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How to get to zero unhandled exceptions in production Radoslav Stankov 26/05/2018

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

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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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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 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 NetworkErrors # NOTE(rstankov): WiFi Sucks nil end

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module 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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– saw it in a tweet once “A mature Rails project is one, that uses every popular (or not so popular) Ruby networking gem.” (

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– saw it in a tweet once “A mature Rails project is one, that uses every popular (or not so popular) Ruby networking gem.” (

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

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Monitoring

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

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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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0. Check for other accounts without subscription Steps to fix )

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0. Check for other accounts without subscription 1. Find out why account doesn't have a subscription Steps to fix )

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0. Check for other accounts without subscription 1. Find out why account doesn't have a subscription 2. Fix the problem Steps to fix )

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0. Check for other accounts without subscription 1. Find out why account doesn't have a subscription 2. Fix the problem 3. Add missing subscriptions to this accounts Steps to fix )

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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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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 Utf8Sanitize 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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 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(e) if Rails.env.development? logger.error e.message logger.error e.backtrace.join("\n") render json: { message: e.message, backtrace: e.backtrace }, status: 500 elsif Rails.env.test? p e.message # rubocop:disable Rails/Output p e.backtrace # rubocop:disable Rails/Output else Raven.capture_exception(e, extra: { query: query }) 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(e) if Rails.env.development? logger.error e.message logger.error e.backtrace.join("\n") render json: { message: e.message, backtrace: e.backtrace }, status: 500 elsif Rails.env.test? p e.message # rubocop:disable Rails/Output p e.backtrace # rubocop:disable Rails/Output else Raven.capture_exception(e, extra: { query: query }) 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(e) if Rails.env.development? logger.error e.message logger.error e.backtrace.join("\n") render json: { message: e.message, backtrace: e.backtrace }, status: 500 elsif Rails.env.test? p e.message # rubocop:disable Rails/Output p e.backtrace # rubocop:disable Rails/Output else Raven.capture_exception(e, extra: { query: query }) end end end

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Graph::Query = GraphQL::ObjectType.define do name 'Query' field :post do type !Graph::Types::PostType argument :id, !types.ID resolve ->(_obj, inputs, _ctx) { Post.find(inputs[:id]) } end end

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Graph::Query = GraphQL::ObjectType.define do name 'Query' field :post do type Graph::Types::PostType argument :id, !types.ID resolve ->(_obj, inputs, _ctx) { Post.find_by(id: inputs[:id]) } end end

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class Graph::Mutations::CollectionAddPost < Graph::Resolvers::Mutation node :collection, type: Collection input :post_id, !types.ID authorize: Authorization::MANAGE returns Graph::Types::PostType def perform post = Post.find inputs[:post_id] Collections.add_post collection, post post end end

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class Graph::Resolvers::Mutation # ... def call pre_proccess handle_result perform rescue ActiveRecord::RecordInvalid, MiniForm::InvalidForm => e errors_from_record(e.record) rescue ActiveRecord::RecordNotFound error :base, :record_not_found rescue CanCan::AccessDenied error_access_denied end # ... end

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 https://sidekiq.org/


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

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module HandleRaceCondition 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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Notifications::FanOutWorker Notifications::ScheduleWorker Notifications::DeliveryWorker Notifications.notify_about :kind, object

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Notifications::FanOutWorker Notifications::ScheduleWorker Notifications::DeliveryWorker Notifications.notify_about :kind, object kind, object

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Notifications::FanOutWorker Notifications::ScheduleWorker Notifications::DeliveryWorker Notifications.notify_about :kind, object kind, object kind, object, subscriber

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Notifications::FanOutWorker Notifications::ScheduleWorker Notifications::DeliveryWorker Notifications.notify_about :kind, object kind, object kind, object, subscriber kind, object, subscriber, channel

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class Notifications::ScheduleWorker < ApplicationJob include ActiveJobHandleDeserializationError 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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module ActiveJobHandleDeserializationError include ActiveJobRetriesCount extend ActiveSupport::Concern included do rescue_from ActiveJob::DeserializationError do retry_job wait: 5.minutes if retries_count.zero? end end end

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module ActiveJobHandleDeserializationError include ActiveJobRetriesCount extend ActiveSupport::Concern included do rescue_from ActiveJob::DeserializationError do retry_job wait: 5.minutes if retries_count.zero? end end end

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module ActiveJobRetriesCount extend ActiveSupport::Concern included do attr_accessor :retries_count end def initialize(*arguments) super @retries_count ||= 0 end def deserialize(job_data) super @retries_count = job_data['retries_count'] || 0 end def serialize hash = super.merge('retries_count' => retries_count || 0) # NOTE(rstankov): Workaround for Rails bug # When arguments raise `ActiveJob::DeserializationError` arguments are blank hash['arguments'] ||= @serialized_arguments if @serialized_arguments hash end def retry_job(options) @retries_count = (retries_count || 0) + 1 super(options) end end

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

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module ActiveJobHandleNetworkErrors include ActiveJobRetriesCount extend ActiveSupport::Concern included do rescue_from(NetworkErrors) do if retries_count <= 10 retry_job wait: 5.minutes else
 raise e end end end end

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Thanks +