Prof.Dr.Dr.h.c.FrankLeymannInstitute ofArchitecture ofApplication Systems

Universitätsstr. 3870569 StuttgartGermany

Phone +49-711-685 88 470Fax +49-711-685 88472e-mail Leymann@

iaas.uni-stuttgart.de

AttheHeartofServices:LooseCouplingandItsArchitecturalBenefits

(WSO2ConnAsia– Colombo,SriLanka– February17th,2016

©FrankLeymann

Agenda

2

LooseCouplingMessagingWS*RESTArchitectural ImplicationsMicroservicesConclusion

©FrankLeymann

Agenda

3

LooseCouplingMessagingWS*RESTArchitectural ImplicationsMicroservicesConclusion

©FrankLeymann 4

T h e M i s s i n g P ie c e s

L o o s e ly C o u p le d

©FrankLeymann

IntegrationProblem:TheOrigin

5

E01-EDI

Data Warehouse(Interfaces to and from theData Warehouse are not

displayed on this diagram)

G02 - GeneralLedger

A05 - AP

S01 - SalesCorrections

I01 POReceiving

I03 Return toVendor

I06 WarehouseManagement

MaininframePC/NT apps Unix apps

3rd Party Interface

S06 - Credit App

P15 EES EmployeeChange Notice

O THER APPS - PCAP - Col l ect i ons/ Credi t

TM - Credi t Card DB

ACCTS REC APPS - PC990CO RBad Debt

Benef i ci al FeesBenef i ci al Reconci l e

JEAXFJEBFAJEBKA

JEDVAJESO AJEVSAJEVSFNSF

Tel eCredi t Fees

I NVENTO RY CO NTRO L APPS - PCCode Al arm

Debi t Recei vi ngsDevo Sal es

Di spl ay I nvent oryI n Home

Junkout sM erchandi se Wi t hdraw al

Promo Credi t sRTV Accrual

Shri nkAP Research - I nv Cnt r lAP Research- Addl Rpt s

Book t o Perpet ual I nvent oryCl ose O ut Report i ng

Comput er I nt el l i gence Dat aCount Correct i ons

Cross Ref f or VCB Dnl dsDamage Wri t e O f f

Debi t Recei vi ngsDFI Vendor Dat abase

Di spl ay I nvent ory Reconci l eDi spl ay I nvent ory Report i ng

I NVENTO RY CO NTRO L APPS - PCDPI / CPI

I C Bat chi ngI nvent ory Adj / Count CorrectI nvent ory Cont rol Report s

I nvent ory Level sI nvent ory Rol l

M erchandi se Wi t hdraw alO pen Recei vi ngsPI Count Resul t s

PI Ti me Resul t s f rom I nvPri ce Prot ect i on

Sal es Fl ash Report i ngShri nk Report i ng

SKU G ross M argi nSKU Shri nk Level Det ai l

USMVCB Dow nl oads

Journal Entry Tool Kit

Scorecard - HR

L02-ResourceScheduling(Campbell)

P09 - P17Cyborg

M02 - Millennium

M03 - Millennium 3.0

Banks - ACH and Pos toPay

Cobra

B01 - StockStatus

S03-Polling

P14 On-line NewHire Entry

CTS

Plan Administrators(401K, PCS, Life ,

Unicare, SolomonSmith Barney)

