variables, context: context) rescue => e handle_error e end private def authenticate # ... 
 ErrorReporting.assign_user(@user) end
 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 ErrorReporting.capture(e, 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 :authenticate def index render json: Graph::Schema.execute(query, variables: variables, context: context) rescue => e handle_error e end private def authenticate # ... 
 ErrorReporting.assign_user(@user) end
 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 ErrorReporting.capture(e, 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 :authenticate def index render json: Graph::Schema.execute(query, variables: variables, context: context) rescue => e handle_error e end private def authenticate # ... 
 ErrorReporting.assign_user(@user) end
 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 ErrorReporting.capture(e, 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? 0 Then add it.” * Tip

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https://sidekiq.org/

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Use action

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Use action Achievements::Job

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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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Errno:: EOFError &

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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, ... 1
 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: 50 ) do |job, exception| ErrorReporting.job_discarded(job, exception) end end end

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module Handle::Job::NetworkErrors def self.included(job) job.retry_on( *::Handle::NetworkErrors::ERRORS, wait: 2.minutes, attempts: 50 ) do |job, exception| ErrorReporting.job_discarded(job, exception) end end end

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2

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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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ActiveJob::DeserializationError &

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class Notifications::ScheduleJob < ApplicationJob queue_as :notifications def perform(kind:, object:, subscriber_id:) Notifications::Schedule.call( kind: kind, object: object, subscriber_id: subscriber_id, ) end end

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class Notifications::ScheduleJob < ApplicationJob include Handle::Job::DeserializationError queue_as :notifications def perform(kind:, object:, subscriber_id:) Notifications::Schedule.call( kind: kind, object: object, subscriber_id: subscriber_id, ) end end

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“Have tooling around handling common exceptions. Make it a no-brainer to process everyday errors.” * Rado's tip

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Recap

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* Be explicit around the exceptions * Reduce noise * Don't hide exceptions * Invest in your monitoring * Have tooling around handling exceptions 3 Recap

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https://tips.rstankov.com/p/tips-exceptions

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