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Transcript of 95-843 Service Oriented Architecture Master of Information System Management Service Oriented...
95-843 Service Oriented ArchitectureMaster of Information System Management
Service Oriented ArchitectureLecture 9
Notes from:Web Services & Contemporary SOA Ch 6, ErlXML Transactions for Web Services, Faheem Khan Distributed Systems Text, Tanenbaum Microsoft Article athttp://msdn2.microsoft.com/en-gb/library/ms996526.aspx
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Today’s Topics
• WS-Coordination
• WS-Atomic Transaction
• Two Phase Commit Protocol
• WS-BusinessActivity
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WS-Coordination
• An OASIS standard
• Developed by IBM, Microsoft & BEA
• Implemented in WebSpehere V6
• Implemented in JBOSS
• Part of MS Vista and the Windows Communication Foundation (Indigo project)
• Apache Foundation Kandula Project
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Coordination
• WS-Coordination includes two lower level standards:
• WS-AT Web Service Atomic Transaction
• WS-BA Web Service Business Activity
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activationService
registrationservice
participant
coordinator
Potential participants
participant
Three services defined by WS-Coordination
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activationService
registrationservice
participant
coordinator
Potential participants
participant
CreateCoordinationContext
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activationService
registrationservice
participant
coordinator
participant
Potentialparticipants
participant
register
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activationService
registrationservice
participant
coordinator
participant
Potential participants
participant
A set of coordination protocol services for each supported coordination type.
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activationService
registrationservice
participant
coordinator
participant
Each coordinatorhas a type: currently either WS-AtomicTransactionor WS-BusinessActivity
This participantwants to engageothers in an atomictransaction.
participant
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activationService
registrationservice
participant
coordinator
participant
1 2
1. 2. Request coordination context.A Coordination Context is an XML document containing:an activity identifier, the type of coordination, a registration endpoint,expiration time and application specific extensibility elements.
Call createCoordinationContext
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Coordination Context <soapenv> <soapbody> <wscoor:CoordinationContext <Identifier> ... </Identifier> <Expires> ... </Expires> <wscoor:CoordinationType> ... </wscoor:CoordinationType> <wscord:RegistrationService> <Address/> </wscoord:RegistrationService> <!--extensibility element ->
</wscoor:CoordinationContext> </soapbody> </soapenv>
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activationService
registrationservice
participant
coordinator
participant
3. 4. Register to play a role in a coordinated activity. The role depends upon what type of activity is going to take place and how the participating application is involved in that activity. The registration service will register the role of the participant application in the activity.
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Call register
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activationService
registrationservice
participant
coordinator
participant
Other players get a copy of the context.
participant
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Players Invited To Play<soapenv> <soapheader> <wscoor:CoordinationContext <wsme:Identifier> http://myCoordinationService/ts/activity1 </wsme:Identifier> <wsme:Expires> 2002-06-30T13:20:00.000-05:00 </wsme:Expires> <wscoor:CoordinationType> http://xml-soap.org/2002/06/AtomicTransaction </wscoor:CoordinationType> <wscoor:RegistrationService> <Address> http://myRegistrationService </Address> </wscoor:RegistrationService> </soapheader> <soapbody> <debitAccount ... /> </soapbody> </soapenv>
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activationService
registrationservice
participant
coordinator
participant
With a copy of the context, other players register.
participant
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1. Sending a CreateCoordinationContext message to the Activation service creates an activity. The optional CurrentContext parameter is absent, so a new activity is created and the returned CoordinationContext has a new activity identifier and Registration service A.
2. The CoordinationContext is propagated from application services A to B as a SOAP header in an application message. This acts as an invitation to application service B to participate in the activity using one of the coordination protocols for that coordination type. The service that receives this invitation can either register to participate or not.
3. Service B registers using the Registration service A from the propagated context. 4. The coordination protocol instance can then begin between the participants. ThisCoordination protocol enables coordination. For example, this may be either the WS-AtomicTransaction 2PC or WS-BusinessActivity protocol.
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WS-Coordination
• The participant application has gained possession of an instance of the coordination context.
• The participant application then propagates the coordination context instance to other applications that it would like to take part in the same activity.
• Those applications also register themselves with the coordinator for the same activity.
• The different participating applications may use the same coordinator or they may want to use their own trusted coordinators. In case different participating applications use their respective coordinators, the coordinators will talk to each other in order to provide coordination services.
