Deep dive into Azure Durable Functions - Ahmed Elharouny Durable Functions is a very powerful extension to Azure Functions, providing stateful orchestration to address many application patterns, allowing developers to focus more on business value rather than infrastructure components. If you have learnt about Azure Functions and ever wondered how different functions can communicate with each other reliably given the nature of a serveless environment, this talk is for you. If you used Azure functions before and felt that most of your effort is spent in avoidable coordination between functions using queues, messages and tables and all the plumbing around that and hoping there is a better way, this talk is for you. Are you already excited about Durable Functions as much as I am and want to avoid some very common pitfalls along your way? This talk is defiantly for you! This talk expects some prior basic understanding of Azure Functions although I promise that even newbies will find thoughts discussed interesting.

1. Deep dive into Azure
Durable Functions
AHMED ELHAROUNY

2. Durability
Durability is being able to last for long time
without becoming damaged.

3. Durability
 Surviving network transient
errors
 Surviving timeouts
 Browser timeout
 Proxy timeout
 Http client timeout
 External services timeout
 Server/Function timeout

4. Durability
 Keeping track of progress with
 Outages
 Crashes
 Shutdowns
 Terminations
 Deployments

5. Durable or not?
EXERCISE

8. Azure durable functions

9. Workflow
Workflow is a series of connected activities that
runs from start to completion to achieve a
business goal.

10. Workflow Orchestration
The planning, coordination and arrangement of
connected activities to achieve desired result.

11. Workflow activity
An activity is the unit of work inside a workflow. It
performs work by consuming input and producing
output.

12. Components of durable functions
 Starter function
 Can be any azure function (any trigger)
 Starts workflow
 Orchestrator function
 Trigger and coordinate activities
 Activity function
 Where work is done

13. Starter function

14. Activity function

15. Orchestrator function

16. Durable functions debugging / event
sourcing
EXERCISE

30. Demo
Human interaction

31. Orchestrator code constraints
Avoid Alternative
DateTime.UtcNow context.CurrentUtcDateTime
Guid.NewGuid() context.NewGuid()
Thread.Sleep(), Task.Delay() context.CreateTimer()
httpClient.SendAsync context.CallActivityAsync()
Code in orchestrator functions has to be deterministic and non-blocking

32. Error handling
• Error handling is an orchestration concern.
• Be aware of what can be retried and what cannot.
• If applicable add compensation activities.

33. Patterns - chaining

34. Patterns - Fan out/fan in
• Schedule activities without awaiting to fan-out
• Use Task.WhenAll to fan-in

35. Patterns – Human Interaction
Orchestrator is waiting for external event
A blob or http trigger raises an event

36. Patterns – Monitoring (polling)
Use context.createTimer to schedule returning back to
orchestrator at a time in future up to 7 days (currently)

37. Internal infrastructure
Status
Replays

38. Conclusion
 Rewinding
 Termination
 WaitForCompletionOrCreateCheckStat
usResponseAsync
 Application Insights integration
 Better insights
 showHistory=true
 showHistoryOutput=true

39. Thank you
Q & A