The document discusses using Durable Functions to manage state in Azure Functions. Durable Functions allow for adding state management, checkpoints, and restarts to address limitations of stateless Azure Functions. It describes Durable Function components like orchestrators and activities that can be used to build workflows. Examples are given of how Durable Functions can be used to implement patterns like function chaining, fan-out/fan-in, human interaction, and aggregation that are difficult to do with stateless functions. Durable Entities are also introduced as a way to define operations for reading and updating small pieces of state.

1. Azure Technical Trainer
Stateful pattern con Azure
Functions
Massimo Bonanni
Azure Technical Trainer @ Microsoft
massimo.bonanni@microsoft.com
@massimobonanni

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Azure
What are Azure Functions?
Author functions in
C#, F#, Node.JS, Java,
and more
Code
Events
React to timers, HTTP, or
events from your favorite
Azure services, with more
on the way
Outputs
Send results to an
ever-growing
collection of services

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Functions must be stateless
Functions cannot call other functions
Functions should do only one thing
Principles and best practices…

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Workflow manages state
Workflow is interactions between
components
Workflows must do more than one
thing
… and workflows!?!?!

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Azure Functions
Extension
Based on Azure
Functions
Adds new Triggers and
Bindings
Manages state,
checkpoints, and
restarts
Durable Task
Framework
Long running persistent
workflows in C#
Used within various
teams at Microsoft to
reliably orchestrate long
running operations
Languages
C#
JavaScript
F#
Python
Powershell
What are Durable Functions?

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Durable Function components
Client
Is the triggered functions
that will create new
instances of an
orchestration.
It is the entry point for
creating an instance of a
durable orchestration
Orchestrator
Is the heart of a durable
function.
Orchestrator functions
describe the way and
order actions are
executed.
Activity
Is the basic unit of work
in a durable
orchestration.
An activity function must
be triggered by
an activity trigger.

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Function chaining
Relations between functions and queues aren’t clearly identifying
Queues are an implementation detail
Operation context management is difficult
Error handling is difficult

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Function chaining in Durable Functions
Orchestrator Function
Activity Functions

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Function chaining in Durable Functions

10. Azure Technical Trainer
Event History

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Fan-Out/Fan-In
Fan-Out is simple, but Fan-In is more complicated
The platform must track progress of all work
All the same issues of Function Chain

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Fan-Out/Fan-In in Durable Functions

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Fan-Out/Fan-In in Durable Functions

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Human interaction
Handling race conditions between timeouts and
approval
Need mechanism for implementing and cancelling
timeout events
Same issues as the other pattern

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Human Interaction in Durable Functions

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Human Interaction in Durable Functions

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Aggregator
Storing the state
Correlation of event for a particular state
Syncronization of access to the state

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Entity Functions define
operations for reading and
updating small piece of
state
Entity Functions are
functions with special
trigger
Entity Functions are
accessed using:
• Entity Name
• Entity key
Entity Functions expose
operations that can be
accessed using:
• Entity Key
• Operation Name
• Operation Input
• Scheduled time
Durable Entities aka Entity Functions

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Anatomy of an Entity
Properties (state)
Operations
Entry Function

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Designed for reliability, not for latency
Workflow by code
Durable Entities are similar to Virtual Actor
Solve the concurrency issues, but is it the
right choice?
Takeaway

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Thanks for your
attention!!!!!
Massimo Bonanni
Azure Technical Trainer
massimo.bonanni@microsoft.com
@massimobonanni
Connectwith me on LinkedIn
linkedin.com/in/massimobonanni/
http://bit.ly/MasteringServerless

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References
Photo by Jaredd Craig on Unsplash
https://docs.microsoft.com/en-US/azure/azure-functions/
https://docs.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-
overview?tabs=csharp
https://docs.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-dotnet-
entities
https://docs.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-
entities?tabs=csharp
https://docs.microsoft.com/en-us/azure/azure-functions/durable/quickstart-python-vscode
https://github.com/Azure/durabletask
https://github.com/massimobonanni/StatefulPatternFunctions