Azure Functions

Azure Functions is a serverless compute service that runs your code on-demand, billing only for execution time — no servers to manage, no idle costs.

Simple Explanation

A light-switch: you wire it up, and it turns on only when something flips it. Functions execute in response to events, then stop — you pay only for the milliseconds they run.

When to Use Functions

• Event-driven tasks: process a blob upload, respond to a queue message, fire on a timer.
• Lightweight HTTP APIs where per-request pricing is cheaper than running a server 24/7.
• Automation scripts (nightly cleanup, report generation).
• Glue code that connects services without building a full microservice.

Triggers

Hosting Plans

Visual Representation

Commands

# Install Functions Core Tools (local dev)
npm install -g azure-functions-core-tools@4

# Initialize a new function project
func init my-func-app --worker-runtime node

# Create a new HTTP-triggered function
cd my-func-app
func new --name HelloWorld --template "HTTP trigger"

# Run locally
func start

# Create storage account (Functions require one)
az storage account create \
  --name stfuncstorage2024 \
  --resource-group rg-functions \
  --sku Standard_LRS

# Create a Function App (Consumption plan)
az functionapp create \
  --resource-group rg-functions \
  --consumption-plan-location eastus \
  --runtime node \
  --runtime-version 18 \
  --functions-version 4 \
  --name fn-app-myproject \
  --storage-account stfuncstorage2024

# Deploy code
func azure functionapp publish fn-app-myproject

# View logs
az webapp log tail --name fn-app-myproject --resource-group rg-functions

Hands-on

1. Install Core Tools and create a local HTTP function in Node.js or Python.
2. Run locally with func start and test via curl http://localhost:7071/api/HelloWorld.
3. Create a Function App on Consumption plan and deploy.
4. Add a Timer trigger function with CRON expression 0 */5 * * * * (every 5 min).
5. View execution logs in the Portal under Monitor.

Debugging Scenario

Issue: HTTP function returns errors only under load.

• Consumption plan may be cold-starting under sudden traffic spikes.
• Check Application Insights for dependency timeouts (database connection pool exhausted).
• Functions on Consumption share infrastructure — move to Premium for consistent performance.
• Enable Application Insights and track function execution times per invocation.

Interview Questions

Summary

Azure Functions is ideal for event-driven, short-lived workloads. Consumption plan is cheapest for infrequent or variable workloads; Premium removes cold starts for production APIs. Always pair Functions with Application Insights for observability.