Your website shows a page. What happens when a visitor signs in, buys a course, or leaves a comment? The application needs a database to save that information and retrieve it later.
Azure offers several database services, but they solve different problems. Here is a practical guide you can use for your Azure series on DevOps with Patil.
At a glance
| Service | Think of it as | A good fit when… |
|---|---|---|
| Azure SQL Database | A managed Microsoft SQL database | You are building a new application with related tables |
| Azure Cosmos DB | A database built to scale and distribute data | Your app needs flexible records or serves users across regions |
| Azure Database for PostgreSQL | Managed PostgreSQL | Your application uses PostgreSQL |
| Azure Database for MySQL | Managed MySQL | Your application or WordPress setup uses MySQL |
| Azure SQL Managed Instance | A managed SQL Server instance | You are moving an existing SQL Server application to Azure |
1. Azure SQL Database: For structured application data
Imagine building a learning platform with three tables: Students, Courses, and Enrollments. Each enrollment connects a student to a course. Azure SQL Database stores these relationships and lets the application query them using SQL.
Azure manages much of the database infrastructure work, including patching and backups. That makes it a useful starting point for a new application built around the Microsoft SQL Server engine.
Practical flow: A visitor logs in → your backend looks up their student record → it queries enrollments → the website displays their courses.
Interview answer: “I would choose Azure SQL Database for a new application that needs structured, related data and uses the SQL Server engine.”
2. Azure Cosmos DB: For flexible data at scale
Suppose your website grows into a product marketplace. A laptop has RAM and storage fields; a T-shirt has size and colour. With the commonly used Cosmos DB API for NoSQL, you can store these as JSON documents with different fields.
Cosmos DB is also designed for distributed applications and can replicate data across Azure regions. It offers multiple APIs, so the exact data model depends on the API you choose.
Practical flow: A visitor opens a product page → your backend retrieves that product’s document → the page displays its own relevant attributes.
Interview answer: “I would evaluate Cosmos DB when the data structure varies between records or the application needs to scale across regions.”
3. Azure Database for PostgreSQL: For PostgreSQL applications
PostgreSQL is a popular relational database engine. Azure Database for PostgreSQL Flexible Server lets you run a PostgreSQL database through a managed Azure service.
For example, a custom version of DevOps with Patil could store articles, authors, comments, and course progress in PostgreSQL. When a reader opens an article, the backend retrieves its content and comments from the database.
Interview answer: “If my application is built on PostgreSQL, I would use Azure Database for PostgreSQL Flexible Server to host its database in Azure.”
4. Azure Database for MySQL: For MySQL applications and WordPress
MySQL is another relational database engine. Azure Database for MySQL Flexible Server is Azure’s managed option for applications that use it.
A familiar example is WordPress: its database stores posts, pages, user accounts, and site settings. If you were designing an Azure hosted WordPress setup, Azure Database for MySQL could be the database component. This is an example architecture, not a claim about where your current website is hosted.
Interview answer: “I would choose Azure Database for MySQL when the application already depends on MySQL, such as a WordPress website.”
5. Azure SQL Managed Instance: For existing SQL Server systems
Picture a company with an established application running on its own SQL Server. Moving it to a new cloud database may require changes if it depends on SQL Server instance features.
Azure SQL Managed Instance provides broad compatibility with SQL Server in a managed Azure service. It is therefore a strong option to evaluate for migrations, although the team must check the application’s exact features and dependencies first.
Practical example: A company assesses its existing reporting and transaction databases, checks their SQL Server dependencies, and plans a migration to SQL Managed Instance where those dependencies are supported.
Interview answer: “I would evaluate SQL Managed Instance when migrating an existing SQL Server application that needs instance level compatibility.”
The difference people often miss
Azure SQL Database and SQL Managed Instance both use the SQL Server database engine. The usual decision is whether you are building a new database focused application or migrating an existing SQL Server workload with more instance level dependencies.
PostgreSQL and MySQL are different database engines. Choose the one your application supports; their Azure services do not make them interchangeable.
Cosmos DB is a different design choice. Consider its data model, access patterns, scale, and regional needs before selecting it simply because an application has a lot of data.
Quick selection guide
- New application using SQL Server: Azure SQL Database
- Application already using PostgreSQL: Azure Database for PostgreSQL
- Application already using MySQL or WordPress: Azure Database for MySQL
- Flexible documents or multi-region application: Evaluate Azure Cosmos DB
- Existing SQL Server migration with instance dependencies: Evaluate Azure SQL Managed Instance
Remember: Visitors interact with your website, the backend talks to the database, and the database stores the application’s data. That simple flow helps you explain all five services clearly in an interview.
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