This presentation outlines a specification for managing transactions across microservices

1. Senior Director - Platform Architecture,
WSO2
Managing Transactions in Your
Microservices Architecture
Afkham Azeez

2. What is a distributed transaction?
ORACLE
M
MySQL
M
Oracle DB
Instance
MySQL DB
Instance
Queue
Remove Message
Insert Record
Insert Record
Resource ManagersGlobal Transaction

3. Why do we need it?
Debit $1000
FROM Jack’s
Account
Start Start
Success Success
Success Failed
Transaction
Boundary
Debit $1000
FROM Jack’s
Account
Credit $1000
TO Tom’s
Account
Credit $1000
TO Tom’s
Account
Transaction
Complete
We are in
Trouble
Action: Jack’s doing a bank
transfer of $1000 from his
account to Tom’s

4. Monolith - multiple modules in the
same process
Microservices - modules running in different
processes
The problem

5. Transactions in monoliths
Monolith
C3
C1
C2
txn
txn

6. Transactions in microservices
Microservices
C3C1
C2
txn txn

7. Transactions in microservices
µ3
µ1 µ6
µ2 µ4
µ5

8. Joint outcome based on an orchestrator
F
E
C
B
A
D
Orchestrator
µ1 µ2 µ5µ3 µ4 µ6

9. Joint outcome
based on
coordination

10. Sphere of control
µ3
µ1 µ6
µ2 µ4
µ5
Initiator
Participants
Tying together microservices as a unit
S1
S2
S3

11. (1)Start
(2)Context
Infection
µ3
µ1
µ6
µ2 µ4
µ5
Coordinator
(4) Register
(3) Request & Context
Mechanism used to extend the sphere of control

12. Agreement protocols & coordination types
● Joint outcome is negotiated at the end of interactions
● Negotiation rules and how to determine outcome is referred
to as an agreement protocol
● Collection of agreement protocols is called a coordination
type

13. Enabling an agreement protocol
Coordinator’s
Protocol
Endpoint
Coordinator’s
Registration
Endpoint
…
Register-at
Coordination-type
...
µ’s
Protocol
Endpoint
µ
(3) Response( )
(2) Register(Protocol, )
(1)
Context

14. Coordination types
● 2 phase commit (2PC)
● Compensation

15. 2PC Coordination

16. 2PC Coordination Protocols
● Completion
○ Used by participants that control the end of a transaction by an
explicit commit or abort command
● Durable
○ Used by participants that manipulate persistent resources
● Volatile
○ Used by participants that only need to get a notification that the
voting phase of the 2PC has started
○ e.g. microservices that cache data which need to flush data before
transaction ends

17. Commands

18. Create Context
Micro-Transaction-Context:
Micro-Transaction-Context-Version: <version number>
Micro-Transaction-Identifier: <globally unique identifier>
Name-of-Coordination-Type: 2PC | Compensation | ...
Register-At: <uri>
create-context(in: Name-of-Coordination-Type,
out: Micro-Transaction-Context?,
fault: Invalid-Coordination-Type? )

19. Register
register(in: Micro-Transaction-Registration,
out: Micro-Transaction-Coordination?,
fault: ( Invalid-Protocol |
Already-Registered |
Cannot-Register |
Micro-Transaction-Unknown )?
)
Micro-Transaction-Registration:
Micro-Transaction-Identifier: <globally unique identifier>
Protocol: ( Completion | Durable | Volatile | ... )+
Participant-Protocol-At: <uri>+

20. Commit - by initiator
commit(in : Micro-Transaction-Identifier,
out : ( Committed | Aborted | Mixed )?,
fault: ( Micro-Transaction-Unknown | Hazard-Outcome )?
)

21. Abort - by initiator
abort(in : Micro-Transaction-Identifier,
out : ( Aborted | Mixed )?,
fault: ( Micro-Transaction-Unknown | Hazard-Outcome )?
)

22. Prepare (participants)
prepare(in: Micro-Transaction-Identifier,
out: ( Prepared |
Read-Only |
Aborted |
Committed )?
fault: ( Micro-Transaction-Unknown | Prepare-Failed )? )

23. Notify (participants)
notify(in: Micro-Transaction-Identifier,
in: ( Commit | Abort )
out: ( Committed | Aborted )?
fault: ( Not-Prepared | Micro-Transaction-Unknown | Failed-EOT )?
)

24. 2PC coordination
Completion protocol
alt
Initiator Coordinator
Create-Context()
Micro-Transaction-Context
Commit()
Committed | Aborted | Mixed
Abort()
Aborted | Mixed

25. 2PC coordination
Durable protocol - triggered by commit
success
Coordinator Participant
Prepare()
Prepared | Read-Only | Aborted | Committed
notify(...Commit...)
Committed
notify(...Abort...)
Aborted

26. 2PC coordination
Durable protocol - triggered by abort
Coordinator Participant
notify(...Abort...)
Aborted

27. ● A coordination type
● Participant will register compensation endpoint with
coordinator
● Compensations pairs
○ Endpoints which can participate in transactions will declare
compensation actions
Compensation

28. Transactions sidecar
Bridging to existing runtime transactions
Spring Boot
Participant
Txn Sidecar
Initiator
Participant
Participant
Spring Txn

29. service<http:Service> InitiatorService bind listener {
hiInitiator (endpoint caller, http:Request req) {
// This is how you initiate a transaction
transaction with retries =2 {
// Calling a remote participant
http:Response res =
check participant->get(“/ParticipantService/hi”)
} onretry {
// Code here will execute before retrying
} committed {
// Code here will execute after the initiated transaction
// has committed
} aborted {
// Code here will execute after the initiated transaction
// has been aborted
}
}
Ballerina example
Initiator

30. service<http:Service> ParticipantService bind listener {
@transactions:participant {
oncommit = onTxnCommit,
onabort = onTxnAbort
}
hi(endpoint caller, http:Request req) {
// Transactional code goes here. If there are transaction
// aware stuff such as SQL connectors etc. they will
// be registered as resources affected by this transaction
// This local function call on the remote participant will
// result in the function registering with the initiator
// as a remote participant
remoteParticipantDoSomething();
}
}
Ballerina example
Participant

31. Demo

32. THANK YOU
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