D01 Post LoadBilling

I04 HomeDeliveries

I02 -Transfers

Arthur Planning

I07 PurchaseOrder

I12 EntertainmentSoftware

I05Inventory Info

E13E3 Interface

S04 - Sales Posting

V01-Price ManagementSystem

I10 Cycle PhysicalInventory

I55 SKUInformation

K02Customer Repair

Tracking I35 Early WarningSystem

B02 MerchandiseAnalysis

I13- AutoReplenishment

U18 - CTO

Intercept

I09 Cycle Counts

E02-EmployeePurchase

Texlon 3.5

ACH

Stock Options

I17 Customer PerceivedIn-Stock

U16-Texlon

SiteSeer

C02 - CapitalProjects

F06 - FixedAssets

US Bank ReconFile

Star Repair

EDICoordinator

M esa Dat a

NEW SoundscanNPD G roup

AI G Warrant y G uard

Resumix

Optika

Store BudgetReporting

P16 - Tally Sheet

Cash Receipts/Credit

S05 - HouseCharges

Ad Expense

L01-PromoAnalysis

V02-PriceMarketing

Support

BMP - Busperformance Mngt

StoreScorecard

I11 PriceTesting

Valley Media

P09Bonus/HR

I15 Hand ScanApps

Roadshow

POS

S08 - VertexSales

Tax

A04 - CustRefund Chks

Equifax

ICMS Credit

CellularRollover

S09 - DigitalSatelliteSystem

NPD,SoundScan

Sterling VANMailbox (Value)

I18SKU Rep

X92-X96Host to AS400

Communication

S02 -Layaways

Washington,RGIS,

Ntl Bus Systems

V04-SignSystem

I14 Count CorrectionsNARM

P01-EmployeeMasterfile

I06 - CustomerOrder

FrickCo

UAR - Universal AccountReconciliation

DepositoryBanks

S07 - CellPhones

S11 - ISPTracking

AAS

Fringe PO

Cash Over/Short

L60 MDFCoop SKU Selection

Tool

SKUPerformance

SupplierCompliance

1

I35 - CEIASIS

Misc Accounting/Finance Apps - PC/NTCOBA (Corp office Budget Assistant)

PCBS(Profit Center Budget System)Merchandising Budget

AIMSMerch Mngr Approval

Batch ForecastingAd Measurement

AIMS Admin

AIMSReportingAd

Launcher

V03- MktReactions

SpecSource

CTO2.Bestbuy.com

RebateTransfer

SignSystem

CopyWriter'sWorkspace

ELTPowerSuite

StoreMonitor

AIS Calendar

Stores & Mrkts

Due Dates

Smart Plus

InsertionsOrders

BudgetAnalysis Tool

Print CostingInvoice App

AIS Reports

BroadcastFilter

Smart PlusLauncher

GeneralMaintenance

Printer PO

PrinterMaintenance

VendorMaintenance

Vendor Setup

Connect 3

Connect 3Reports

Connect 3PDF Transfer

Spec SourceSKU Tracking

S20-SalesPolling

Prodigy

PSP

In-HomeRepair

WarrantyBilling

System

Process Servers(Imaging)

Prepared by M i chel l e M i l ls

ApplicationArchitectureofarealcompanyJ

©FrankLeymann

TightCoupling:LocalMethodCall

Lotofassumptionsbetweencalledandcallingmethod

n Bothmethodsruninsameaddressspacen Bothmethodswritteninsamelanguagen Callingmethodhastopassexpectednumberof

parameters inexpecteddatatypesn Callisimmediate(i.e.synchronous)

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©FrankLeymann

RPC(RemoteProcedureCall)

n AttempttomakeremotecommunicationviaRPCbehavelikelocalcall

n Upside:n Semanticsfamiliartodevelopers

n Downside:n Remote(!)communicationinvalidatesmanyassumptions

localcallsarebasedonn Thus:RPCsimplydoesnot havesemanticsofalocalcall!

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©FrankLeymann

RPC≠LocalCall (1/2)

n Calledmethodmightnotbeavailable(networkfragmentation,serveroutage,...)� TimeDependencyn Howlongshouldcallerwait?

n Remotemethodoftencontrolledbyadifferentparty(businesspartner,...)� FormatDependencyn Whatifsignatureofcalledmethodchanges?

n Rewritecodeofcallingapplication!L

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©FrankLeymann

RPC≠LocalCall (2/2)

n Callingfunctionoftenexplicitlypointstoaparticulartargetfunction� ReferenceDependencyn Whatifcalledfunctionismovedtodifferentmachine?

n Parametershavetomatchmachinearchitecture(little/bigEndian,…), localesettings(codepages,timezones,…)� PlatformDependency

9

©FrankLeymann

Σ =CausesofVolatilityofRPC

n TimeAutonomyviolation≈Allingredientshavetobeavailableatsametime

n FormatAutonomyviolation≈Numberandtypesofparametersmustmatch

n ReferenceAutonomyviolation≈Hard-codedaddresses

n PlatformAutonomyviolation≈Internalrepresentationsofdata(little/bigendian...)

