The document discusses availability and introduces the Polly library. It defines availability as the probability a system works as required when required. It provides availability level tables and discusses how factors like reliability, maintenance and dependencies impact availability. It then introduces Polly as a .NET library that implements resilience patterns like retry, circuit breaker and fallback to make systems more robust and reliable when facing transient faults. It includes a demo of Polly and takes away that high availability increases user confidence and tools like Polly simplify fault handling.

1. B E N J A M I N FA N

2. AGENDA
• Availability
• Introduction Polly
• Demo
• Takeaway
• Appendix

3. A LONG TIME AGO IN WWW

4. NESTED TRY CATCH

5. AVAILABILITY

6. AVAILABILITY
• Availability is the probability that a system will work as required when required during the
period of a mission.
• The mission could be the 18-hour span of an aircraft flight.The mission period could also be
the 3 to 15-month span of a military deployment.Availability includes non-operational periods
associated with reliability, maintenance, and logistics.

7. AVAILABILITY (CONT.)
Availability level Allowed unavailability window
per year per quarter per month per week per day per hour
99.5% 1.83 days 10.8 hours 3.6 hours 50.4 minutes 7.20 minutes 18 seconds
99.9% (3 nines) 8.76 hours 2.16 hours 43.2 minutes 10.1 minutes 1.44 minutes 3.6 seconds
99.95% 4.38 hours 1.08 hours 21.6 minutes 5.04 minutes 43.2 seconds 1.8 seconds
99.99% (4 nines) 52.6 minutes 12.96 minutes 4.32 minutes 60.5 seconds 8.64 seconds 0.36 seconds
99.999% (5 nines) 5.26 minutes 1.30 minutes 25.9 seconds 6.05 seconds 0.87 seconds 0.04 seconds

8. AVAILABILITY (CONT.)
client
DB
3rd
Service
Service
A
Service
B
Service
dependency
Murphy's Law

9. AVAILABILITY (CONT.)
• Why availability matter?
– https://aws.amazon.com/en/legal/service-level-agreements/
– https://azure.microsoft.com/en-us/support/legal/sla/summary/
– https://cloud.google.com/compute/sla-20171130

10. INTRODUCTION
POLLY

11. WHAT IS POLLY
• A .NET resilience and transient-fault-handling library.
• transient-fault:
– Something unexpected happened occasionally
• Ex. network peak or unstable let service unavailable.
• Ex. 3rd party API (there is no 100% availability)
• Ex.Access unmanaged resource (ex. Database, File)

12. WHY POLLY
• Using fluent API and thread safe way to implement Retry, Circuit breaker,Time out, Bulkhead
isolation and Fallback policy。
• Can implement multi fault handle in one place.
• Make system more robust.
• Focus on business logic rather than fault-handling.

13. RETRY
• Basic Concept:
– Don’t play sick

14. RETRY (CONT.)
• Before we use Polly
• Retry mechanism =
count + for loop + try
catch

15. FALLBACK
• Basic Concept:
– There is always a plan B
start
Execute
delegate
exception
Fallback
handle
Return result
Execute
fallback
delegate
end
Yes
Yes
No
No

16. FALLBACK (CONT.)
• Before we use Polly
• When you invoke something in catch that
might throw exception again, will you try
catch of that? Hummmm…

17. DEMO

18. DEMO
• Source code:
– https://github.com/RiceBen/DotNetPollyEssential

19. TAKEAWAY

20. TAKEAWAY
• Things will go wrong, always prepare for the worst case
• High Availability make your user (or customer) more confidence
• Sharp tools make good work.
– Using policy wrap to make fault-handling more easy
– Use proper policy

21. APPENDIX

22. APPENDIX – CHAOS ENGINEERING
• Principles:
– https://principlesofchaos.org/?lang=ENcontent
Chaos engineering can be used to achieve resilience against:
• Infrastructure failures
• Network failures
• Application failures

23. APPENDIX - LIBRARY
.NET Solution
• Simmy
– https://github.com/Polly-Contrib/Simmy
• Polly
– https://github.com/App-vNext/Polly
Java Solution
• Cthulhu
– https://github.com/xmatters/cthulhu-chaos-testing
• Resilience4j
– https://github.com/resilience4j/resilience4j

24. APPENDIX - LIBRARY
Javascript Solution
• Pollyjs
– https://github.com/Netflix/pollyjs
Golang
• Goresilience
– https://github.com/slok/goresilience
• Fuzz-monkey
– https://github.com/ChrisCooney/fuzz-monkey

25. READ MORE
• Making the Netflix API More Resilient
– https://netflixtechblog.com/making-the-netflix-api-more-resilient-a8ec62159c2d
• Circuit Breaker
– https://martinfowler.com/bliki/CircuitBreaker.html
• .NET Microservices Architecture
– https://dotnet.microsoft.com/download/e-book/microservices-architecture/pdf