1. Building
Reactive Systems
with Akka
Jonas Bonér
Typesafe
CTO & co-founder
Twitter: @jboner

2. The rules of the game
have changed

3. 3
Apps in the 60s-90s
were written for
Apps today
are written for

4. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines

5. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines

6. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors

7. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors

8. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM

9. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM

10. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk

11. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk

12. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk
Slow networks

13. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk
Slow networks Fast networks

14. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk
Slow networks Fast networks
Few concurrent users

15. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk
Slow networks Fast networks
Few concurrent users Lots of concurrent users

16. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk
Slow networks Fast networks
Few concurrent users Lots of concurrent users
Small data sets

17. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk
Slow networks Fast networks
Few concurrent users Lots of concurrent users
Small data sets Large data sets

18. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk
Slow networks Fast networks
Few concurrent users Lots of concurrent users
Small data sets Large data sets
Latency in seconds

19. 3
Apps in the 60s-90s
were written for
Apps today
are written for
Single machines Clusters of machines
Single core processors Multicore processors
Expensive RAM Cheap RAM
Expensive disk Cheap disk
Slow networks Fast networks
Few concurrent users Lots of concurrent users
Small data sets Large data sets
Latency in seconds Latency in milliseconds

21. Cost Gravity is at Work
X

22. Cost Gravity is at Work
X

23. Reactive applications share four traits
Reactive
Applications
5

24. Reactive applications enrich the user
experience with low latency response.

25. Responsive
• Real-time, engaging, rich and collaborative
• Create an open and ongoing dialog with users
• More efficient workflow; inspires a feeling of connectedness
• Fully Reactive enabling push instead of pull
7
“The move to these technologies is already paying off.
Response times are down for processor intensive code–such as image
and PDF generation–by around 75%.”
Brian Pugh, VP of Engineering, Lucid Software

26. Reactive applications react to
changes in the world around them.

27. Message-Driven
• Loosely coupled architecture, easier to extend, maintain, evolve
• Asynchronous and non-blocking
• Concurrent by design, immutable state
• Lower latency and higher throughput
9
“Clearly, the goal is to do these operations concurrently and
non-blocking, so that entire blocks of seats or sections are not locked.
We’re able to find and allocate seats under load in less than 20ms
without trying very hard to achieve it.”
Andrew Headrick, Platform Architect, Ticketfly

28. Introducing the Actor Model

29. 11
The Actor Model

30. 11
The Actor Model
A computational model that embodies:

31. 11
The Actor Model
A computational model that embodies:
✓ Processing

32. 11
The Actor Model
A computational model that embodies:
✓ Processing
✓ Storage

33. 11
The Actor Model
A computational model that embodies:
✓ Processing
✓ Storage
✓ Communication

34. A computational model that embodies:
✓ Processing
✓ Storage
✓ Communication
Supports 3 axioms—when an Actor receives a message it can:
11
The Actor Model

35. A computational model that embodies:
✓ Processing
✓ Storage
✓ Communication
Supports 3 axioms—when an Actor receives a message it can:
1. Create new Actors
11
The Actor Model

36. A computational model that embodies:
✓ Processing
✓ Storage
✓ Communication
Supports 3 axioms—when an Actor receives a message it can:
1. Create new Actors
2. Send messages to Actors it knows
11
The Actor Model

37. A computational model that embodies:
✓ Processing
✓ Storage
✓ Communication
Supports 3 axioms—when an Actor receives a message it can:
1. Create new Actors
2. Send messages to Actors it knows
3. Designate how it should handle the next message it receives
11
The Actor Model

38. The essence of an actor
from Akka’s perspective
0. DEFINE
1. CREATE
2. SEND
3. BECOME
4. SUPERVISE
12

39. public class Greeting implements Serializable {
public final String who;
public Greeting(String who) { this.who = who; }
}
!
public class Greeter extends AbstractActor {{
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchAny(unknown -> {
println(“Unknown message " + unknown);
}).build());
}}
0. DEFINE
X