10

©FrankLeymann

Coreprinciple:Reducenumberofassumptionstwopartiesmakeabouteachotherwhentheyexchangeinformation

LooseCoupling

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©FrankLeymann

LooseCoupling:AutonomyAspects

n ReferenceAutonomyn Producersandconsumersdon’tknoweachother

n TimeAutonomyn Producersandconsumersexecuteattheirownpace

n FormatAutonomyn Producersandconsumersmayusedifferentformatsofdata

exchanged

n PlatformAutonomyn Producersandconsumersmaybeindifferentenvironments,written

indifferent languages,…

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Agenda

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LooseCouplingMessagingWS*RESTArchitectural ImplicationsMicroservicesConclusion

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©FrankLeymann

Messaging

15

ApplicationB

�ApplicationA

Endpoint

Message

Channel Route Transform

Manage

©FrankLeymann

ReferenceAutonomyinMessaging

n Producersandconsumerscommunicateviaqueuesortopics,i.e.theydon’tknoweachother

n Routingcomponentsfreeproducersevenfromhavingtoknowwhichqueueortopictousen …i.e.producersonlyhas

tounderstandsinglesourcetosendmessagesto

16

Consumer A

Consumer B

Prod

ucer

©FrankLeymann

TimeAutonomyinMessaging

n Asynchronyisattheheartofmessaging,thustimeautonomyis“initsguts”

n Queuingisproviding1-1connections

n Pubsub isproviding1-nconnections

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SenderReceiver1

Receiverj

Receivern

…

…

Receiver1

Receiverj

Receivern

…

…Sender

©FrankLeymann

PlatformAutonomyinMessaging

n Endpointareisolatingapplicationsfrommessagingenvironment

n Applicationcanbe…n …inanyprogramming

languagen …inanyoperating

environmentn …

n Messagingproductsruninmanyenvironments

n Youcanevenbridgebetweendifferentproducts

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ChannelAdapter EndpointImplement

As…

MessagingMapper

UsesA…

MessagingGateway

ImplementedAs…

MOM 1 MOM 2

©FrankLeymann

FormatAutonomyinMessaging

n Transformationofmessages isdone“onthewire”n Versioningofmessages isenabledn …

19

ATranslator

B

Translator

A

B

Translator

Translator

CanonicalData Model

TranslatorC C

Translator Translator

� �

��

� � �

©FrankLeymann

Agenda

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LooseCouplingMessagingWS*RESTArchitectural ImplicationsMicroservicesConclusion

©FrankLeymann 21

©FrankLeymann

MessageEndpoints

n Applicationstypicallydonotsenddatatoorreceivedatafromachanneln Theyarenot builtwithintegrationinmind!

n Messageendpoints connectapplicationstointegrationsolution

22

A

Endp

oint

AEndpoint B

B

M M’

©FrankLeymann

CharacteristicsofaMessagingEndpoint

23

FunctionImplementation

FunctionImplementation

…isatanaddress

…isreachableviacertaintransports&messageencodings

…implementsaninterface

MessageEndpoint

Port TypePort

Binding

WSDL

©FrankLeymann

ProtocolsareChangingAlongAPath

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InitialSender

UltimateReceiver

MyGateway Firewall Your

Gateway

� Ingeneral,youcannot relyonanyQoS of„the“transportprotocol

Message path

Enterprise1Enterprise2

JMS

HTTP

RMI/IIOP

MQ

©FrankLeymann

SOAP

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Intended forultimate receiver

SOAP Envelope

SOAP Header

SOAP Body

Header Block H1

Header Block Hn

Body Sub-element B1

Body Sub-element Bk

...

