Stateless all the thing, they say. In the last few years we’ve been brainwashed: design stateless systems, otherwise they cannot scale, they cannot be highly available, and they are hard to maintain and evolve. In a nutshell stateful is bad. However complex software systems need to do collaborative processing, that is stateful by definition. Stateless myth busted! Collaborative domains deal with long running business transactions and need to interact with distributed resources. The traditional distributed transactions approach, even if tempting, is a time bomb. This is when Sagas come into play. Sagas allow to model complex collaborative domains without the need for distributed transactions and/or orchestration across multiple resources. Join Mauro on a journey that aims to disclose what sagas are, how they can be used to model a complex collaborative domain, and what role they play when it comes to designing systems with failure and eventual consistency in mind. (It’s all right, I know where you’ve been)

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

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

3. mauroservienti

4. buy ticket(s)
stage dive… :-)
mauroservienti

5. All what they want to do is…
mauroservienti

6. mauroservienti

7. display available tickets
reserve ticket(s)
charge my credit card
ship ticket(s)
mauroservienti

8. sometimes order doesn’t matter
sometimes it does!
mauroservienti

9. Naïve way
var seats = await DisplayAvailableSeats();
var selectedSeats = seats.Take(2);
var reservation = await ReserveSeats(selectedSeats);
var authorization = await AuthorizeCard(reservation);
if (authorization.Succeeded)
{
await ChargeCard(authorization);
await ShipTickets(reservation);
}
mauroservienti

10. Naïve way
var seats = await DisplayAvailableSeats();
var selectedSeats = seats.Take(2);
var reservation = await ReserveSeats(selectedSeats);
var authorization = await AuthorizeCard(reservation);
if (authorization.Succeeded)
{
await ChargeCard(authorization);
await ShipTickets(reservation);
}
Remote requests
mauroservienti
Remote requests

11. Tickets Selection
Credit Card
Gateway/ACL
Orders Manager
Order Checked-out
AuthorizeCard
request/response
Reservation
ConfirmTickets
request/response
Credit Card
Gateway/ACL
ChargeCard
request/response
Shipping
Gateway/ACL
Shiptickets
request/response
mauroservienti
Reservation
SelectTickets
request/response
Process Managers

12. Tickets Selection
Credit Card
Gateway/ACL
Orders Manager
Checkout request
AuthorizeCard
request/response
Reservation
ConfirmTickets
request/response
Credit Card
Gateway/ACL
ChargeCard
request/response
Shipping
Gateway/ACL
Shiptickets
request/response
Some sort of orchestration is still required
mauroservienti
Reservation
SelectTickets
request/response
Process Managers

13. Orchestration is not the only
issue we should get rid of…

14. Process Managers (a different point of view)
New requirement: collect tickets at the venue
OrderId ShippingId ShippingStatus Etc
12 1337 Delivered …
58 1338 Pending …
Orders table
mauroservienti

15. mauroservienti
like a punch card
Process Managers
own the process

16. Ticket(s)
Insurance
mauroservienti

17. Process Managers, a retrospective.
•Violate Single Responsibility Principle
•Single Unit of Deployment
•Conflicting Changes/Merge Conflicts
•Contention/Performance Bottleneck
mauroservienti

18. mauroservienti
there is no Spoon
Process Manager

19. chop
up
mauroservienti

20. Autonomy
Collaborative Domains
mauroservienti

21. sagas autonomy in
collaborative domains
mauroservienti

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

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

24. reserve ticket(s)
charge my credit card
ship tickets
mauroservienti

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

27. Shipping
Finance
mauroservienti
Reservation
Available Tickets
Select tickets
Shopping Cart
Proceed to checkout
Policy
Policy
Policy
Reservation
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
mauroservienti
Available Tickets
Select tickets
Reservation
Shopping Cart
Proceed to checkout
Reservation
Reservation
Checked-out
Payment Authorized
Order CreatedFinance
Payment
Gateway
Charge Card
Payment Succeeded Delivery Pick-up

30. Sounds more complex than
the naïve approach, doesn’t it?
mauroservienti

31. New requirement
• Collect tickets at the venue
mauroservienti

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

33. Order Created Payment Succeeded
NY
Batch Shipping
at the Venue
Policy
Store for Venue
Delivery
Mark as Complete
Courier
Gateway
Batch Delivery Pick-up
Courier
Gateway
Delivery Pick-up
Deliver Tickets
Mark as Complete
mauroservienti
Shipping Policy
Shipping Policy
Delivery-Mode:
- Collect-at-the-Venue
- Ship-at-Home
?
Is Collect-at-the-Venue?

