Akka.NET Internals: How Akka.Remote Connections Work

@petabridge Petabridge.com

Internals: How Akka.Remote Connections

WorkBy Aaron Stannard

CTO, Petabridge

http://twitter.com/petabridge

http://petabridge.com/



Sample Configuration

akka {actor.provider = "Akka.Remote.RemoteActorRefProvider, Akka.Remote"

remote {helios.tcp {port = 8080

hostname = localhost } }}

akka {actor.provider = "Akka.Remote.RemoteActorRefProvider, Akka.Remote"

remote {helios.tcp {port = 8081

hostname = localhost } }}

System 1

System 2





Terminologies

Akka.RemoteTerms

Transport

Typically a TCPconnection (Helios)

A system can havemultiple active

transports

Endpoint

A specific addressbinding for a

transport

i.e.localhost:8080

Need to have a validtransport for anendpoint to be

enabled

Association

A connectionbetween two

endpoints

Depends on havinga valid inboundendpoint and an

outbound endpoint

AssociationHandle

Interface between anetwork associationand the actors whoreceive messages





Initial State

System 1 System 2

ActorSystem Start ActorSystem Start

Open InboundTCP Endpoint on

Port 8080

Open InboundTCP Endpoint on

Port 8081

Transport listening Transport listening

Wait for incomingassociations

Wait for incomingassociations





Connecting to Remote Systems

akka.tcp://MySystem@localhost:9001/user/actorName1

Protocol

ActorSystem

Address

Path

All parts form an "ActorPath"





Inbound vs. Outbound Endpoints

System 1 System 2

"I want toconnect to you"(OUTBOUND)

"I accept yourconnection"(INBOUND)





Associating

System 1(localhost:8080)


Actor wants to send messageto

akka.tcp://Sys@localhost:8081/user/someActorPath

Open new outbound endpoint

Endpoint on freeport # opened

Send"Handshake"

Message

Receive "Handshake"fromlocalhost:{random}

Accept InboundAssociation

Send "Associate" tolocalhost:{random}

CONNECTIONESTABLISHED





Akka Handshake Protocol

System 1(outbound)

System 2(inbound)

Closed

WaitHandshake

Open

Closed

WaitHandshake

Open

1. User-defined actorwants to send messageto System 2 over TCP

2. No available endpointsto System 2; need to

create new one

Closed

3. Send "Associate"request to System 2

WaitHandshake

Closed

4. Received "Associate"Have we quarantined this node?

WaitHandshake

5. Not quarantined.Send "Associate"back to System 1

Open

WaitHandshake

6. Accept "Associate"from System 2 if not

quarantined

Open

WaitHandshake





Why do we bother?

Establish connection-oriented behavior overany network transport, including connectionlessones likeUDP.





Remoting System Actors

/system

/transports(TransportSupervisor)

/akkaprotocolmanager.{scheme}.{uid}

(AkkaProtocolManager)

/akkaProtocol-{remoteAddress}-{uid}

(ProtocolStateActor)

/endpointManager(EndpointManager)

/reliableEndpointWriter-{url}-{uid}

(ReliableDeliverySupervsior)

/endpointWriter-{url}-{uid}

(EndpointWriter)

/endpointReader-{url}-{uid}

(EndpointReader)

/remote(RemoteDaemon)

/remote-watcher(Remote

DeathWatch)





EndpointManager

EndpointManager

Responsiblefor

Starting alltransports

Applying policiesto each endpoint

Being firstresponder to

inboundassociations

Creates

EndpointWriter

ReliableDeliverySupervisor





Endpoint Policies

EndpointPolicies

Pass OK!

Gated

Node disassociated.

Block all connections to ituntil "retry" window

elapses

Quarantined

Node failed to connectduring association. Mustbe restarted with a new

UID.

Won't establish outboundconnections, but will

accept inbound ifUID isdifferent

Quarantine expires afterwindow of time





Writing to Endpoints

EndpointReader

EndpointWriter

AssociationHandle

MessageDispatcher1. message addressed to remote actor

2. Serialize message & write to handle

3. Writes serialize message to transport





Reading from Endpoints

EndpointReader

EndpointWriter

AssociationHandle

MessageDispatcher

1. Message arrives overnetwork

2. Notifies reader

3.Deserializes &finds recipient

4. Dispatches to recipient





Disassociation



Association

CRASH!

TERMINATED

Transport disconnects

Receive"Disassociation"

notification

Propagate toEndpointManager

Kill all remote deployedactors from System 2;

send all outboundmessages to dead letters





Akka.Remote Training

https://petabridge.com/training/akka-remoting

/

https://petabridge.com/training/akka-remoting/






Akka.NET Internals: How Akka.Remote Connections Work

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