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In the above, after the import of the activity or the interposition of the trusted coordinator service B, Application B can deal with its own coordination services, which in turn deals with A's coordination services. 1. Create the activity and receive a CoordinationContext. 2. Propagate A's CoordinationContext to B in an application message. 3. B has a choice of whether to deal directly with A's coordination services, as in our first example, or use another set of coordination services as its representative. It decides to import the activity to B's coordination services by sending its Activation service the CreateCoordinationContext message with the context from A as the optional CurrentContext parameter. The returned CoordinationContext has the same activity identifier, but has B's Registration service. 4. Register B with its own Registration service obtained from its CoordinationContext identifier. 5. B's coordination services delegate the registration to A's Registration service, which it obtained from the CurrentContext parameter during import. This creates a new coordination protocol instance between A and B. 6. The coordination protocol instance can then begin between the participants A and B.
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WS-Coordination
• But what is the coordinated activity (the actual sequence of operations) that will take place?
• WS-Coordination says nothing about the actual activity. It leaves it up to the participating applications to decide what they want to do with the coordination context.
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activationService
registrationservice
participant
coordinator
participant
Suppose everyone is registered for an atomic transaction using 2PC
participant
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Hypothetical Web Service Transaction
Begin transaction BookTrip
book plane
book hotel
book rental car
End transaction BookTrip
Notes adapted from Tanenbaum’s“Distributed Systems Principles and Paradigms”
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activationService
registrationservice
Book TripWS
coordinator
BookPlane WS
Suppose everyone is registered for an atomic transaction using 2PC
Book Car WS
Book Hotel WS
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Transactions (ACID)
• Atomic: All or nothing. No intermediate states are visible.
• Consistent: system invariants preserved, e.g., if there were n dollars in a bank before a transfer transaction then there will be n dollars in the bank after the transfer.
• Isolated: Two transactions do not interfere with each other. They appear as serial executions.
• Durable: The commit causes a permanent change.
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Participant Talks to Coordinator
Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
openTrans Unique Transaction IDTID
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
TID = openTransaction()
Recoverable objects neededto rent a car.
Any server
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Client Calls Methods
BookTrip Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
Call + TID
plane.bookFlight(111,”Seat32A”,TID)
Any server
Recoverable objects neededto rent a car.
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
Plane Joins the Transaction
The participant knows where the coordinator is because that information can be included inthe TID (eg. an IP address.)The coordinator now has a pointer to the participant.
The participant onlycalls join if it has notalready done so.
join(TID,ref to participant)
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
Suppose All Goes Well (1)
OK returned
OK returned
OK returned
Recoverable objects neededto rent a car.
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
Suppose All Goes Well (2)
OK returned
OK returned
OK returned
CloseTransaction(TID) Called
Coordinator begins2PC and this results ina GLOBAL COMMITsent to each participant.
Recoverable objects neededto rent a car.
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
This Time No Cars Available (1)
OK returned
OK returned
NO CARS AVAILabortTransaction(TID) called
Recoverable objects neededto rent a car.
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
This Time No Cars Available (2)
OK returned
OK returned
NO CARS AVAILabortTransaction(TID) called
Coordinator sends a GLOBAL_ABORT to allparticpants
Recoverable objects neededto rent a car.
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
ROLLBACK CHANGES
ROLLBACK CHANGES
This Time No Cars Available (3)
OK returned
OK returned
NO CARS AVAIL abortTransaction(TID)
abortTransaction
Each participantGets a GLOBAL_ABORT
ROLLBACK CHANGES
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
BookPlane Server Crashes After Returning ‘OK’ (1)
OK returned
OK returned
OK returned
Recoverable objects neededto rent a car.
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
Recoverable objects neededto book a hotel.
BookPlane Server Crashes After Returning ‘OK’ (2)
OK returned
OK returned
OK returned
CloseTransaction(TID) Called
Coordinator excutes 2PC:Ask everyone to vote.No news from the BookPlaneParticipant so multicast a GLOBAL ABORT
Recoverable objects neededto rent a car.
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Coordinator
BookPlane Participant
BookHotel Participant
BookRentalCar Participant
Different servers
BookTrip Client
Recoverable objects neededto book a plane
ROLLBACK
BookPlane Server Crashes After Returning ‘OK’ (3)
OK returned
OK returned
OK returned
CloseTransaction(TID) Called
ROLLBACK
GLOBAl ABORT
ROLLBACK
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Two-Phase Commit Protocol - Phase 1
Coordinator
BookPlane
BookHotel
BookRentalCarPhase 1 Coordinator sends a Vote_Request to each process. Each process returns a Vote_Commit or Vote_Abort.
