MSDEVBUILD / azure

PaaS – Platform as a Service

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

You manageMicrosoft manages
In PaaS, Microsoft also runs the operating system and runtime. You just bring your app and data.

😟 THE PROBLEM

Two developers spend a day every week patching servers instead of coding.

😊 THE SOLUTION

Use PaaS: Microsoft runs the platform, you just deploy your app.

  • Monthly OS patching eats time✓ Microsoft patches the platform
  • Adding servers before busy weeks✓ Built-in autoscale does it for you
  • Worrying about database backups✓ Managed databases back up automatically
🛠️ 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 1: Cloud Concepts ⏱ 9 min read Updated 11 Nov 2026

Quick answer

Platform as a Service (PaaS) is the cloud service type where the provider manages the infrastructure and the platform (operating system, runtime, middleware, patching, often scaling and backups), and you bring your application and data. Developers focus on code, not servers. Azure App Service and Azure SQL Database are typical examples.

Exam objective: 1.3.2 Describe platform as a service (PaaS). (Skills measured as of July 20, 2026)

Start with a question

Do you want to bake a cake, or do you want to build an oven, wire the kitchen and then bake a cake?

Most developers just want to bake the cake: write code and ship features. Yet with plain servers they also have to install operating systems, patch them every month, configure web servers and plan how to scale.

Platform as a Service hands you a ready kitchen. You bring the recipe (your code) and the ingredients (your data).

Explain it like I’m 10

The technical explanation

With Platform as a Service, the provider manages everything IaaS covers (datacenter, hardware, network, virtualisation) plus the operating system, runtime and middleware. It usually adds operational features such as automatic patching, scaling, high availability and backups. You deploy your application and manage your data, identities and access configuration.

  1. 1 Datacenter, hardware, network

    Microsoft

  2. 2 Virtualisation and OS

    Microsoft

  3. 3 Runtime, middleware, patching

    Microsoft

  4. 4 Application

    You (Microsoft runs the platform)

  5. 5 Data, identities, access

    You

The PaaS stack: Microsoft manages more, you focus on the app

PaaS on Azure

Azure serviceWhat it gives developers
Azure App ServiceHost web apps, REST APIs and mobile back ends in .NET, Java, Node.js, Python or PHP, with autoscale and deployment slots
Azure SQL DatabaseFully managed SQL Server database engine with automated backups, patching and high availability
Azure Cosmos DBGlobally distributed NoSQL database with low-latency reads and writes
Azure FunctionsRun small pieces of code in response to events (also serverless)
Azure Container AppsRun containers without managing Kubernetes clusters
Architect level Designing for PaaS: what changes in your architecture
  • Stateless instances: the platform adds and removes instances, so keep session state in Azure Managed Redis or a database, and files in Blob Storage, not on local disk.
  • Configuration and secrets: use app settings plus Azure Key Vault references, and authenticate with managed identities instead of connection-string passwords.
  • Networking: PaaS endpoints are public by default. Lock them down with access restrictions, VNet integration for outbound traffic and private endpoints for inbound.
  • Release safety: App Service deployment slots let you warm up and swap releases with no downtime and instant rollback.
  • Limits: every PaaS service has quotas (connections, request size, timeouts). Read them early. They shape the design.

Real-world business scenario

Online education

An online learning platform

The problem
Three developers were spending a day a week patching VMs and manually adding servers before exam weeks.
What they used
Moved the web front end and API to Azure App Service with autoscale rules, the database to Azure SQL Database, and course videos to Blob Storage.
Why that choice
PaaS removed OS patching and manual scaling, and gave built-in backups and high availability without a dedicated operations hire.
The result
The patching day disappeared from the calendar, exam-week scaling became automatic, and releases became daily with deployment slots.

When to use it and when not to

✓ Use it when…

  • Web apps, APIs and mobile back ends built on mainstream runtimes.
  • New development where you want speed and minimal operations.
  • Managed databases where you want automatic backups, patching and HA.
  • Small teams without dedicated infrastructure staff.