40. public class Greeting implements Serializable {
public final String who;
public Greeting(String who) { this.who = who; }
}
!
public class Greeter extends AbstractActor {{
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchAny(unknown -> {
println(“Unknown message " + unknown);
}).build());
}}
0. DEFINE
X
Define the message(s) the Actor
should be able to respond to

41. public class Greeting implements Serializable {
public final String who;
public Greeting(String who) { this.who = who; }
}
!
public class Greeter extends AbstractActor {{
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchAny(unknown -> {
println(“Unknown message " + unknown);
}).build());
}}
0. DEFINE
X
Define the message(s) the Actor
should be able to respond to
Define the Actor class

42. public class Greeting implements Serializable {
public final String who;
public Greeting(String who) { this.who = who; }
}
!
public class Greeter extends AbstractActor {{
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchAny(unknown -> {
println(“Unknown message " + unknown);
}).build());
}}
0. DEFINE
X
Define the message(s) the Actor
should be able to respond to
Define the Actor class
Define the Actor’s behavior

43. 1. CREATE
ActorSystem system = ActorSystem.create("MySystem");
!
ActorRef greeter =
system.actorOf(Props.create(Greeter.class), “greeter");

44. 1. CREATE
Create an Actor system
ActorSystem system = ActorSystem.create("MySystem");
!
ActorRef greeter =
system.actorOf(Props.create(Greeter.class), “greeter");

45. 1. CREATE
Create an Actor system
Actor configuration
ActorSystem system = ActorSystem.create("MySystem");
!
ActorRef greeter =
system.actorOf(Props.create(Greeter.class), “greeter");

46. 1. CREATE
Create an Actor system
Actor configuration
ActorSystem system = ActorSystem.create("MySystem");
!
ActorRef greeter =
system.actorOf(Props.create(Greeter.class), “greeter");
Give it a name

47. 1. CREATE
Create an Actor system
ActorSystem system = ActorSystem.create("MySystem");
!
ActorRef greeter =
system.actorOf(Props.create(Greeter.class), “greeter");
Give it a name
Create the Actor
Actor configuration

48. 1. CREATE
Create an Actor system
ActorSystem system = ActorSystem.create("MySystem");
!
ActorRef greeter =
system.actorOf(Props.create(Greeter.class), “greeter");
Give it a name
You get an ActorRef back
Create the Actor
Actor configuration

49. 0. DEFINE
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
13
case Greeting(who) => log.info(s"Hello ${who}")
}
}

50. 0. DEFINE
13
Define the message(s) the Actor
should be able to respond to
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
case Greeting(who) => log.info(s"Hello ${who}")
}
}

51. 0. DEFINE
13
Define the message(s) the Actor
should be able to respond to
Define the Actor class
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
case Greeting(who) => log.info(s"Hello ${who}")
}
}

52. 0. DEFINE
13
Define the message(s) the Actor
should be able to respond to
Define the Actor class
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
case Greeting(who) => log.info(s"Hello ${who}")
}
}
Define the Actor’s behavior

53. 1. CREATE
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
case Greeting(who) => log.info("Hello " + who)
}
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")

54. 1. CREATE
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
Create an Actor system
case Greeting(who) => log.info("Hello " + who)
}
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")

55. 1. CREATE
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
Create an Actor system
case Greeting(who) => log.info("Hello " }
Actor configuration
+ who)
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")

56. 1. CREATE
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
case Greeting(who) => log.info("Hello " + who)
}
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")
Give it a name
Create an Actor system
Actor configuration

57. 1. CREATE
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
Create an Actor system
case Greeting(who) => log.info("Hello " }
Actor configuration
+ who)
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")
Give it a name
Create the Actor

58. 1. CREATE
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
Create an Actor system
case Greeting(who) => log.info("Hello " }
Actor configuration
+ who)
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")
Give it a name
You get an ActorRef bCarcekate the Actor