...Intended forintermediaries

Payload formiddlewareensuring QoS

Payload forapplication

©FrankLeymann

LooseCouplinginWS*

n ReferenceAutonomyn Clientinteractswithanendpoint(oftenaURI)notwitha

concreteprogram,i.e.clientdoesn’tknowtheactualservicen TimeAutonomy

n Asynchronousbindings(JMS,…)canbeusedn Reply-toheader,Correlationheader,…supportasynchrony

evenoversynchronoustransportsn PlatformAutonomy

n Clientinteractswithservicewithouthavingtoknowprogramminglanguage,hostingenvironment,…ofservice

n FormatAutonomyn Bindingspecifiesserializationformatn Transformationcanbedone“invisibly”alongthewire

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Agenda

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LooseCouplingMessagingWS*RESTArchitectural ImplicationsMicroservicesConclusion

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©FrankLeymann

CoreIdeaBehindREST

n RESTisanarchitecturalstyle,notatechnology

n ItallowstoapplytheWebArchitecturetomoresophisticatedinteractions

n KeyPoints:n REpresentationaln StateTransfer

©FrankLeymann

CharacteristicsOfTheWebArchitecture

n InteractionwithURIaddressableresourcesn Fixedsetofgenericinteractions

(mainlyHTTPGET,POST,PUT,andDELETE)n Standarddataformat(HTML,XML,…- MIMEtypes)n Stateless

n Allcontextisfullyunderstandablefrommessage

©FrankLeymann

ReferenceAutonomyinREST:URIs

n URIdecouplesfromknowingtheactualfunctionimplementation

n HATEOASgoesbeyond(seelater)

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ResourceImplementation

ResourceImplementation

Resource

Resource

URIClient

REST Server

©FrankLeymann

TimeAutonomyinREST:LongRunningRequests

n Sometimesrequestsmaytaketoolongforaclienttowaitforresponsen EspeciallyPOST andDELETEmaytakesometime

n Theymightinitiateacompletebusinessprocesses

n Serveracknowledgesreceptionofrequestn ViaHTTPStatusCode202 Accepted

n Serverprovidesaresourcethatclientcanusetotrackprogressoflong-runningrequest(aka“task”)n ViaContent-Location headerofthisresource,orn ViaLink tothisresource

©FrankLeymann

Example:StartingLongRunningRequest

POST /imageProcessing/beautify HTTP/1.1Host: www.fl.comContent-Type: multipart/related; boundary=fl42

--fl42...--fl42...--fl42--

HTTP/1.1 202 AcceptedContent-Type: application/xmlContent-Location: http://www.fl.com/imageProcessing/tasks/1

<status><state>running</state><link rel="self" href=".../tasks/1"/><estimatedCompletion>2020-04-01</estimatedCompletion>

</status> Task

Res

ourc

e

©FrankLeymann

Example:CheckingStateofLongRunningRequest

GET /imageProcessing/tasks/1 HTTP/1.1Host: www.fl.com

HTTP/1.1 200 OKContent-Type: application/xmlContent-Location: http://www.fl.com/imageProcessing/tasks/1

<status><state>running</state><link rel="self" href=".../tasks/1"/><estimatedCompletion>2020-10-10</estimatedCompletion>

</status>

©FrankLeymann

Example:CompletionofLongRunningRequest

n Location headerpointstonewlycreated,i.e.successfullyprocessedresourcebutnottothetaskresource

n Content-Location header(still)pointstothetaskresource

GET /imageProcessing/tasks/1 HTTP/1.1Host: www.fl.com

HTTP/1.1 303 See OtherContent-Type: application/xmlLocation: http://www.fl.com/images/314Content-Location: http://www.fl.com/imageProcessing/tasks/1

<status><state>ready</state><link rel="self" href=".../tasks/1"/><message>Image processed & stored</message>

</status>

©FrankLeymann

Example:FailedLongRunningRequest

GET /imageProcessing/tasks/1 HTTP/1.1Host: www.fl.com

HTTP/1.1 200 OKContent-Type: application/xmlContent-Location: http://www.fl.com/imageProcessing/tasks/1