✕ Think twice when…

  • The software needs OS-level customisation, special drivers or unsupported runtimes.
  • Strict requirements to control patch timing at OS level.
  • Ported legacy apps that rely heavily on local machine state. Refactor first, or use IaaS.

↔ Alternatives to consider

  • **IaaS** VMs when you need full control.
  • **Containers** on Container Apps or AKS for portable packaging with more control than App Service.
  • **SaaS** if an existing product already does what you were about to build.
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 PaaS? Give an Azure example.

Model answer

PaaS is a cloud service where the provider manages the servers, operating system and runtime, and I just deploy my application and manage my data. Azure App Service for hosting web apps and APIs, and Azure SQL Database for managed databases, are examples.

Interviewer follows up

What do you still have to manage?

You

My application code and its configuration, my data, who has access (identities and permissions), and some settings like network access rules. Microsoft handles OS patching, the runtime and the underlying infrastructure.

Intermediate What are the benefits and limitations of PaaS for a development team?

Model answer

Benefits are faster development, no OS patching, built-in scaling, high availability, backups and deployment slots, and often lower total cost because less operations work is needed. Limitations are less control over the environment (you cannot install anything on the OS), supported runtimes and versions only, platform-specific features that can increase lock-in, and service limits you must design around.

Experienced developer A team wants to move a .NET API from VMs to Azure App Service. What would you check first?

Model answer

Dependencies on the local machine (file system writes, the Windows registry, GAC components, installed COM libraries, local scheduled tasks), session state stored in memory (move it to Redis), configuration and secrets (move to app settings and Key Vault with managed identity), outbound IP and firewall needs, private connectivity to databases (VNet integration, private endpoints), and the right plan tier for scale-out and slots. Then I would set up deployment slots for zero-downtime releases.

Scenario Two developers are building a new e-commerce API and have no operations staff. IaaS or PaaS?

Model answer

PaaS. App Service for the API and Azure SQL Database for data. They avoid OS patching, get autoscaling and backups built in, and can spend their time on features.

Test yourself with exercises

4 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 4

Which cloud service type lets developers deploy applications without managing the underlying operating system?

Question 2

Question 2 of 4 · Select 2

Which TWO Azure services are examples of PaaS?

Question 3

Question 3 of 4

In a PaaS deployment, which of the following remains the customer's responsibility?

Question 4

Question 4 of 4

A two-person team is building a new web API. They want automatic scaling and do not want to patch servers.

Which service type best fits?

Quick revision

Key points

  • PaaS = provider manages infrastructure and OS, runtime, middleware; you manage apps and data.
  • Built-in features usually include scaling, high availability, patching and backups.
  • Azure examples are App Service, Azure SQL Database, Azure Cosmos DB, Azure Functions and Azure Container Apps.
  • Ideal for developers who want to focus on code.
  • Trade-off is less control over the environment than IaaS.

Important terminology

PaaS
Platform as a Service. The provider runs the OS, runtime and middleware; you deploy apps and manage data and access.
Runtime
The environment your code needs to run, such as .NET, Node.js, Java or Python.
Middleware
Software between the OS and your app, such as web servers or database engines.
Managed service
A service where the provider handles operations like patching, backups and high availability for you.

Common mistakes

  • Thinking PaaS means zero responsibility. You still own your code, data, identities and access settings.
  • Assuming any software can run on PaaS. You cannot install arbitrary OS-level components.

Exam tips

  • "Developers focus on code, not managing servers or OS" = PaaS.
  • "Managed database with automatic patching and backups" = PaaS (for example Azure SQL Database).

Five quick revision questions

  1. 1.What does PaaS stand for?Show

    Platform as a Service.

  2. 2.Who patches the operating system in PaaS?Show

    The cloud provider.

  3. 3.Name two Azure PaaS services.Show

    Azure App Service and Azure SQL Database (also Cosmos DB, Functions, Container Apps).

  4. 4.What is the main trade-off of PaaS compared with IaaS?Show

    Less control over the underlying OS and environment.

  5. 5.Who is responsible for the application code in PaaS?Show

    The customer.

Official references

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