Service Oriented Architecture

1. Service Oriented Architecture A High Level Breakdown for COMP 410 by Dennis Qian Source: SOA with .NET & Windows Azure, Thomas Erl

2. What is Service-Oriented Computing? • New generation of distributed computing platform • Has its own design paradigms, principles, patterns, models, etc. • Creation of solution logic units individually shaped so that they can be collectively and repeatedly utilized

3. Eight Design Principles of service-orientation paradigm Implement a standardized contract Standardized Service Contract Standardized Service Contract Service Loose Coupling Service Abstraction Service Reusability Service Autonomy Service Statelessness Service Discoverability Service Composability Service Loose Coupling Minimize dependencies Service Reusability Implement generic and resusable logic and contract Minimize the availability of meta information Service Abstraction Independent functional boundary and runtime env. Service Autonomy Adaptive and state management-free logic Service Statelessness Service Composability Maximize composability Implement communicative meta information Service Discoverability SERVICE

4. A Service • Container of capabilities associated with a common purpose • Neutral to technology platform • Component – part of a distributed system • Web Service – XML Schema, confusing shit

5. Service Models • Service model – classification indicating type of service based on its logic • Task Service – non-agnostic so general single-purpose, parent business process logic, usually has logic to spawn other services • Entity Service – reusable, agnostic, associates with one or more related business entities • Utility Service – reusable, agnostic, low-level technology-centric functions, not derived from business specifications, notification/logging/security

6. Distributed Computing --> Service Oriented Computing • Computing has moved from procedural programming -> object-oriented programming, and then from OOP -> service-oriented programming • Distributed architecture met evolving demands that client-server architecture was unable to handle, n-tier, service-oriented arch. extends on distributive architecture

7. Service Contracts(basically interfaces for our services) using System; using System.Service Model; namespace HelloWorld { [ServiceContract] public interface IGreetings { [OperationContract] string Greet1(); } } ----- [MessageContract] public class ContractMessage { [MessageHeader] public MsgHeaermsgHeader; [MessageBody] public MsgBodymsgBody ----- <system.serviceModel> <services> <service name=“AccountService”> <endpoint name=“EndPoint1” address=“net.tcp://localhost:1234” binding=“netTcpBinding” contract=“Iaccount” /> </service> </services> </system.serviceModel> Corresponds to ServiceContractattribute Composed of an interface contract and a service endoint Interface Contract – subset of service contract comprised of the operation contract, data contract, and message contract Operation Contract - method or capability as part of interface contract Data Contract – means of expressing data models ie, XML schemas are data contracts Message Contract – pretty much message protocol Service Endpoint – cormprised of address, binding, and contract parts

8. Contract-First approach • Create or Reuse Data Contract • Create Message Contract • Create Interface Contract • allows for standardized service contracts (possibly on industry standards etc.) • Canonical Schemas // XML Schemas // establishes structure and validation rules, can also define data models

9. Data Model Transformation • avoid this shit at run time, which is why we used Standardized Service Contract principle • example: services encapsulating legacy systems inevitably need to transform data between legacy data models and standardized data models • Service B : schema1 -> transform schema -> schema2 : Service A

10. Data Model Transformation • three ways to apply DMT • object-to-object – XML message serialized into object, translated into another object, serialized back into XML • LINQ-XML – irrelevant • XSLT Transformation - irrevenat

11. Canonical Protocol • use the same communication protocol within a service inventory boundary (like TCP for all our module comms) • Dual Protocol – easy because we can just add additional endpoints, allows for primary/secondary protocols say to optimize for performance issues

12. Canonical Expression • obvious but worth mentioning • have uniform naming conventions when it comes to service contract definition • ie. GetOrderStatus() synonymous with RetrieveStatisticsPerOrderMode(), so just be consistent: GetOrderStatus(), GetStatisticsPerOrderStatus()

13. *** Service Loose Coupling *** • goal of this principle is to allow service to develop and evolve with minimal impact on each other