<status><state>failed</state><link rel="self" href=".../tasks/1"/><message>Image could not be processed</message>

</status>

©FrankLeymann

PlatformAutonomyinREST

n ThepremiertransporttoimplementRESTisHTTP(S)

n HTTPclientsandHTTPserversareavailableinallmajorenvironments

n Programsinmostlanguagescanbeproducers andconsumersofHTTPmessages

37

©FrankLeymann

FormatAutonomyinREST:ContentNegotiation

n Often,requestedentityisavailableinmultiplevariants

n HTTPdefinesprocedures tonegotiatetheappropriatevarianttobetransferred

38

Client Server

VariantEntity

VariantVariantVariant

Selection

Response

Request

©FrankLeymann

ReferenceAutonomy:HATEOAS

n HATEOAS=HypermediaAsTheEngineOfApplicationState

n Theserverreturnslinks(“hypermedia”)thatdescribethefunctionsvalidintheactual“state”ofthe“application”

39

©FrankLeymann

Example:ReturningApplicableFunctions

GET /orders/42 HTTP/1.1Host: www.fl.com

HTTP/1.1 200 OKContent-Type: application/xml

<order><customer>Frank</customer>...

<link href="www.fl.com/cancellations/42" rel="www.rels.com/orderAPI/POST/cancel"/>

<link href="www.fl.com/ShipDetails/42" rel="www.rels.com/orderAPI/GET/shipping"/>

</order

©FrankLeymann

RESTMaturityModel(akaRichardsonMaturityModel)

n SupportofHATEOAS

n UseofappropriateHTTPmethodstomanipulateindividualresources

n UseofappropriateHTTPstatuscodesandheaderfields

n Individualresourcesareidentifiedn Useofsinglemethod(typicallyPOST)n Methodinvokedonindividualresourcen Similarto“objects”

n HTTPisusedasatransportonlyn Singleentrypointonlyn Useofsinglemethod(typicallyPOST)n Examples:SOAP,XML-RPC

SwampofPOX

Resources

HTTPVerbs

HypermediaControls

Level0

Level1

Level2

Level3

©FrankLeymann

RESTWSvs “Big”WS

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©FrankLeymann

Agenda

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LooseCouplingMessagingWS*RESTArchitectural ImplicationsMicroservicesConclusion

©FrankLeymann

TwoClassesofFaults

n Afault isaneventwithinasystemthatcausedafailure

n Transient faultdoesnotre-occurwhenretryingtheoperation(“Heisenbug”)

n Permanent faultisrepeatable(“Bohrbug”)

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©FrankLeymann

FixingFaults

IfsoftwarefaultisaBohrbug thereisnorepair:

n Getanemergencyfixorwaitforthenextrelease

IfsoftwarefaultisaHeisenbug thenrepairiseasy:

→Shutdownandrestart

Luckily,mostsoftware-caused faultsareHeisenbugs

45

©FrankLeymann

Fail-FastTechniques:Watchdog

Awatchdog isaspecialprogramthatdetectsfaultsofapplicationcomponents fast

Itdoessoby…

n Monitoringtheliveness ofthesecomponents, and

n Re-creatingfailedcomponents “immediately”

…whichisequivalenttoshutdownandretryJ

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©FrankLeymann

Watchdogs:Fault-DetectionMonitoring

47

App

App

App

App

Watchdog

?N=?

App

App

App

App

QueueCardinality LockAcquisition

Pulse Heartbeat

©FrankLeymann

Hot-Pooling:HighAvailability

n HotPool:n Acollectionofapplicationcomponentswithidenticalfunctionality

sharingacommoninputqueuen Whenamemberfailstheothermemberswillcontinue

processingrequestsfrominputqueue� Availabilityn Watchdogwillrestartfailedmembers� HighAvailability

