Make an Event of It! (ConFoo 2014)

Jason Clark
@jasonrclark
Ruby Agent Engineer
Make an Event of It!
Evented Patterns in Ruby
Wednesday, February 26, 14

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2

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3

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Events Aren't
(Necessarily)
4
• Asynchronous
• IO related
• Distributed
• Complicated

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Where Are We Going?
• The Pattern
• Internal Coupling
• External Coupling
• Adding Eventing
• ActiveSupport::Notiﬁcations
• Notiﬁers
• Subscribers
• Events as Data
5

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The Pattern
http://ﬂic.kr/p/6K9jC4

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7
Notiﬁer

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7
Notiﬁer
Subscriber
Subscriber
Subscriber

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7
Notiﬁer
Subscriber
Subscriber
Subscriber
Eventing
System

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8
Why Not Methods?

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9

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9
Notiﬁer
Subscriber
Subscriber
Subscriber
Eventing
System

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Why Not Callbacks?
10

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class Subscription < ActiveRecord::Base
before_create :record_signup
private
def record_signup
self.signed_up_on = Date.today
end
end

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Where Have We Been?
• The Pattern
• Adding Eventing
• Notiﬁers
• Subscribers
• Events as Data
12

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Internal Coupling
http://ﬂic.kr/p/KikA9

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newrelic_rpm

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app start
newrelic_rpm

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app start connect()
New Relic
Server
newrelic_rpm

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{server conﬁg}
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app start connect()
New Relic
Server
newrelic_rpm

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{server conﬁg}
14
app start connect()
New Relic
Server
?
newrelic_rpm

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def connect()
config = config_from_server()
finish_setup(config)
end
newrelic_rpm

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def finish_setup(config)
add_naming_rule(config['rules'])
@cross_app_tracing.set_key(config)
@js_instrumentor.log_config(config)
@beacon = Beacon.new
end
newrelic_rpm

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def test_finish_setup_naming_rules
config = { 'rules' => [...] }
@agent.finish_setup(config)
assert_equal 2, @agent.transaction_rules.size
end
newrelic_rpm

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@agent.cross_app_tracing.stub(:set_key)
@agent.js_instrumentor.stub(:log_config)
config = { 'rules' => [...] }
end
newrelic_rpm

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end
newrelic_rpm

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end
newrelic_rpm

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class Beacon
def initialize
# Your code is bad and you should feel bad
Net::HTTP.get("http://somewhere.com")
end
end
newrelic_rpm

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@agent.cross_app_tracing.stub(:set_key)
@agent.js_instrumentor.stub(:log_config)
Beacon.stub(:new).return(stub("fake beacon"))
config = { 'rules' => [...] }
end
newrelic_rpm

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end
newrelic_rpm

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events.notify(:configured)
end
newrelic_rpm

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class Beacon
def initialize
events.subscribe(:configured) do
Net::HTTP.get("http://...")
end
end
end
newrelic_rpm

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def test_finish_setup_notifies
called = false
@events.subscribe(:configured) do
called = true
end
@agent.finish_setup({})
assert called
end
newrelic_rpm

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def test_add_naming_rules
config = { 'rules' => [...] }
@agent.add_naming_rules(config)
end
newrelic_rpm

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More Independent
Classes
29

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Implicit Ordering
30

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Debugging
31

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Performance
32

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Where Have We Been?
• The Pattern
• Adding Eventing
• Notiﬁers
• Subscribers
• Events as Data
33

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http://ﬂic.kr/p/euQpT
External Coupling

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35
newrelic_rpm

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Javascript insertion
newrelic_rpm

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Error collection
newrelic_rpm

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Cross application tracing
Error collection
newrelic_rpm

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No Setup Please!
newrelic_rpm

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module NewRelic::Rack
class AgentHooks
def call(env)
notify(:before_call, env)
result = @app.call(env)
notify(:after_call, env, result)
result
end
end
end
newrelic_rpm

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38
class CrossAppTracing
def initialize
events.subscribe(:before_call) do |e|
process_request(e)
end
...
end
end
newrelic_rpm

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Ever Heard of
Composition?
39

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Looser Coupling
40

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Compatibilty
Layer
41

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Where Have We Been?
• The Pattern
• Adding Eventing
• Notiﬁers
• Subscribers
• Events as Data
42

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http://ﬂic.kr/p/dYor95
Adding Eventing

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Notiﬁer
Subscriber
Subscriber
Subscriber
Eventing
System

