⚡ Azure Functions

📌 Overview

Azure Functions is a serverless compute service that lets you run event-triggered code without having to explicitly provision or manage infrastructure.

• Philosophy: "Focus on the code, not the plumbing."
• Event-Driven: It sits idle until something happens (e.g., a file is uploaded, a timer hits 9 AM, an HTTP request arrives).

1. Key Concepts

🔫 Triggers

A Trigger is what causes the function to start running.

• Timer Trigger: Run a cleanup job every night at 3 AM.
• HTTP Trigger: Run code when an API endpoint is hit.
• Blob Trigger: Run code when a new image is uploaded to Storage (e.g., to resize it).
• Cosmos DB Trigger: Run code when a new document is added to the database.

  Rule: A function must have exactly one trigger.

🔗 Bindings

Bindings are a declarative way to connect data to your function code. They save you from writing boilerplate connection code.

• Input Binding: "Fetch the specific Blob that triggered this function and give it to me as a variable."
• Output Binding: "Take this result variable and write it to a Queue message."

3. Architecture Flow

      Events (Trigger)           Function App             Action (Output)
      ================           ============             ===============

    +----------------+         +--------------+          +---------------+
    | New Photo      | ------> | Resize Code  | -------> | Save Thumbnail|
    | (Blob Storage) |         | (Serverless) |          | (Blob Storage)|
    +----------------+         +--------------+          +---------------+
            ^                                                   |
            |                                                   v
    +----------------+                                   +---------------+
    | HTTP Request   |                                   | Send Email    |
    | (API Call)     |                                   | (SendGrid)    |
    +----------------+                                   +---------------+

2. Hosting Plans

You pay differently depending on how you host your function.

🥤 Consumption Plan (Serverless)

• Billing: You pay only when the function is running.
• Scaling: Scales automatically to zero when idle.
• Limitations: Cold Start (latency for the first request after being idle), 10-minute max execution time.
• Best For: Unpredictable traffic, cost optimization.

💎 Premium Plan

• Billing: Pre-warmed instances (always ready).
• Benefits: No Cold Start, VNET integration, longer run duration.
• Best For: Production APIs requiring instant response.

🏢 App Service Plan (Dedicated)

• Billing: Monthly fee (you rent the VM).
• Benefits: Run on the same dedicated VMs as your other App Services.
• Best For: Predictable usage, reusing existing infrastructure.

3. 🛠️ Hands-on: Create a Function App

Step 1: Create a Resource Group

az group create --name myResourceGroup --location eastus2

Step 2: Create a Storage Account (Required)

Function Apps require a storage account to manage triggers and logging.

Note: Your subscription has a restricted list of allowed regions.
If eastus2 fails, try: westus2, northeurope, southeastasia.

az storage account create \
  --name priyanshuksharma$RANDOM \
  --resource-group myResourceGroup \
  --location eastasia \
  --sku Standard_LRS

Step 3: Create the Function App

Replace <storage_name> with the name generated above.

az functionapp create \
  --resource-group myResourceGroup \
  --consumption-plan-location eastasia \
  --runtime node \
  --functions-version 4 \
  --name myUniqueFunctionApp$RANDOM \
  --storage-account 

💡 Exam Tips for AZ-900

• Stateless: By default, Azure Functions are stateless (they handle a request and forget).
• Durable Functions: An extension that lets you write stateful functions (e.g., waiting for manual approval in a workflow).
• Max Time: Consumption plan has a timeout (default 5 mins, max 10 mins). For long-running tasks, use a Dedicated plan or Logic Apps.