59. Actors can form hierarchies
Guardian System Actor

60. Actors can form hierarchies
Guardian System Actor
system.actorOf(Props.create(Foo.class), “Foo”);

61. Actors can form hierarchies
Foo
Guardian System Actor
system.actorOf(Props.create(Foo.class), “Foo”);

62. Actors can form hierarchies
Foo
Guardian System Actor
context().actorOf(Props.create(A.class), “A”);

63. Actors can form hierarchies
A
Foo
Guardian System Actor
context().actorOf(Props.create(A.class), “A”);

64. Actors can form hierarchies
A
Foo Bar
B
C
B
E
A
D
C
Guardian System Actor

65. Actors can form hierarchies
Guardian System Actor

66. Actors can form hierarchies
Guardian System Actor
system.actorOf(Props[Foo], “Foo”)

67. Actors can form hierarchies
Foo
Guardian System Actor
system.actorOf(Props[Foo], “Foo”)

68. Actors can form hierarchies
Foo
Guardian System Actor
context.actorOf(Props[A], “A”)

69. Actors can form hierarchies
A
Foo
Guardian System Actor
context.actorOf(Props[A], “A”)

70. Actors can form hierarchies
A
Foo Bar
B
C
B
E
A
D
C
Guardian System Actor

71. Name resolution—like a file-system
A
Foo Bar
B
C
B
E
A
D
C
Guardian System Actor

72. Name resolution—like a file-system
A
Foo Bar
B
C
B
E
A
D
C
/Foo
Guardian System Actor

73. Name resolution—like a file-system
A
Foo Bar
B
C
B
E
A
D
C
/Foo
/Foo/A
Guardian System Actor

74. Name resolution—like a file-system
A
Foo Bar
B
C
B
E
A
D
C
/Foo
/Foo/A
/Foo/A/B
Guardian System Actor

75. Name resolution—like a file-system
A
Foo Bar
B
C
B
E
A
D
C
/Foo
/Foo/A
/Foo/A/B
/Foo/A/D
Guardian System Actor

76. 2. SEND
X
greeter.tell(new Greeting("Charlie Parker”), sender);

77. 2. SEND
X
greeter.tell(new Greeting("Charlie Parker”), sender);
Send the message asynchronously

78. 2. SEND
X
Pass in the sender ActorRef
greeter.tell(new Greeting("Charlie Parker”), sender);
Send the message asynchronously

79. Bring it together
X
public class Greeting implements Serializable {
public final String who;
public Greeting(String who) { this.who = who; }
}
public class Greeter extends AbstractActor {{
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchAny(unknown -> {
println(“Unknown message " + unknown);
}).build());
}
}}
!
ActorSystem system = ActorSystem.create("MySystem");
ActorRef greeter = system.actorOf(Props.create(Greeter.class), “greeter");
greeter.tell(new Greeting(“Charlie Parker”));

80. 2. SEND
17
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
case Greeting(who) => log.info(s”Hello ${who}")
}
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")
greeter ! Greeting("Charlie Parker")

81. 2. SEND
17
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
case Greeting(who) => log.info(s”Hello ${who}")
}
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")
greeter ! Greeting("Charlie Parker")
Send the message asynchronously

82. Bring it together
18
case class Greeting(who: String)
!
class GreetingActor extends Actor with ActorLogging {
def receive = {
case Greeting(who) => log.info(s”Hello ${who}")
}
}
!
val system = ActorSystem("MySystem")
val greeter = system.actorOf(Props[GreetingActor], name = "greeter")
greeter ! Greeting("Charlie Parker")

83. DEMO TIME A simple game of ping pong

84. 3. BECOME
X
public class Greeter extends AbstractActor {
public Greeter {
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchEquals(“stop" -> {
!!!! }).build();
}
}

85. 3. BECOME
X
public class Greeter extends AbstractActor {
public Greeter {
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchEquals(“stop" -> {
!!!! }).build();
}
}
context().become(ReceiveBuilder.