34. Order Created Payment Succeeded
NY
Store for Venue
Delivery
Mark as Complete
Courier
Gateway
Delivery Pick-up
Deliver Tickets
Mark as Complete
mauroservienti
Shipping Policy
Shipping Policy
Delivery-Mode:
- Collect-at-the-Venue
- Ship-at-Home
?
Is Collect-at-the-Venue?
Batch Shipping
at the Venue
Policy
Courier
Gateway
Batch Delivery Pick-up
Mark as Complete

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

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
Reservation
Checked-out
Payment Authorized
Order CreatedFinance
Payment
Gateway
Charge Card
Payment Succeeded Delivery Pick-up

37. Payment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Payment Policy
mauroservienti
Reservation
Checked-out
Payment Authorized
Finance
Payment
Gateway
Charge Card
Payment Succeeded
Do we need a
Reservation Failed event?

38. Payment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Payment Policy
mauroservienti
Payment Authorized
48hrs to release money
Reservation
Checked-out

39. Reservation
Checked-out
Payment
Gateway
Finance
Finance
Initiate Payment
Authorize Card
Payment Policy
mauroservienti
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…
Mark as Complete

40. What’s a timeout?
void Handle(ReservationCheckedout evt)
{
Send(new AuthorizationRequest(…));
}
void Handle(AuthorizationRequest msg)
{
var authId = await AuthorizeCard(…);
Reply(new AuthorizationResponse(authId));
}
void Handle(AuthorizationResponse msg)
{
Publish(new PaymentAuthorized());
RequestTimeout(TimeSpan.FromHours(48));
}
void Timeout()
{
if(NotReserved){ … }
}
Payment
Gateway
Finance
Authorize Card
Payment Authorized
48hrs to release money
Reservation
Checked-out
Reserved?
Payment
Gateway
FinanceFinanceFinance

41. What’s a timeout?
void Handle(ReservationCheckedout evt)
{
Send(new AuthorizationRequest(…));
}
void Handle(AuthorizationRequest msg)
{
var authId = await AuthorizeCard(…);
Reply(new AuthorizationResponse(authId));
}
void Handle(AuthorizationResponse msg)
{
Publish(new PaymentAuthorized());
RequestTimeout(TimeSpan.FromHours(48));
}
void Timeout()
{
if(NotReserved){ … }
}
Payment
Gateway
Finance
Authorize Card
Payment Authorized
48hrs to release money
Reservation
Checked-out
Reserved?
Payment
Gateway
FinanceFinanceFinance

42. What’s a timeout?
void Handle(ReservationCheckedout evt)
{
Send(new AuthorizationRequest(…));
}
void Handle(AuthorizationRequest msg)
{
var authId = await AuthorizeCard(…);
Reply(new AuthorizationResponse(authId));
}
void Handle(AuthorizationResponse msg)
{
Publish(new PaymentAuthorized());
RequestTimeout(TimeSpan.FromHours(48));
}
void Timeout()
{
if(NotReserved){ … }
}
Payment
Gateway
Finance
Authorize Card
Payment Authorized
48hrs to release money
Reservation
Checked-out
Reserved?
Payment
Gateway
FinanceFinanceFinance

43. Sagas (a different point of view)
OrderId ShippingId ShippingStatus Etc
12 1337 Delivered …
58 1338 Pending …
Orders table
Reservation Shipping Finance
OrderId TicketId
12 ABC
58 ACD
Reservations table
OrderId Address
12 Milan, Italy
58 Paris, France
Shipping table
OrderId Status
12 Paid
58 Overdue
Invoices table
VS
mauroservienti

44. Sagas (a different point of view)
Reservation Shipping Finance
Reservations table
OrderId Address
12 Milan, Italy
58 Paris, France
Shipping table
OrderId Status
12 Paid
58 Overdue
Invoices table
mauroservienti
Each service can evolve independently
OrderId TicketId
12 ABC
58 ACD

45. Sagas
•Business Process is distributed
•Respect Single Responsibility Principle
•Simpler/not conflicting evolution
•Independent Units of Deployment
•Independent scale out
mauroservienti

46. Every year is getting shorter
never seem to find the time…
Sagas Demo
bit.ly/eddd-state-machine
Udi Dahan about Sagas
go.particular.net/eddd-state-machine
mauroservienti

47. Demos: bit.ly/eddd-state-machine
Videos: go.particular.net/eddd-state-machine
Pitfalls
• Monitor the (distributed) state
mauroservienti

48. Demos: bit.ly/eddd-state-machine
Videos: go.particular.net/eddd-state-machine
Takeaways
• Behaviors define how to designs processes
• Follow the coupling, not the data
• Identify processes and chop them up by “service”
mauroservienti

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

50. there is no
such thing as
orchestration
mauroservienti

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

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