48

ServerServer

ServerClient AppPUT

GET

HotPool

Update

Watchdog

=Shutdown&Retry

©FrankLeymann

ABitofMath:ForgiveMeJ

49

αhot pool = P≥1 = i

N( )i=1

N

∑ α i 1−α( )N−i

= iN( )

i=0

N

∑ α i 1−α( )N−i− N

0⎛

⎝⎜⎞

⎠⎟α 0 1−α( )N⎛

⎝⎜

⎞

⎠⎟

= α + 1−α( )( )N− 1−α( )N

…alotofexplanations,e.g.applicationcomponentsfailindependently;independenteventsare“binomialdistributed”;availabilitymeansthatatleastonememberisrunninginhotpool;etc etc…

αhot pool = 1− 1−αmember( )N�

Example:Assumeaterriblybadapplicationcomponentwith80%availability(αmember=0.8).

Hotpoolwith8ofsuchbadcomponentshas99.999availability(αhotpool=0.99999)!

©FrankLeymann

Hot-Pooling:Scalability

n WatchdogcanmonitormetricsofSLOsofhotpooln IfSLOsarethreatenedtobenotmet,watchdogwillstart

additionalmembers� Scale-outn Ifmembersareunderused,watchdogwillshutdownsubsetof

members� Scale-in

50

ServerServer

AppGET

Watchdog

ServerServer

ServerAppGET

Watchdog

Scale-out

ServerAppGET

WatchdogScale-in

©FrankLeymann

UnderlyingHotPools…

51

…isloosecoupling!

ServerServer

ServerClient AppPUT

GET

Update

©FrankLeymann

n AnApplicationSystem isthecomplete,interdependentsetofhardware,middleware,applications,...requiredtoprocesscompletebusinessrequests

C1 C2 Cn…

ApplicationSystem

ApplicationSystems

52

©FrankLeymann

Stability

n Anapplicationsystem(orsystemforshort)iscalledstableiff itkeepsprocessingbusinessrequestsevenwhentherearetransientimpulses,persistentstresses,orcomponentfailuresdisruptingnormalprocessing

n Animpulse isarapidshocktoasystemn It'slikewhackingthesystemwithahammer

n Stress islikeaforcebeingappliedtoasystemoveranextendedperiodoftime

n It'slikeconstantlypushingagainstthesystem

53

©FrankLeymann

n 100.000newsessionswithinaminuteisanimpulsen 8.000.000newmessagesinaqueuewithinafewminutes

beforeclose-of-businessisanimpulse

n Suchanimpulsecanbreakasystemwithinseconds!

ImpulseinSoftware

54

©FrankLeymann

n Slowresponsefromyourcreditcardprocessoroveralongperiodoftime (see next)isstress

n ...becauseitreducesthecapacitytoservecustomers

Stressproducesstrain

n Stressfromthecreditcardprocessorproducesstrainthatpropagatetootherpartsofthesystem

n ...resultinginrequestspilingupinqueues,queuesgettingfull,refusingnewrequests,stoppingservicestocustomers

StressinSoftware

55

©FrankLeymann

n Howlongisa"longperiodoftime"?

Itdepends!

n Averygooddefinitionisthetimebetweentwocodedeployments

n Ifyoudeployyoursystemonceaweekitdoesn'tmattertobuildthesystemtorunforfiveyearswithoutinterrupt

LongPeriodofTime

56

©FrankLeymann

n Suddenimpulsesandexcessivestraincanbothtriggercatastrophicfailure!

n Analogy:asteelplatewithamicroscopiccrackinthemetal.Understressthecrackcanbegintopropagatefasterandfasteruntiltheplatebrakes!

Cracks

57

©FrankLeymann

n Example:automotiveengineersbuildcrumplezonesintothecarbodytoprotectpassengersbyfailingfirst

n Similarly,buildyourcomponentstostopcrackspropagatingintotherestofthesystem

Design forfailure!

CrackStoppers

58

©FrankLeymann

n ...amplificationistypicallydonebytightcoupling:tightcouplingacceleratescracks

Looselycoupledcomponentsactasshockabsorber,diminishingeffectsoferrorsinsteadofamplifyingthem

TheRoleofLooseCoupling

59

©FrankLeymann

HowtoCopewithCracks

n ThemostimportanttechniquetoavoidcracksistheCircuitBreakern Buttherearemanyothertechniques:

seethebookbyMichaelT.Nygard

n However:

n Thus:

60

Designforfailure!