Vote_Request
Vote Request
Vote Request
Vote_Commit
Vote Commit
Vote Commit
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Two-Phase Commit Protocol - Phase 2
Coordinator
BookPlane
BookHotel
BookRentalCarPhase 2 Coordinator checks the votes. If every process votes to commit then so will the coordinator.In that case, it will send a Global_Commit to each process. If any process votes to abort the coordinator sends a GLOBAL_ABORT.Each process waits for a Global_Commit message before committing its part of thetransaction.
Global Commit
ACK
Global Commit
ACK
Global Commit
ACK
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2PC Finite State Machine From Tanenbaum
Init
wait
Abort Commit
Commit----------Vote-request
Vote-commit----------------Global-commit
Vote-abort--------------Global-abort
Init
Ready
AbortCommit
Vote-request-----------------Vote-commit
Vote-request-----------------Vote-abort
Global-commit-------------------ACK
Global-abort----------------ACK
State has already been saved to permanent storage.
Coordinator Participant
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2PC Blocks in Three Places
Init
wait
Abort Commit
Commit----------Vote-request
Vote-commit----------------Global-commit
Vote-abort--------------Global-abort
Init
Ready
AbortCommit
Vote-request-----------------Vote-commit
Vote-request-----------------Vote-abort
Global-commit-------------------ACK
Global-abort----------------ACK
If waiting too long for a Vote-Requestsend a Vote-Abort
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2PC Blocks in Three Places
Init
wait
Abort Commit
Commit----------Vote-request
Vote-commit----------------Global-commit
Vote-abort--------------Global-abort
Init
Ready
AbortCommit
Vote-request-----------------Vote-commit
Vote-request-----------------Vote-abort Global-commit
-------------------ACK
Global-abort----------------ACK
If waiting too long After Vote-requestSend a Global-Abort
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2PC Blocks in Three Places
Init
wait
Abort Commit
Commit----------Vote-request
Vote-commit----------------Global-commit
Vote-abort--------------Global-abort
Init
Ready
AbortCommit
Vote-request-----------------Vote-commit
Vote-request-----------------Vote-abort
Global-commit-------------------ACK
Global-abort----------------ACK
If waiting too long we can’t simply abort! We must waituntil the coordinator recovers. We might also make queries on other participants.
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2PC Blocks in Three Places
Init
wait
Abort Commit
Commit----------Vote-request
Vote-commit----------------Global-commit
Vote-abort--------------Global-abort
Init
Ready
AbortCommit
Vote-request-----------------Vote-commit
Vote-request-----------------Vote-abort
Global-commit-------------------ACK
Global-abort----------------ACK
If this process learns that another has committed then this process is free to commit. The coordinator must have sent out a Global-commit that did not get to this process.
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2PC Blocks in Three Places
Init
wait
Abort Commit
Commit----------Vote-request
Vote-commit----------------Global-commit
Vote-abort--------------Global-abort
Init
Ready
AbortCommit
Vote-request-----------------Vote-commit
Vote-request-----------------Vote-abort
Global-commit-------------------ACK
Global-abort----------------ACK
If this process learns that another has aborted then it too is free to abort.
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2PC Blocks in Three Places
Init
wait
Abort Commit
Commit----------Vote-request
Vote-commit----------------Global-commit
Vote-abort--------------Global-abort
Init
Ready
AbortCommit
Vote-request-----------------Vote-commit
Vote-request-----------------Vote-abort
Global-commit-------------------ACK
Global-abort----------------ACK
Suppose this process learns that another process is still in its init state. The coordinator must havecrashed while multicasting the Vote-request. It’s safe forthis process (and the queried process) to abort.
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2PC Blocks in Three Places
Init
wait
Abort Commit
Commit----------Vote-request
Vote-commit----------------Global-commit
Vote-abort--------------Global-abort
Init
Ready
AbortCommit
Vote-request-----------------Vote-commit
Vote-request-----------------Vote-abort
Global-commit-------------------ACK
Global-abort----------------ACK
Tricky case: If the queried processes are all still in their ready state what do we know? We have to block and wait until theCoordinator recovers.
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Strong Division of Function
• With atomic transactions there is a strong division of function between the business activity and coordination of the transaction.
• The applications decides who to involve in the transaction and whether to commit or abort.
• After this, coordination takes over and decides the outcome.
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Mutual Trust Is Required
• Any system can abort the entire transaction. Systems must be trusted to have cooperative intentions.
• Systems must trust each other to be responsive.
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Business Activity Differs from Atomic Transactions
• Atomic transactions not always appropriate.• May have longer duration (minutes, days,weeks)• Locks should not be held for long periods. • Changes become visible. Say, a process sends
an email. We can’t rollback.• Application logic is involved in the coordination.• Compensation used if parts of a process can’t
complete.