Ultimamente ci hanno stressato come non mai che stateful è il male. Tutto deve essere stateless, altrimenti non scala, non può essere altamente disponibile, ed è complesso da manutenere ed evolvere. Nonostante questo i sistemi software complessi, essendo basati su processi collaborativi, sono per natura stateful. I processi collaborativi, noti anche come long running business transactions, necessitano di interagiscono con risorse distribuite. L’approccio tradizionale basato su transazioni distribuite, anche se allettante, è una bomba pronta ad esplodere. Pane quotidiano per le Saghe. Le Saghe consentono di modellare sistemi complessi senza la necessità di transazioni distribuite e coordinamento esterno. Vedremo cosa sono le Saghe, come possono essere usate per modellare domini complessi, e che ruolo giocano quando progettiamo sistemi basati sui concetti di “design for failures” e “eventual consistency” (It’s all right, I know where you’ve been)

1. #XeOneDay
Evento realizzato
grazie al supporto di

2. welcome to the
(state) machine
It’s all right, I know where you’ve been
mauroservienti
Mauro Servienti

3. All I want to do when I wake up in
the morning is…
(cit. Rosanna, Toto, Toto IV)
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4. mauroservienti

5. buy ticket(s)
stage dive… :-)
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6. All what they want to do is…
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7. mauroservienti

8. display available tickets
reserve ticket(s)
charge my credit card
deal with insurance
ship ticket(s)
deal with their stuff
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9. sometimes order doesn’t matter
sometimes it does!
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10. Process Manager
Connecting the dots…
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11. Tickets Selection
Credit Card
Gateway/ACL
Orders Manager
Checkout request
AuthorizeCard
request/response
Reservation
Gateway/ACL
ConfirmTickets
request/response
Credit Card
Gateway/ACL
ChargeCard
request/response
Insurance
Gateway/ACL
TicketsInsurance
request/response
Shipping
Gateway/ACL
Shiptickets
request/response
2-phase commit (kind-of)
…
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Reservation
Gateway/ACL
SelectTickets
request/response

12. Process Manager (a different point of view)
New requirement: collect tickets at the venue
OrderId ShippingId ShippingStatus Etc
12 1337 Delivered …
58 1338 Pending …
Orders table
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13. mauroservienti
like a Punch Card, a Process Manager owns the process

14. Ticket(s)
Stuff…
Insurance
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15. Process Managers, a source of coupling
•Violates Single Responsibility Principle
•Contention/Performance Bottleneck
•Conflicting Changes/Merge Conflicts
•Single Unit of Deployment
•Single Point of Failure
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16. user mental model
tends to be UI driven
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17. there is no Spoon Orders Manager
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18. chop
up
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19. Autonomy
Collaborative Domains
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20. sagas autonomy in
collaborative domains
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21. multiple workflows,
each providing
compensating
actions for every
step of the
workflow where it
can fail
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22. multiple workflows,
each providing
compensating
actions for every
step of the
workflow where it
can fail
mauroservienti

23. reserve with the theater
charge my credit card
deal with insurance
ship tickets
deal with their stuff
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24. reservation
finance
insurance
shipping
stuff
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25. Shipping
Finance
Tickets Ordering Saga
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ReservationOrder Checked-out
Payment Authorized
Order Created
Payment Succeeded
Available Tickets
Select tickets
Shopping Cart
Proceed to checkout
workflow
workflow
workflow

26. Shipping
Finance
Tickets Ordering Saga
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ReservationOrder Checked-out
Payment Authorized
Order Created
Payment Succeeded
Available Tickets
Select tickets
Shopping Cart
Proceed to checkout
Policy
Policy
Policy

27. Shipping
Finance
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Reservation
Available Tickets
Select tickets
Shopping Cart
Proceed to checkout
Policy
Policy
Policy
Order Checked-out
Payment Authorized
Order Created
Payment Succeeded
Pivotal Events

28. mauroservienti
Let’s open the black box

29. Shipping
ReservationPayment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Courier
Gateway
Tickets Ordering Saga
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Available Tickets
Select tickets
Reservation
Shopping Cart
Proceed to checkout
Reservation
Order Checked-out
Payment Authorized
Order CreatedFinance
Payment
Gateway
Charge Card
Payment Succeeded Delivery Pick-up
Order Shipped

30. multiple workflows,
each providing
compensating
actions for every
step of the
workflow where it
can fail
mauroservienti

31. Shipping
ReservationPayment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Courier
Gateway
Tickets Ordering Saga
mauroservienti
Available Tickets
Select tickets
Reservation
Shopping Cart
Proceed to checkout
Reservation
Order Checked-out
Payment Authorized
Order CreatedFinance
Payment
Gateway
Charge Card
Payment Succeeded Delivery Pick-up
Order Shipped

32. Payment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Payment Policy
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Order Checked-out
Payment Authorized
Finance
Payment
Gateway
Charge Card
Payment Succeeded

33. Payment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Payment Policy
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Order Checked-out
Payment Authorized
48hrs to release money

