Azure Functions lets you develop serverless applications on Microsoft Azure requires general Azure Storage Account

• Azure Blob
• Queue
• Files and Table storage.

Difference with Azure Logic Apps

For Azure Functions, you develop orchestrations by writing code and using the Durable Functions extension. For Logic Apps, you create orchestrations by using a GUI or editing configuration files (workflow).

Logic Apps

• Logic App code View: extend definitions you use Logic App code View
• Integrate the workflow: Enterprise Integration Pack (EIP)

Hosting Plans

• Consumption plan: Default, only pay for compute resources when your functions are running (1.5 GB or memory / 1 CPU )
• Premium plan: pre-warmed workers
• Dedicated plan: run your function within a AppService - price can be predictive, Best for long-running (Always on should be enabled!)

Deployment

• AppService Environment (ASE)
• Kubernetes (KEDA)

Scaling

scale controller to monitor the rate of events (scale out / in) latency of scaling from zero to one - cold start

Scaling behaviors

• Maximum instances: 200
• New instance rate: new instances allocated HTTP: once per second / Non-Http: once on every 30 seconds

limit scale out by setting functionAppScaleLimit parameter to 0 / null or a valid number

Each function contains:

• Code
• Config (function.json)

Code should be placed in Root and root folder should contains a host.json file contains runtime-specific configuration

triggers and bindings

• Trigger: what cause a function to run. must have exactly 1 trigger!

• Binding: way of connecting another resource (input bindings, output bindings, or both)

  Sample

{
  "bindings": [
    {
      "type": "queueTrigger",
      "direction": "in",
      "name": "order",
      "queueName": "myqueue-items",
      "connection": "MY_STORAGE_ACCT_APP_SETTING"
    },
    {
      "type": "table",
      "direction": "out",
      "name": "$return",
      "tableName": "outTable",
      "connection": "MY_TABLE_STORAGE_ACCT_APP_SETTING"
    }
  ]
}

Types of binding expressions (path parameter in function.json)

• app settings (% sign)
  • The connection property of triggers and bindings is a special case and automatically resolves values as app settings, without percent signs.
• filename {filename}
• Trigger metadata
• JSON payloads
• Dot notation
• Create GUIDs {rand-guid}
• Current time {DateTime}

Return Value using $return in function.json

Connect functions to Azure services

Environment variables default configuration provider

• Application Settings in azure function service
• local setting file

Identity-based connections are not supported with Durable Functions.

Authorization Levels

• Anonymous - No Api Key required.
• function - a function-specific API key is required (default)
• Admin - the master key is required

Durable Functions

a.k.a stateful functions

Application patterns

• Function chaining:

  a sequence of functions executes in a specific orde

  the output of one function is applied to the input of another function

• Fan-out/fan-in:

  execute multiple functions in parallel and then wait for all functions to finish

• Async HTTP APIs:

  HTTP endpoint trigger the long-running action. Then, redirect the client to a status endpoint that the client polls to learn when the operation is finished

  Function must include DurableClient input binding

• Monitor:

  recurring process in a workflow. An example is polling until specific conditions are met

• Human interaction:

  Involving humans in an automated process

  timeouts and compensation logic

Durable Functions types and features

• Orchestrator functions describe how actions are executed and the order in which actions are executed

  • different types of actions, including activity functions, sub-orchestrations, waiting for external events, HTTP, and timers.

• Activity Function: basic unit of work in a durable function. DurableActivityContext as a parameter Activity functions can only have a single value passed to them (Array / Tuple supported!). activity functions only guarantee at least once execution. You can trigger an activity function only from an orchestrator function.

• Entity functions: reading and updating state . Entities are accessed via a unique identifier Operations on entities require that you specify the Entity ID of the target entity, and the Operation name,

• Client functions: The primary way to deliver these messages is by using an orchestrator client binding, or an entity client binding. Any non-orchestrator function can be a client function. What makes a function a client function is its use of the durable client output binding Orchestrator and entity functions cannot be triggered directly using the buttons in Azure Portal

Task hubs

logical container for durable storage resources

Task Hub in Azure Storage resources:

• 1 or more control queue
• 1 work-item queue
• 1 history table
• 1 instance table
• 1 storage container (1 or more lease BLOB)

Durable orchestrations

• define function workflows using procedural code
• call other durable functions synchronously and asynchronously
• Execution progress is automatically checkpointed

Features and patterns

• Sub-orchestrations
• Durable timers
• External events
• Error handling
• Critical sections (LockAsync)
• Calling HTTP endpoints
• Passing multiple parameters (Array / Tuple)

Durable Timers

implement delays or to set up timeouts with context.CreateTimer

Send and wait for events

wait and listen for external events.

handling human interaction or other external triggers

context.WaitForExternalEvent

RaiseEventAsync method takes eventName and eventData as parameters. The event data must be JSON-serializable.