86. 3. BECOME
X
public class Greeter extends AbstractActor {
public Greeter {
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchEquals(“stop" -> {
!!!! }).build();
}
}
Change the behavior
context().become(ReceiveBuilder.

87. 3. BECOME
X
public class Greeter extends AbstractActor {
public Greeter {
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchEquals(“stop" -> {
!!!! }).build();
}
}
Change the behavior
context().become(ReceiveBuilder.
match(Greeting.class, m -> {

88. 3. BECOME
X
public class Greeter extends AbstractActor {
public Greeter {
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchEquals(“stop" -> {
!!!! }).build();
}
}
Change the behavior
context().become(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Go Away!”);

89. 3. BECOME
X
public class Greeter extends AbstractActor {
public Greeter {
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchEquals(“stop" -> {
!!!! }).build();
}
}
Change the behavior
context().become(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Go Away!”);
}).build());

90. 3. BECOME
X
public class Greeter extends AbstractActor {
public Greeter {
receive(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Hello " + m.who);
}).
matchEquals(“stop" -> {
!!!! }).build();
}
}
Change the behavior
context().become(ReceiveBuilder.
match(Greeting.class, m -> {
println(“Go Away!”);
}).build());

91. 3. BECOME
19
class GreetingActor extends Actor with ActorLogging {
def receive = happy
!
val happy: Receive = {
case Greeting(who) => log.info(s”Hello ${who}")
case Angry => context become angry
}
!
val angry: Receive = {
case Greeting(_) => log.info("Go away!")
case Happy => context become happy
}
}

92. 3. BECOME
19
class GreetingActor extends Actor with ActorLogging {
def receive = happy
!
val happy: Receive = {
case Greeting(who) => log.info(s”Hello ${who}")
case Angry => context become angry
}
!
val angry: Receive = {
case Greeting(_) => log.info("Go away!")
case Happy => context become happy
}
}
Redefine the behavior

93. Reactive applications are architected
to handle failure at all levels.

94. Resilient
• Failure is embraced as a natural state in the app lifecycle
• Resilience is a first-class construct
• Failure is detected, isolated, and managed
• Applications self heal
21
“The Typesafe Reactive Platform helps us maintain a very
aggressive development and deployment cycle, all in a fail-forward manner.
It’s now the default choice for developing all new services.”
Peter Hausel, VP Engineering, Gawker Media

95. Think Vending Machine

96. Think Vending Machine
Coffee
Programmer Machine

97. Think Vending Machine
Coffee
Inserts coins
Programmer Machine

98. Think Vending Machine
Coffee
Inserts coins
Add more coins
Programmer Machine

99. Think Vending Machine
Coffee
Inserts coins
Add more coins
Programmer Machine
Gets coffee

100. Think Vending Machine
Coffee
Programmer Machine

101. Think Vending Machine
Coffee
Inserts coins
Programmer Machine

102. Think Vending Machine
Coffee
Inserts coins
Out of coffee beans error
Programmer Machine

103. Think Vending Machine
Coffee
Inserts coins
OutW of corfofeen begans error
Programmer Machine

104. Think Vending Machine
Coffee
Inserts coins
Programmer Machine

105. Think Vending Machine
Coffee
Inserts coins
Out of
coffee beans
error
Programmer Machine

106. Think Vending Machine
Service
Guy
Coffee
Inserts coins
Out of
coffee beans
error
Programmer Machine

107. Think Vending Machine
Service
Guy
Coffee
Inserts coins
Out of
coffee beans
error
Programmer Machine
Adds
more
beans

108. Think Vending Machine
Service
Guy
Coffee
Inserts coins
Programmer Machine
Gets coffee
Out of
coffee beans
error
Adds
more
beans