CracksWILLHAPPEN!

©FrankLeymann

IntermediateConclusion

61

Loosecoupling(especiallytimeautonomyandreferenceautonomy≈reliablemessaging)

supportsbuildinghighlyavailable,scalableandstablecomponents

inastraightforwardmanner

©FrankLeymann

Agenda

62

LooseCouplingMessagingWS*RESTArchitectural ImplicationsMicroservicesConclusion

©FrankLeymann 63

©FrankLeymann

Definition:Quote(*)

n …microservice architectural style isanapproachton developingasingleapplicationasasuiteofsmallservices,n eachrunninginitsownprocessandn communicatingwithlightweightmechanisms,oftenanHTTP

resourceAPI.n Theseservicesarebuilt

n aroundbusinesscapabilitiesandn independentlydeployablebyfullyautomateddeployment

machinery.n Thereisabareminimumofcentralizedmanagementof

theseservices,whichn maybewrittenindifferentprogramminglanguagesandn usedifferentdatastoragetechnologies.

64

(*) J.Lewis&M.Fowler:“Microservices”(2015),http://martinfowler.com/articles/microservices.html

©FrankLeymann

Microservice:MainProperties

Microservice isn smalln runninginitsownprocessn communicatingoften[via]HTTPn builtaroundbusinesscapabilitiesn writtenindifferentprogramming

languagesn usedifferentdatastorage

technologiesn independentlydeployableby

fullyautomateddeploymentmachinery

65

…what everthatmeansL

Trueformany(!)service

Trueformany(!)service,andmostRESTservices

That’swhatservicesareallabout!

That’sinterestingJ

container

©FrankLeymann

Microservice:TheEssence?

66

Amicroservice isaservicethatisindependently deployable

byfullyautomateddeploymentmachinery

…andthishasinterestingimplications(seenext)

©FrankLeymann

AProblem

n Youhavea“bigapplication”(a.k.a.“monolith”)n Ifyouwanttoreplicate it

n …e.g.becauseofscale,availability,elasticity,…

youpaypenalties(e.g.licensesforallcomponents)althoughyouonlyneed“afewcomponents”replicated

67

Application

…Sca

le,

HA,…

©FrankLeymann

Solution

n Splityour“bigapplication”into“smaller”granulesthatcanbedeployedindependentlyn I.e.splititintomicroservices

n Replicationcanberestrictedtothosecomponentsthatturnouttobebottlenecks(� scale),critical(� HA),…withoutpayingthepenaltiesforallothercomponentsofthe“bigapplication”

68

Application

©FrankLeymann

TheEssenceofMicroservices

n Microservicesareallabout…n …propergranularityofcomponentsn …independentdeployment

n Theyarenotacounter-proposal toSOAn Theydonot provethatSOAfailed

n Intheopposite:theyrequireloosecoupling,…n Theyrequireamethodologytodetermine“proper

granules”forcomponentsn …somethingliketheholygrailofsoftwareengineeringfor

decades!n …so,don’texpectyourmiddlewarevendorstosolvethis

problemforyou!It’sallaboutYOUsolvinganverydifficultarchitecture/designproblem!!!

69

©FrankLeymann 70

©FrankLeymann

IDEALPrinciple:NativeCloudApplicationProperties- ArchitectsView

Distribution:decomposed application to……usemultiple cloud resources…support thefactthatclouds arelargeglobally distributed systems

Elasticity:build application tosupport scaled-out and scaled-in dynamicallyScale out:acquire additional resources tosatisfy growingworkloadScale in:freeup resources ifworkload shrinks

? LooseCoupling:influence of application components has tobe limitedExample: failures should not impact other componentsExample: addition /removal ofcomponents issimplified

IsolatedState:build theapplication stateless with respect to…Session State:stateofthe communication with theapplication

