This document provides an overview of Durable Functions in Azure, which allow for long-running workflows and orchestrations in serverless applications. It discusses Azure Functions, sample use cases, the components of Durable Functions including activity functions, orchestrator functions, and client functions. It also demonstrates how Durable Functions work, error handling, constraints on orchestrator functions, and includes a demo of function chaining and fan out/fan in patterns.

1. Durable Functions

2. Amresh Krishnamurthy
◈ Technical Architect, JCPenney
◈ BDotNet Member
◈ @amreshkris

3. Agenda
◈ Serverless in Azure
◈ Azure Functions
◈ Sample Problem
◈ Why we need Durable Functions !
◈ What is Durable Functions !
� Activity Functions
� Orchestrator
� How does it work?
� Workflows
� Error Handling and Resiliency
� Demo

4. Azure Serverless Compute
◈ Serverless computing enables developers to build applications faster by eliminating the
need for them to manage infrastructure. With serverless applications, the cloud service
provider automatically provisions, scales and manages the infrastructure required to run the
code.
Event
Grid
Logic
Apps
Azure Functions

5. Azure Functions - FaaS
Short Lived
Each function is short
lived for its executions
and resources freed-up
after one execution
Stateless
Functions don’t
maintain state
Event-driven |
Dynamic Scaling
Functions are triggered
through events such as
Http trigger, Timer,
Event grid etc.
Pay as per you use
Pay only for the time
the function actively
runs.

6. Sample Business Usecase & Solution

7. Function Chaining
Fan out- Fan
In
Async HTTP API Monitor
Aggregato
r
Approval

8. Hello, Durable Functions
Orchestration of Azure Functions
Durable Functions
are extensions of
Azure Functions.
Azure Function –
Stateless Vs Durable
Function – Can retain
state
Long running
orchestrations as a
single unit.
Coordinate and
Aggregate across
multiple
functions/workflows
Code driven. No
JSON schema files or
no designer involved
Built on Durable Task
Framework and Azure
Function.
Uses Azure storage
for maintaining state.

9. Components
Activity Function
◈ Activity Function – Performs Activity/Unit of work. Tasks being orchestrated
Book Hotel Book Flight
Compute
Total

10. Components
Orchestrator Function
◈ Orchestrator Function – Described how actions are executed and the order in
which they are run.
Orchestrate :
Book Vacation

11. Components
Client Function
◈ Client Function – Entry point for creating an instance of Durable function.
Trigger/Event Based
Trigger : Book
Vacation

12. Durable Function Flow
Starter Function
Orchestrator
Function
Activity Function

13. Demo
◈ Durable Functions – Function Chaining
◈ Fan Out- Fan In
◈ VS Code – Azure Storage Emulator
◈ Source Code - https://github.com/amreshkris/DurableFunctions-FanOutFanIn

14. How Durable functions works !
◈ Pattern Used – Event Sourcing – Maintains each step of the execution in Event/History
Table
◈ ``
Orchestration
Function Called
Orchestration Started
Activity Function F1
Called
Activity Function F1
Scheduled
Execution Instance
Started
Orchestration
Completed
Activity Function F1
Completed
Activity Function F2
Called
Orchestration Started
Activity Function F2
Scheduled
Orchestration
Completed
Orchestration Started
Activity Function F2
Completed
Orchestrator Execution
Completed

15. Error Handling | Resiliency
◈ Demo

16. Orchestrator Function Constraints
◈ Must be deterministic
◈ Avoid Date and Time related API – Use ‘CurrentUtcDateTime’ provided in Durable
functions context
◈ Random Numbers , Async API , Static Variables , Infinite loops etc
theCurrentUtcDateTime

17. References/Links
◈ https://docs.microsoft.com/en-in/azure/azure-functions/durable/
◈ https://github.com/Azure/azure-functions-durable-extension