109. The Right Way
Client Service

110. The Right Way
Request
Client Service

111. The Right Way
Request
Client Service
Response

112. The Right Way
Request
Validation Error
Client Service
Response

113. The Right Way
Request
Validation Error
Client Service
Response
Application
Error

114. The Right Way
Supervisor
Request
Validation Error
Client Service
Response
Application
Error

115. The Right Way
Supervisor
Request
Validation Error
Client Service
Response
Application
Error
Manages
Failure

117. Use Bulkheads
• Isolate the failure
• Compartmentalize
• Manage failure locally
• Avoid cascading failures

118. Use Bulkheads
• Isolate the failure
• Compartmentalize
• Manage failure locally
• Avoid cascading failures

119. Enter Supervision

120. Enter Supervision

121. Supervisor hierarchies
A
Foo Bar
B
C
B
E
A
D
C
Automatic and mandatory supervision

122. 4. SUPERVISE
X
Every single actor has a default supervisor strategy.
Which is usually sufficient.
But it can be overridden.
class Supervisor extends UntypedActor {
private SupervisorStrategy strategy = new OneForOneStrategy(
10, Duration.create(1, TimeUnit.MINUTES),
DeciderBuilder.
match(ArithmeticException.class, e -> resume()).
match(NullPointerException.class, e -> restart()).
matchAny( e -> escalate()).
build());
!
@Override public SupervisorStrategy supervisorStrategy() {
return strategy;
}

123. 4. SUPERVISE
X
class Supervisor extends UntypedActor {
private SupervisorStrategy strategy = new OneForOneStrategy(
10, Duration.create(1, TimeUnit.MINUTES),
DeciderBuilder.
match(ArithmeticException.class, e -> resume()).
match(NullPointerException.class, e -> restart()).
matchAny( e -> escalate()).
build());
!
@Override public SupervisorStrategy supervisorStrategy() {
return strategy;
}
ActorRef worker = context.actorOf(
Props.create(Worker.class), "worker");
public void onReceive(Object i) throws Exception {
…
}
}

124. Monitor through Death Watch
X
public class WatchActor extends AbstractActor {
final ActorRef child = context().actorOf(Props.empty(), "child");
!
public WatchActor() {
context().watch(child);
receive(ReceiveBuilder.
match(Terminated.class,
t -> t.actor().equals(child),
t -> {
… // handle termination
}).build()
);
}
}

125. Monitor through Death Watch
X
public class WatchActor extends AbstractActor {
final ActorRef child = context().actorOf(Props.empty(), "child");
!
public WatchActor() {
context().watch(child);
receive(ReceiveBuilder.
match(Terminated.class,
t -> t.actor().equals(child),
t -> {
… // handle termination
}).build()
);
}
}
Create a child actor

126. Monitor through Death Watch
X
public class WatchActor extends AbstractActor {
final ActorRef child = context().actorOf(Props.empty(), "child");
!
public WatchActor() {
context().watch(child);
receive(ReceiveBuilder.
match(Terminated.class,
t -> t.actor().equals(child),
t -> {
… // handle termination
}).build()
);
}
}
Create a child actor
Watch it

127. Monitor through Death Watch
X
public class WatchActor extends AbstractActor {
final ActorRef child = context().actorOf(Props.empty(), "child");
!
public WatchActor() {
context().watch(child);
receive(ReceiveBuilder.
match(Terminated.class,
t -> t.actor().equals(child),
t -> {
… // handle termination
}).build()
);
}
}
Create a child actor
Watch it
Handle termination message

128. 4. SUPERVISE
29
Every single actor has a default
supervisor strategy.
Which is usually sufficient.
But it can be overridden.

129. 4. SUPERVISE
29
Every single actor has a default
supervisor strategy.
Which is usually sufficient.
But it can be overridden.
class Supervisor extends Actor {
override val supervisorStrategy =
OneForOneStrategy(maxNrOfRetries = 10, withinTimeRange = 1 minute) {
case _: ArithmeticException => Resume
case _: NullPointerException => Restart
case _: Exception => Escalate
}
!
val worker = context.actorOf(Props[Worker], name = "worker")
!
def receive = {

130. 4. SUPERVISE
29
class Supervisor extends Actor {
override val supervisorStrategy =
OneForOneStrategy(maxNrOfRetries = 10, withinTimeRange = 1 minute) {
case _: ArithmeticException => Resume
case _: NullPointerException => Restart
case _: Exception => Escalate
}
!
val worker = context.actorOf(Props[Worker], name = "worker")
!
def receive = {
case n: Int => worker forward n
}
}
!