AutomatedManagement: runtime management should be handled quickly ,automaticExample: automatic license acquisition because ofuse of additional resourcesExample: resiliency by reacting toresource failures

©FrankLeymann

CloudComputingPatterns:Overview

Applica on Workloads

Cloud Service Models & Cloud Deployment Types Cloud Environments Processing Offerings Communica on Offerings Storage Offerings

Applica on Management

Cloud Integra onMul -TenancyFundamental Architecture StylesNa ve Cloud Applica onsHybrid Cloud Applica ons

Applica on Components

Cloud Run meEnvironment

Cloud Applica on

User GroupLoad

Balancer

Presenta on MessageQueue Business Logic Data

OperaƟonManagement

Processing

......

CommunicaƟon Storage

1 2 3

StaƟcWorkload(25)PeriodicWorkload(28)

Once-in-a-lifeƟmeWorkload(31)UnpredictableWorkload(33)ConƟnuously Changing Workload(36)

Infrastructureas a Service(41)Plaƞormas a Service(44)SoŌwareas a Service(49)

PublicCloud(56)PrivateCloud(59)CommunityCloud(64)Hybrid Cloud(67)

ElasƟcInfrastructure(78)ElasƟcPlaƞorm(81)Node-basedAvailability(85)Environment-basedAvailability(88)

Hypervisor(91)

ExecuƟonEnvironment(94)

VirtualNetworking(118)Message-orientedMiddleware(122)Exaclty-onceDelivery(126)

At-least-onceDelivery(128)TransacƟon-basedDelivery(130)Timeout-basedDelviery(132)

Two-ƟerCloud ApplicaƟon(259)Three-ƟerCloud ApplicaƟon(263)Content DistribuƟonNetwork(268)

HybridUser Interface(271)HybridProcessing(274)

HybridData(277)HybridBackup(280)Hybrid Backend(282)Hybrid ApplicaƟon FuncƟons(285)

Hybrid MulƟmediaWeb ApplicaƟon(287)Hybrid Develop-ment Environment(289)

ProviderAdapter(216)ManagedConfiguraƟon(219)ElasƟcityManager(221)ElasƟcLoad Balancer(224)ElasƟcQueue(227)

Watchdog(230)

ElasƟcity Man-agement Process(237)Feature Flags Man- agement Process(240)Update TransiƟonProcess(245)Standby PoolingProcess(248)Resiliency Man-agement Process(252)

SharedComponent(188)

Tenant-isolatedComponent(191)

DedicatedComponent(195)

Restricted Data AccessComponent(198)Message Mover(201)ApplicaƟon ComponentProxy(203)Compliant DataReplicaƟon(205)

StatefulComponent(150)StatelessComponent(153)MulƟ ComponentImage(184)

User InterfaceComponent(156)

ProcessingComponent(160)Batch ProcessingComponent(165)

IdempotentProcessor(176)

TransacƟon-basedProcessor(179)Timeout-basedMessage Processor(182)

Data AccessComponent(168)DataAbstractor(173)

Map Reduce(96)

=1

1+

StrictConsistency(110)EventualConsistency(113)

Key-valueStorage(107)

ID

BlobStorage(101)

BlockStorage(100)

1.1 1.2

ZZZ

IntegraƟonProvider(208)

DistributedApplicaƟon(143)

LooseCoupling(139)

?

1+

RelaƟonalDatabase(103)

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©FrankLeymann

Agenda

73

LooseCouplingMessagingWS*RESTArchitectural ImplicationsMicroservicesConclusion

©FrankLeymann

Summary

n Buildingrobustapplicationsisallaboutproperarchitecture anddesign

n Loose-Couplingisacentralprincipleofsucharchitectureanddesign

n Loose-Couplingissupportedbythemainstreamservicetechnologies

n Thereisnomiddlewareortoolingmagicthatensuresbuilding“good”service-basedsystems!

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Butit’sallaboutYOUapplyinggoodarchitecturalprinciples

(likeloosecouplingJ)

©FrankLeymann

Thanksforyourattention!

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