34. Payment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Payment Policy
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Order Checked-out
Payment Authorized
Finance
Payment
Gateway
Charge Card
Payment Succeeded
48hrs to release money
Payment
Gateway
Release Money
Reserved?N
Y
Do nothing… Reservation
Order Created
48hrs later…

35. New requirement
• A ticket must be purchased within 10 minutes
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36. Shipping
ReservationPayment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Courier
Gateway
Tickets Ordering Saga
mauroservienti
Available Tickets
Select tickets
Reservation
Shopping Cart
Proceed to checkout
Reservation
Order Checked-out
Payment Authorized
Order CreatedFinance
Payment
Gateway
Charge Card
Payment Succeeded Delivery Pick-up
Order Shipped

37. Reservation
Reservation Policy
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Available Tickets
Select tickets
Reservation Tickets Reserved
10’ to purchase
Reservation
Release Tickets
N
Y
Do nothing…
Checked-out?Reservation Expired

38. Shipping
ReservationPayment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Courier
Gateway
Tickets Ordering Saga
mauroservienti
Available Tickets
Select tickets
Reservation Tickets Added to Cart Reservation
Shopping Cart
Proceed to checkout
Reservation
Order Checked-out
Payment Authorized
Order CreatedFinance
Payment
Gateway
Charge Card
Payment Succeeded Delivery Pick-up
Order Shipped
10’ to purchase
48hrs to release money

39. New requirement
• 12-hours delivery SLA with our customers
• if the default shipping courier doesn't respond
• contact another one to deliver the package
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40. Shipping
ReservationPayment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Courier
Gateway
Shipping Policy
mauroservienti
Available Tickets
Select tickets
Reservation Tickets Added to Cart Reservation
Shopping Cart
Proceed to checkout
Reservation
Order Checked-out
Payment Authorized
Order CreatedFinance
Payment
Gateway
Charge Card
Payment Succeeded Delivery Pick-up
Order Shipped
10’ to purchase
48hrs to release money

41. Shipping
Order Shipped
…
First Courier
Gateway
Pick-up Request
Shipping
Shipping
Second Courier
Gateway
Pick-up Request
Shipping
Shipping
Have we received a response?
Shipment Failed
…
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8hrs timeout
Shipping Policy
Have we received a response?
?
2hrs escalation timeout
N
N?Y
Y

42. Concurrency
1. Pick-up request to 1st courier
2. 8 hours go by
3. No response yet
4. Pick-up request to 2nd courier
5. 2nd courier replies
6. 1st courier replies…Ooops
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43. mauroservienti
It’s a business problem

44. Sagas (a different point of view)
OrderId ShippingId ShippingStatus Etc
12 1337 Delivered …
58 1338 Pending …
Orders table
Reservation Shipping Finance
Id TicketId
12 ABC
58 ACD
Reservations table
OrderId Address
12 Haifa, Israel
58 Rotterdam, Holland
Shipping table
OrderId Status
12 Paid
58 Overdue
Invoices table
VS
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45. Sagas (a different point of view)
Reservation Shipping Finance
Id TicketId
12 ABC
58 ACD
Reservations table
OrderId Address
12 Haifa, Israel
58 Rotterdam, Holland
Shipping table
OrderId Status
12 Paid
58 Overdue
Invoices table
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Each service can evolve independently

46. Sagas
•Business Process is distributed
•No overarching Process Manager
•Respect Single Responsibility Principle
•Independent scale out
•Simpler/not conflicting evolution
•Independent Units of Deployment
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47. Every year is getting shorter never seem to find the time…
Sagas Demo
bit.ly/xe-state-machine
Udi Dahan about Sagas
go.particular.net/xe-state-machine
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48. Demos: bit.ly/xe-state-machine
Videos: go.particular.net/xe-state-machine
Pitfalls
• Monitor the (distributed) state
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49. Demos: bit.ly/xe-state-machine
Videos: go.particular.net/xe-state-machine
Pitfalls
• Monitor the (distributed) state
• There is no such thing as orchestration
• Sagas spanning multiple services
mauroservienti

50. Demos: bit.ly/xe-state-machine
Videos: go.particular.net/xe-state-machine
Takeaways
• Boundaries are key to success
• Finding boundaries is the hardest part
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51. Demos: bit.ly/xe-state-machine
Videos: go.particular.net/xe-state-machine
Takeaways
• Boundaries are key to success
• Behaviors define how to designs processes
• Follow the coupling, not the data
• Identify processes and chop them up by “service”
mauroservienti

52. Demos: bit.ly/xe-state-machine
Videos: go.particular.net/xe-state-machine
Takeaways
• Boundaries are key to success
• Behaviors define how to designs processes
• Use Delayed Messaging to model time
• Simplifies making decisions in an async world
mauroservienti

53. @mauroservienti | #EDDD
Mauro Servienti
Solution Architect @ Particular Software
the makers of NServiceBus
mauro.servienti@particular.net
@mauroservienti
//github.com/mauroservienti
//milestone.topics.it
mauroservienti

54. @mauroservienti | #EDDD
Demos: bit.ly/xe-state-machine
Videos: go.particular.net/xe-state-machine
mauroservienti