MSDEVBUILD / azure

Azure App Service

Your data
Application
Runtime
Operating system
Virtualisation
Servers and storage
Networking
Datacenter

You manageMicrosoft manages
App Service is PaaS: Microsoft runs the servers and operating system, you bring the website.

😟 THE PROBLEM

Developers spend days patching and scaling the VMs that host a simple website.

😊 THE SOLUTION

Host it on Azure App Service and let Microsoft run the platform.

  • OS patching every month✓ Microsoft patches the platform
  • Manual scaling before busy days✓ Built-in autoscale
  • Risky releases✓ Deployment slots: swap with zero downtime
🛠️ Solved with: Azure App Service
Try it yourself in the Azure simulator No Azure account needed. Cloud Shell: deploy a web app ⌨️ Try it ❯
Module 2: Architecture & Services ⏱ 7 min read Updated 11 Nov 2026

Quick answer

Azure App Service is a fully managed PaaS for hosting web apps, REST APIs and mobile back ends. You deploy your code (.NET, Java, Node.js, Python, PHP) or a container, and Microsoft manages the servers, operating system, patching and load balancing. Built-in features include autoscale, deployment slots, custom domains and HTTPS.

Exam objective: 2.2.4 Describe application hosting options, including web apps, containers, and virtual machines. (Skills measured as of July 20, 2026)

Start with a question

You have built a website. Where does it live so the world can visit it?

You could rent a VM and set up a web server yourself, or you could hand your code to App Service and let Azure run it.

Explain it like I’m 10

The technical explanation

Azure App Service hosts web apps, API apps and mobile back ends on Windows or Linux. You deploy code or containers through Git, GitHub Actions, Azure DevOps, ZIP or FTP.

FeatureWhy it helps
AutoscaleMore instances when traffic rises
Deployment slotsZero-downtime releases with swap and rollback
Custom domains and HTTPSProfessional, secure sites
Built-in authenticationSign-in with Microsoft Entra ID and others
VNet integration and private endpointsPrivate connectivity to databases and services

Real-world business scenario

Online education

An online education start-up

The problem
Developers spent too much time managing VMs for their course website and API.
What they used
Moved the website and API to App Service (Standard tier) with autoscale and deployment slots.
Why that choice
PaaS removes OS management and makes releases safe.
The result
Releases became daily with zero downtime, and server maintenance work disappeared.

When to use it and when not to

✓ Use it when…

  • Websites, REST APIs and mobile back ends on common runtimes.
  • Teams that want to focus on code.

✕ Think twice when…

  • Apps needing OS-level customisation (use VMs).
  • Short event-driven jobs (use Functions).
Ready for more?The full lesson adds the technical explanation, when to use it, interview questions and revision notes.

Interview preparation

Say your answer out loud first, then open the model answer. Interviewers care more about your reasoning than the exact words.

Beginner What is Azure App Service?

Model answer

A PaaS service for hosting websites and APIs. I upload my code and Azure runs it on servers it manages, including OS updates, scaling and HTTPS.

Intermediate What is an App Service plan, and how does pricing work?

Model answer

The plan defines the region, the instance size and the number of instances. I pay for the plan, not per app, so several apps can share one plan. Tiers range from Free and Basic to Standard and Premium, which add features such as autoscale, deployment slots and VNet integration.

Experienced developer How do you release a new version to App Service with zero downtime?

Model answer

Deploy to a staging deployment slot, warm it up and test it, then swap it with production. The swap is near-instant, and if something goes wrong I swap back. Slot-specific settings keep things like connection strings separate.

Test yourself with exercises

3 original practice questions in the AZ-900 style. Pick your answers, then check them. You will see why each option is right or wrong. Score 75% or more and this topic is marked complete.

Question 1

Question 1 of 3

Which Azure service hosts web apps and REST APIs without you managing the underlying servers?

Question 2

Question 2 of 3

What do you pay for in Azure App Service?

Question 3

Question 3 of 3

Which App Service feature enables zero-downtime releases?

Quick revision

Key points

  • App Service = PaaS for web apps, APIs and mobile back ends.
  • Microsoft manages servers, OS, patching and load balancing.
  • You pay for the App Service plan; several apps can share one.
  • Features include autoscale, deployment slots, custom domains and HTTPS.

Important terminology

App Service plan
The set of compute resources (size and number of instances) your apps run on, and what you pay for.
Deployment slot
A live staging copy of your app you can swap into production with no downtime.
Web app
An App Service app that hosts a website or web API.

Common mistakes

  • Thinking you manage the VMs behind App Service.

Exam tips

  • "Host a web app without managing servers" = Azure App Service.

Five quick revision questions

  1. 1.Which cloud service type is App Service?Show

    PaaS.

  2. 2.What do you pay for in App Service?Show

    The App Service plan (instance size and count).

  3. 3.What is a deployment slot?Show

    A staging copy of an app that can be swapped into production with no downtime.

  4. 4.Name three app types App Service can host.Show

    Web apps, REST APIs and mobile back ends.

  5. 5.Who patches the OS behind App Service?Show

    Microsoft.

Official references

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Next up: Azure Functions