Managing complex business transactions
Dariusz Pawlukiewicz
19.12.2018, bstoknet #88
in distributed world of micorservices...
Example CBT
CBT in monolith
The issue in DShop
...Mircorservices
- domain is distributed into several services
- async protocol for writes (queue). Possible LLT.
- the whole app was pretty much done. Had to fit into Event-Driven Architecture.
Why was it an issue?
- ability to support distributed business transactions
- ability to inform end-user about DT state
What we wanted to achieve?
2PC - Two phase commit
2PC - Request Commit
Coordinator
Flights
service
Hotels
service
Cars
service
Request
& Lock
2PC - Verdict - NO
Coordinator
Flights
service
Hotels
service
Cars
service
NO
YES
UNLOCK
2PC - Verdict - YES
Coordinator
Flights
service
Hotels
service
Cars
service
YES
COMMIT & UNLOCK
DEMO
2PC Summary
- Easy to understand
- Centralized distributed transaction management
- "Immediate" result for end-user
- Requires extra code
- Based on sync protocol (HTTP)
- Slow - depends on nodes response time
- Blocking resources
Event Choreography
Event choreography
API
Flights
service
Hotels
service
Cars
service
(C) Book flight
(E) Flight booked
(E) Hotel booked
(E) Car rental rejected
DEMO
Event Choreogrpahy Summary
- Easy to understand
- Almost no extra code required
- Fits into Event-driven architecture
- Based on async protocol
- No centralized distributed transaction management
- May cause spaghetti dependecies -> hard to follow
- Not so easy to test
API
Flights
service
(C) Book flight
Operations
service
(C) Book flight
SignalR service
(E) Operation updated
(E) Flight booked
(WS) Operation updated
How to determine operation status?
Saga pattern... wait what?
Process manager
Saga pattern
- No state machine
- No persisted data
- Designed for failure compensating
- State machine
- Persisted data
- Designed for managing processes
Saga pattern
API
Flights
service
Hotels
service
Cars
service
(C) Book flight
(E) Flight booked
(E) Hotel booked
(E) Car rental rejected
Saga
(C) Book hotel
(C) Rent car
Compensate
.NET Core Saga frameworks
- Worfklow-core
- NServiceBus Saga
Chronicle
Process manager/saga pattern framework for .NET Core
DEMO IN DSHOP
Saga pattern (sort of) Summary
- Easy to understand
- Centralized distributed transaction management
- Fits into Event-driven architecture
- Based on async protocol
- Required some extra work
Which approach is the best?
AVOIDING distributed transactions
BEST:
Event Choreography
SIMPLE TRACKING:
Process manager/Saga
IF NECESSARY:
Bunch of links
- Demos - bit.ly/2ORQmhg
- DShop - bit.ly/2Q3HLIg
- Chronicle - bit.ly/2Qab387
- NserviceBus Saga - bit.ly/1fZFQSk
- Devmentors.io
Thanks!
@d_pawlukiewicz
foreverframe.net
O złożonych procesach biznesowych w rozproszonym świecie mikrousług
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