14. Service Loose Coupling • logic-to-contract coupling– internal service logic to service contract, positive, preserves contract’s independence from implementation • contract-to-logic coupling – opposite ^, negative, because changes to logic impact service contract, and consequently also impact service consumers who depend on contract • contract-to-technology coupling– similar ^, negative, forces service consumers to bind to platform-specific technology protocol • contract-to-implementation coupling – negative, directly expressing characteristics of implementation within the contract • contract-to-functional coupling – negative, occurs when general logic is designed with a particular consumer in mind, contract can become dependent on underlying functionality • consumer-to-implementation coupling – negative, consumer bypasses contract to direct access implementation • consumer-to-contract coupling – positive, consumers have limited access to the service contract goal of this principle is to allow service to develop and evolve with minimal impact on each other determines how the contract is architecturally positioned advocates reducing dependencies between service consumers and the service contract, as well as b/w the service contract and the underlying service implementation positive and negative types of coupling

15. underlying service logic is coupled to the service contract consumers are coupled to the service contract SC core service logic service consumers service contract is physically decoupled

16. Service Façade [Service Contract] interface IPersonService { [OperationContract] person GetPerson(intpersonId); } //façade1 class PersonService: IPersonService { public person GetPerson(intpersonId) { return ServiceImplementation. GetPersonById(personId); } } //facade2 class SimplePersonService: IPersonService { public person GetPerson(intpersonId) { var person = ServiceImplementation. GetPersonById(personId); person.address= null; return person; } } class ServiceImplementation { public static person GetPersonById(intpersonId) { return new person{ id = personId }; } } when pursuing logic-to-contract coupling, additional coupling flexibility can be built into the service architecture by establishing additional layers of implementation logic advocates the positioning of a façade components between the contract and core service logic protects the core service logic from changes to the contract, or concurrent contracts typically contains code that: chooses which methods or functions to call in the core implementation compensates for changes in logic to retain coupling allows logic to remain physically separate and stable should contract change

17. façade logic is coupled to core logic façade logic is coupled to contract SC core service logic service façade logic changes to the contract impacts façade logic core logic is decoupled from contract and may therefore not be affected by the change

18. Concurrent Contracts • enables a service to have more than one service contract in order to accommodate different service consumers SC: A service façade logic : A core service logic SC: B service façade logic : B

19. Service Reusability – identification of reusable logic • Separation of Concerns • Functional Decomposition • Service Encapsulation – after above, leads to below • Agnostic Context, single/multi-purpose logic • Agnostic Capabilities

20. Service Composition Service A - Capability A • Aggregate of services composed to automate a particular task • common objective among all SOA design principles (1) (2) (3) (4) (5) • Service D • Capability A • Capability B • Service B • Capability A • Capability B • Service C • Capability A • Capability B

21. Composition Roles • composition controller – service with capability that is executing the parent composition logic required to compose capabilities within other services (CP much?) • composition member – service that participates in a service composition by being composed by another service (FE/Mixers) • composition initiator – program that initiates a service composition by invoking the composition controller, may or may not exist as a service (control panel :D) • composition sub-controller – variation of the composition controller role that is assumed by a service carrying out nested composition logic, within a capability that is composing one or more other service capabilities while itself also being composed (Mixer roles and mixer trees)

22. Service Layers • based on a fundamental separation of agnostic and non-agnostic service logic • end up with a task service layer, followed by agnostic service layers

24. Orchestration • book doesn’t explain it that well, but it’s basically what were doing when we try to construct our cloud tree/graph/chains in an automated way • http://en.wikipedia.org/wiki/Orchestration_%28computing%29 • “Stitching of software and hardware components together to deliver a defined Service” • involves saving state in a State Repository (yeah database)

25. Topics Worth Exploring • Service Bus – basically a big messenger utility to establish comms between services • eventing • service remoting • tunneling • message buffers • service registry • Use of caches – could eliminate some processing • Access Control and cloud security (marketability/extensibility factor)

26. Useful Sites • www.whatissoa.com • www.soaprinciples.com • www.soapatterns.com • www.soa-manifesto.com