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gem install
simple_events
http://github.com/jasonrclark/simple_events

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class SimpleEvents::Notifier
def initialize
@events = {}
...
end
end
simple_events

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...
def subscribe(event, &handler)
@events[event] ||= []
@events[event] << handler
check_for_runaway_subscriptions(event)
end
...
end
simple_events

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...
def notify(event, *args)
return unless @events.has_key?(event)
@events[event].each do |handler|
begin
handler.call(*args)
rescue => err
logger.debug("Fail #{@event}", err)
end
end
end
end
simple_events

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...
begin
handler.call(*args)
rescue => err
end
end
end
end
simple_events

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...
begin
handler.call(*args)
rescue => err
end
end
end
end
simple_events

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...
begin
handler.call(*args)
rescue => err
end
end
end
end
simple_events

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...
begin
handler.call(*args)
rescue => err
end
end
end
end
simple_events

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Where Have We Been?
• The Pattern
• Adding Eventing
• Notiﬁers
• Subscribers
• Events as Data
53

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ActiveSupport::
Notiﬁcations
http://ﬂic.kr/p/aWNwU2

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AS::Notifications
=
ActiveSupport::Notifications
activesupport

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Rails Request
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•action_dispatch.request
•start_processing.action_controller
•process_action.action_controller
•sql.active_record
•render_template.action_view
• ... and more!

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events = []
AS::Notifications.subscribe("event") do |*args|
events << *args
end
activesupport

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AS::Notifications.subscribe("event") do |*args|
events << *args
end
["render_template.action_view",
"e2a1e92a3c613576c2b0"
{:identifier=>"/file/path/here"}]
activesupport

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e = AS::Notifications::Event.new(*args)
e.name # => "render_template..."
e.duration # => 10 (in milliseconds)
e.payload # => { :identifier => ... }
activesupport

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activesupport
AS::Notifications.instrument("evt", :data => 1)

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AS::Notifications.instrument("evt", :data => 1) do
#... your timed code here
end
activesupport

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• Regexp on Notifications.subscribe
• Event#parent_of?
• Temporary subscription
• Unsubscribe
• LogSubscriber
62
activesupport

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Where Have We Been?
• The Pattern
• Adding Events
• Notiﬁers
• Subscribers
• Events as Data
63

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http://ﬂic.kr/p/a1dEec
Notiﬁers

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Notiﬁer
Subscriber
Subscriber
Subscriber
Eventing
System

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Naming
66

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Flexible Payload
67

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Primitives at
Boundaries
68

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Where Have We Been?
• The Pattern
• Adding Events
• Notiﬁers
• Subscribers
• Events as Data
69

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http://ﬂic.kr/p/8w9PyF
Subscribers

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Notiﬁer
Subscriber
Subscriber
Subscriber
Eventing
System

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!= self.only
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class UserSignup < Mutations::Command
def execute
user = User.create!(inputs)
NewsletterSubscriptions.create(user.id)
UserMailer.async(:deliver_welcome, user.id)
user
end
end

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class SomeSubscriber
def initialize
events.subscribe(:configured) do
log_config
end
end
def log_config
...
end
end

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Memory Leaks
76

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Where Have We Been?
• The Pattern
• Adding Events
• Notiﬁers
• Subscribers
• Events as Data
77

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http://ﬂic.kr/p/ndraB
Events as Data

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Opened Account $100
Check 0001 -$15
Deposit $20
Check 0002 -$21
Total $84
Bank Transactions

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Customer Pricing

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customer_id date plan
1 1/1/2013 basic
1 1/2/2013 premium
1 2/1/2013 basic
1 2/2/2013 premium
Customer Pricing

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Event Sourcing
81

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82 http://ﬂic.kr/p/4LTNc9

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Metrics
10:00AM
CPU/Utilization
0.85

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Metrics
10:01AM
CPU/Utilization
0.24

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Metrics

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Metrics

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Metrics

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Metric Data

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Other Examples
89
• Database replication
• Log ﬁles
• PubSub
• Immutable data structures

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Beneﬁts
90
No Updates
Automatic Audits
Summarize/Transform/
Cache

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Drawbacks
So Much Data!
Hard to Query Efﬁciently
More Complex Code
91

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Jason Clark
@jasonrclark
Ruby Agent Engineer
• The Pattern
• Adding Eventing
• Notiﬁers
• Subscribers
• Events as Data
?

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Make an Event of It! (ConFoo 2014)

Make an Event of It! (ConFoo 2014)

Jason R Clark

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