OpenWSTransaction Enabling Reliable Web Service Transactions

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OpenWS-TransactionEnabling Reliable Web Service
Transactions
Ivan Vasquez Kunal Verma John Miller Amit Sheth
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What is it?

• A middleware framework based on
  WS-Coordination, WS-AT, WS-BA
• Provides fault tolerance
• Minimizes impact to existing Web services
• Application code changes
• Performance

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Actors

• Service composition BPEL
• Context management WS-Coordination
• Transaction management WS-AT/BA
• Participating services
• Conventional services (wrap applications)
• Database back-ends

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Adapting Conventional Web Services
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Coordination and Transaction Management
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Putting it all together
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Demo Normal Conditions

• Process under WS-AT
• Short duration
• Full isolation (close nested transaction)
• Local database transactions commit at the end of
  the transaction protocol
• Sequential, synchronous interactions

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Demo Normal Conditions

• Process under WS-BA
• Potentially long duration
• Partial changes visible (open nested transaction)
• Local database transactions commit immediately
• Compensation to undo preliminary work (delegated)
• Parallel, asynchronous interactions
• Note Operational success ? Logical success

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What can go wrong?

• Logical errors (business logic)
• Handled by
• Business process definition
• Web Services themselves
• Transaction protocols (e.g. 2PC, Business
  Agreement)
• Operational errors (technical failures)
• Process engine
• Coordination service
• Transaction service
• Participants
• Involves hosting servers, database servers,
  network.

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Demo Setup
WS BPEL
Coord.
Flight
Web Client
Hotel
Bank
Tomcat 8080
Tomcat 8088
PgSQL
MySQL
PgSQL
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Participant Failures
WS BPEL
Coord.
Flight
Web Client
Hotel
Bank
X
Tomcat 8080
Tomcat 8088
X
PgSQL
MySQL
PgSQL
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Coordinator Failure
WS BPEL
Coord.
Flight
Web Client
Hotel
Bank
X
Tomcat 8080
Tomcat 8088
PgSQL
MySQL
PgSQL
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Participant Failures (WS-AT)

• Before transaction is decided Understood as a
  negative vote.
• After transaction is decided Problem!
• Logical Logging Track operations on data, rather
  than data itself. Log
• database calls
• parameters
• Scenario
• Transactional process will commit
• Database crashes ? Recover database activity
• Hosting server crashes ? Recover coordination
  context and database activity
• Process resumes normal execution

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Participant Failures (WS-BA)

• No need to recover database activity, however
• Compensation is required
• Coordinator invokes compensating operations based
  on original operation names
• Actual compensation is delegated to Web services
• Scenario
• Transactional process will be canceled
• A service voted to complete
• Its hosting server crashes ? Recover coord.
  context
• Compensate operation
• Process resumes operation

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Coordinator Failure

• Failures leave pending operations at participants
• Coordinator logs transactions, their state and
  participant endpoints (not their outcomes)
• Scenario
• Coordinator goes down amid a transaction
• On restart, recovery process asks participants to
  vote once again
• If a participant is not ready, it is recovered
  too
• Business process can resume execution
• Otherwise, transaction eventually times out and
  cancels all operations

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Adopting the Framework
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(WS-AT only)
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Transactional BPELProcess
Begin
Tx Scope
End
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Future Work

• Provide contingent recovery using related work on
  Web service Autonomic Management
• Integrate with existing transaction managers