SpringOne 2020 Introducing Saga Pattern in Microservices with Spring Statemachine Omotola Awofolu, Senior Platform Architect/Solution Engineer at VMware

1. Introducing Saga Pattern
with Spring Statemachine
September 2–3, 2020
springone.io
Tola Awofolu

2. Introduction

3. So…what are “sagas”?
And why should you care?...

4. Before we begin…
Some quick definitions
• Sagas
• State Machines
• (More later…)

5. …
5
Complexity of data in modern architecture…
?

6. Ø How state is managed
Ø How state is modeled
6
First up…

7. In the beginning: monolithic applications
7

8. Handling State in Monolithic Architectures
● Centralized Data
● ACID Transactions
● Low degree of essential complexity
● A whole lot is taken for granted
8
-Consistent -Isolated -Durable-Atomic

9. More about Transactions
● Transaction: an atomic unit of work for making
changes to state in a system
● Atomicity
● Concurrency Control
● Consistency Model
● Reliability
● Rollbacks
9

10. Challenge
● Architecture must adapt to evolving needs
● Challenges with Infrastructure
● Challenges with Integration
● Challenges with Data
● Challenges with Modern Use Cases
10

11. Proposed solution…
And then there were microservices!

12. Handling State in Microservice Architectures
● Decentralized Data
● Polyglot Architecture
● Supports distributed and dynamic
environments
12

13. Challenge: More complexity
● Eventual consistency
● Failure detection
● "Lossiness"
● Data completeness
● Event ordering
● Availability/Performance
optimization
13
● Event correlation
● Duplication
● Guaranteed Delivery
● End-to-end fault tolerance
● etc

14. Going back to Transactions…
● Transactions assume a basic consistency
model
● Many degrees of consistency
14
-Causal Consistency
-Read Your Own Writes

15. Consistency Model Trade-offs
● Immediate consistency vs Availability
● Immediate consistency vs Throughput
● Eventual consistency vs Readability
15

16. Implementing Strong Consistency
● With Monolithic systems, we can use ACID
Transactions with ease
● With Distributed systems, we need to support
Distributed Transactions (can sometimes be
ACID based)
● Concurrency Control/Locking Protocol (ex. 2PL)
● Atomic Commit Protocol (ex. 2PC, 3PC)
● Majority Consensus Protocols (ex. Paxos, Raft)
16
(Locking)
(Consensus)
(Consensus)

17. A different approach: Sagas
● “Unit of Work” pattern applied to
microservices
● Saga: Long-running local transaction broken
into separate interleavable transactions
● Distributed Saga: Sequence of transactions
running across multiple decoupled services
● Transactions are ACD (no Isolation)
● Must mitigate against
17
Lost updates Dirty reads Non-repeatable reads

18. How do sagas work?
● Each saga coordinates its local transactions
● When DONE, triggers the next step
● When FAILED/CANCELED, coordinates its
local compensating transactions and triggers
the prior step
18

19. Sagas can use Orchestration or Choreography
● Choreography-based sagas: No centralized
coordinator; participants triggered by
domain events
● Orchestration: Centralized coordinator
responsible for triggering saga participants
19

20. Handling Isolation problem with Sagas
● Semantic Locks
● Commutative Operations
● Optimistic Offline Lock
● Saga Reordering
● Hybrid approach
20
For more information:
excellent book by Chris
Richardson…

21. Ø How state is managed
Ø How state is
modeled
21
Next…

22. There are many patterns for modeling state…
22
State State
State State
State State
State State
Domain Logic Domain Logic Domain Logic
• Conditional/”if/then/else”
logic (spaghetti code)
• State pattern • Truth tables
• Workflow engines
• State Machines
Transition
Transition

23. State Machines: Intro
● State Machines:
● “An abstract machine than can be in
one of a finite number of states at a
time.”
23
Spring
Statemachine

24. Sample: MyFund (Simple Fundraiser APP)
24
PledgeRequested PledgeMatched
PledgeCancelled
[funds>N] / match
/cancel
/cancel
PledgeRequested PledgeMatched
PledgeCancelled
MyFundStateMachine

25. Thank You!
https://www.linkedin.com/in/tola-awofolu-b4a9576/
#springone@s1p
SAMPLE
ARCHITECTURE

26. Thank You!
https://www.linkedin.com/in/tola-awofolu-b4a9576/
GitLab Repo is available at: https://gitlab.com/oawofolu/ssmdemo.git
#springone@s1p