131. Cleanup & (Re)initialization
30
class Worker extends Actor {
...
override def preRestart(
reason: Throwable, message: Option[Any]) {
... // clean up before restart
}
override def postRestart(reason: Throwable) {
... // init after restart
}
}

132. Monitor through Death Watch
31
class Watcher extends Actor {
val child = context.actorOf(Props.empty, "child")
context.watch(child)
!
def receive = {
case Terminated(`child`) => … // handle child termination
}
}

133. Monitor through Death Watch
31
Create a child actor
class Watcher extends Actor {
val child = context.actorOf(Props.empty, "child")
context.watch(child)
!
def receive = {
case Terminated(`child`) => … // handle child termination
}
}

134. Monitor through Death Watch
31
Create a child actor
Watch it
class Watcher extends Actor {
val child = context.actorOf(Props.empty, "child")
context.watch(child)
!
def receive = {
case Terminated(`child`) => … // handle child termination
}
}

135. Monitor through Death Watch
31
Create a child actor
Watch it
class Watcher extends Actor {
val child = context.actorOf(Props.empty, "child")
context.watch(child)
Handle termination message
!
def receive = {
case Terminated(`child`) => … // handle child termination
}
}

136. Reactive applications scale up
and down to meet demand.

137. Elastic
• Elasticity and Scalability to embrace the Cloud
• Adaptive Scale on Demand
• Clustered servers support joining and leaving of nodes
• More cost-efficient utilization of hardware
33
“Our traffic can increase by as much as 100x for 15 minutes each day.
Until a couple of years ago, noon was a stressful time.
Nowadays, it’s usually a non-event.”
Eric Bowman, VP Architecture, Gilt Groupe

138. 34
Scale UP
Scale OUT

139. 34
Essentially the same thing

140. 35
We need to
1. Minimize Contention
2. Maximize Locality of Reference

141. 36
Share
NOTHING
Design

142. Fully event-driven apps are a necessity
X
Amdahl’s Law will hunt you down

143. Define a router
ActorRef router = context().actorOf(
new RoundRobinPool(5).props(Props.create(Worker.class)),
“router”)
X

144. Define a router
37
val router = context.actorOf(
RoundRobinPool(5).props(Props[Worker])), “router”)

145. …or from config
38
akka.actor.deployment {
/service/router {
router = round-robin-pool
resizer {
lower-bound = 12
upper-bound = 15
}
}
}

146. Turn on clustering
39
akka {
actor {
provider = "akka.cluster.ClusterActorRefProvider"
...
}
cluster {
seed-nodes = [
“akka.tcp://ClusterSystem@127.0.0.1:2551",
“akka.tcp://ClusterSystem@127.0.0.1:2552"
]
auto-down = off
}
}

147. Use clustered routers
40
akka.actor.deployment
{
/service/master
{
router
=
consistent-­‐hashing-­‐pool
nr-­‐of-­‐instances
=
100
!
cluster
{
enabled
=
on
max-nr-of-instances-per-node = 3
allow-­‐local-­‐routees
=
on
use-­‐role
=
compute
}
}
}

148. Use clustered routers
40
Or perhaps use an
AdaptiveLoadBalancingPool
akka.actor.deployment
{
/service/master
{
router
=
consistent-­‐hashing-­‐pool
nr-­‐of-­‐instances
=
100
!
cluster
{
enabled
=
on
max-nr-of-instances-per-node = 3
allow-­‐local-­‐routees
=
on
use-­‐role
=
compute
}
}
}

