System Reliability and Resilience

1. SystemReliability and Resilience and stuff

2. Some things need to be cleared up first

3. http://en.wikipedia.org/wiki/Vedette_(cabaret)

4. tuple

5. //Initialize customer and invoiceInitialize(customer, invoice);

6. public void Initialize (Customer customer, Invoice invoice){customer.Name=“asdf”;invoice.Date =DateTime.Now;}

7. Initialize(customer, invoice);//did something happen to customer// and/or invoice?

8. customer.Name =InitNameFrom(customer, invoice);invoice.Date = InitDateFrom(customer, invoice);

9. customer.Name =GetNameFrom(customer, invoice);invoice.Date = GetDateFrom(customer, invoice);

10. var results = Initialize(customer, invoice);customer.Name =results.Item1;invoice.Date = results.Item2;

11. public tuple<string, DateTime>Initialize(customer, invoice){ return new Tuple<string, DateTime> (“asdf”, DateTime.Now);}

12. public static boolTryParse (string s, outDateTime result)orpublic static tuple<bool, DateTime?>TryParse (string s)

13. tuple • Avoid side effects • Avoid out parameters • multiple values without a specific type

14. null object

15. private ILogger _logger;public MyClass(ILogger logger) {_logger = logger;}…if (_logger != null) {_logger.Debug(“it worked on my machine!”);}

16. null checks for everyone!

17. forget one and…

18. public class NullLogger:ILogger{ public void Debug(string text) { //do sweet nothing}}

19. private ILogger _logger = newNullLogger();public MyClass(ILogger logger) {_logger = logger;}…_logger.Debug(“it worked on my machine!”);

20. null object • Can eliminate null checks • Simple to implement

21. Circuit Breaker

23. Retry

24. Your Application Out of Process Dependency N times

25. Out of Process Dependency N times * Y clients

26. = Denial of Service Attack

27. Limit the # of retries

28. N * Ybecomes5 * Y

29. Y isstill aproblem

31. Circuit Breaker

33. State MachineOn :: Off

34. On  Offwhen not healthy

35. Off  Onmanually

36. Get to softwarebefore we ask you to dance

37. HealthyorUnhealthy Out of Process Dependency

38. State is independent of requestor Out of Process Dependency

39. Has many independent external dependencies Your Application

40. Can throttle itself Your Application

41. Has a wait threshold Your Application

42. Circuit Breaker External Dependency Your Application Threshold = 2 Pause = 10ms Timeout = 30s State = Closed Request Request Failure (i.e. HTTP 500) Failure Count = 1 Pause 10ms Request Failure (i.e. HTTP 500) Failure Count = 2 State = Open OperationFailedException

43. Circuit Breaker External Dependency Your Application Threshold = 2 Pause = 10ms Timeout = 30s State = Open System can try to become healthy for 30s Request 30s has not passed CircuitBreakerOpenException Request 30s has not passed CircuitBreakerOpenException

44. Circuit Breaker External Dependency Your Application Threshold = 2 Pause = 10ms Timeout = 30s State = ½ Open 30s has passed Request Request Failure (i.e. HTTP 500) Failure Count = 2 State = Open OperationFailedException

45. Circuit Breaker External Dependency Your Application Threshold = 2 Pause = 10ms Timeout = 30s State = ½ Open 30s has passed Request Request Response Failure Count = 0 State = Closed Response

46. ClosedOpen½ Open

47. ½ Open is like a manual reset

48. PauseTimeout

49. Pausebetween callsin the loop

50. Timeoutbefore youcan call again