149. Use clustered pub-sub
41

150. Use clustered pub-sub
41
class Subscriber extends Actor {
val mediator =
DistributedPubSubExtension(context.system).mediator
mediator ! Subscribe(“content”, self)
def receive = { … }
}

151. Use clustered pub-sub
41
class Publisher extends Actor {
val mediator =
DistributedPubSubExtension(context.system).mediator
def receive = {
case in: String =>
mediator ! Publish("content", in.toUpperCase)
}
}

152. • Cluster Membership
• Cluster Pub/Sub
• Cluster Leader
• Clustered Singleton
• Cluster Roles
• Cluster Sharding
42
Other Akka Cluster features

153. • Supports two different models:
• Command Sourcing
• Event Sourcing
• Great for implementing
• durable actors
• replication
• CQRS etc.
• Messages persisted to Journal and replayed on restart
43
Use Akka Persistence

154. X
Command Sourcing Event Sourcing

155. X
Command Sourcing Event Sourcing
write-ahead-log

156. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command

157. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command
same behavior during recovery
as normal operation

158. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command
same behavior during recovery
as normal operation
only state-changing behavior
during recovery

159. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command
same behavior during recovery
as normal operation
only state-changing behavior
during recovery
persisted before validation

160. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command
same behavior during recovery
as normal operation
only state-changing behavior
during recovery
persisted before validation events cannot fail

161. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command
same behavior during recovery
as normal operation
only state-changing behavior
during recovery
persisted before validation events cannot fail
allows retroactive changes to
the business logic

162. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command
same behavior during recovery
as normal operation
only state-changing behavior
during recovery
persisted before validation events cannot fail
allows retroactive changes to
the business logic
fixing the business logic will not
affect persisted events

163. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command
same behavior during recovery
as normal operation
only state-changing behavior
during recovery
persisted before validation events cannot fail
allows retroactive changes to
the business logic
fixing the business logic will not
affect persisted events
naming: represent intent,
imperative

164. X
Command Sourcing Event Sourcing
write-ahead-log derive events from a command
same behavior during recovery
as normal operation
only state-changing behavior
during recovery
persisted before validation events cannot fail
allows retroactive changes to
the business logic
fixing the business logic will not
affect persisted events
naming: represent intent,
imperative
naming: things that have
completed, verbs in past tense

165. Domain Events
• Things that have completed, facts
• Immutable
• Verbs in past tense
Akka
Persistence
Webinar
• CustomerRelocated
• CargoShipped
• InvoiceSent
“State transitions are an important part of our problem
space and should be modeled within our domain.”
Greg Young, 2008

166. Life beyond Distributed Transactions:
an Apostate’s Opinion
Position Paper by Pat Helland
http://www-­‐db.cs.wisc.edu/cidr/cidr2007/papers/cidr07p15.pdf
“In general, application developers simply do not implement
large scalable applications assuming distributed transactions.”
Pat Helland
Akka
Persistence
Webinar

167. Consistency boundary
• An Actor is can define an Aggregate Root
• Each containing one or more Entities
• Aggregate Root is the Transactional Boundary
• Strong consistency within an Aggregate
• Eventual consistency between Aggregates
• No limit to scalability
Akka
Persistence
Webinar

168. DEMO TIME Persist a game of ping pong

170. http://reactivemanifesto.org

171. Typesafe Activator
http://typesafe.com/platform/getstarted

172. • Purely asynchronous and non-blocking
web frameworks
• No container required, no inherent
bottlenecks in session management
48
Typesafe Reactive Platform
• Actors are asynchronous and
communicate via message passing
• Supervision and clustering in support of
fault tolerance
• Asynchronous and immutable
programming constructs
• Composable abstractions enabling
simpler concurrency and parallelism

173. Reactive is being adopted across
a wide range of industries.

174. 50
Finance Internet/Social Media Mfg/Hardware Government Retail

175. Questions?

176. ©Typesafe 2014 – All Rights Reserved