Chapter 12 — Azure Database Services - Clinux

Overview

Azure offers a comprehensive suite of managed database services — both relational (SQL-based) and non-relational (NoSQL). "Managed" means Azure handles backups, patching, scaling, and high availability automatically.

Azure Database Services:
  ├── Relational (SQL)
  │     ├── Azure SQL Database
  │     ├── Azure SQL Managed Instance
  │     ├── Azure Database for MySQL
  │     ├── Azure Database for PostgreSQL
  │     └── Azure Database for MariaDB
  └── Non-Relational (NoSQL)
        └── Azure Cosmos DB

Relational vs. Non-Relational Databases

Before diving into services, let's clarify the two types:

	Relational (SQL)	Non-Relational (NoSQL)
Structure	Tables with rows and columns	Documents, key-value, graphs, columns
Schema	Fixed schema (defined in advance)	Flexible schema
Query language	SQL	Varies (JSON, APIs, etc.)
Best for	Structured data, transactions	Unstructured, fast, global-scale data
Examples	MySQL, PostgreSQL, SQL Server	Cosmos DB, MongoDB

1. Azure SQL Database

What Is It?

Azure SQL Database is a fully managed relational database service based on the latest stable version of Microsoft SQL Server. It is a PaaS service — Azure handles patching, backups, high availability, and scaling.

Key Features

Feature	Detail
Engine	SQL Server (latest stable)
Deployment	Single database or elastic pool
Scaling	Serverless (auto-pause/resume) or provisioned
High availability	99.99% SLA built-in
Backups	Automatic with up to 35-day retention
Security	Advanced Threat Protection, Always Encrypted, TDE
Geo-replication	Active geo-replication to up to 4 secondary regions

Purchasing Models

Model	Description
DTU (Database Transaction Units)	Bundled CPU + memory + I/O — simpler, less control
vCore	Choose exact CPU, memory, storage — more flexibility

Elastic Pools

An Elastic Pool lets multiple databases share a pool of resources — cost-effective when databases have variable and unpredictable usage.

Elastic Pool (100 DTUs shared)
├── Database A (peak: 40 DTUs)
├── Database B (peak: 30 DTUs)
└── Database C (peak: 40 DTUs)
→ Total peak would be 110 DTUs, but peaks don't overlap → 100 DTUs suffice

When to Use Azure SQL Database

New cloud-native applications using SQL Server
Modernizing existing SQL Server applications
When you want fully managed SQL with minimal DBA overhead

2. Azure SQL Managed Instance

What Is It?

Azure SQL Managed Instance is a fully managed SQL Server instance that offers near-100% compatibility with on-premises SQL Server. It fills the gap between Azure SQL Database (limited features) and running SQL Server in a VM (full management burden).

SQL Database vs. SQL Managed Instance

Feature	Azure SQL Database	SQL Managed Instance
SQL Server compatibility	Most features	Near 100%
Cross-database queries	Not supported	Supported
SQL Agent	Not supported	Supported
Linked servers	Not supported	Supported
VNet integration	Limited	Full native VNet
Migration	Requires app changes	Near lift-and-shift

When to Use SQL Managed Instance

Migrating on-premises SQL Server workloads to Azure with minimal changes
Applications using SQL Server-specific features (SQL Agent, CLR, linked servers)
When full VNet isolation is required

3. Azure Database for MySQL

What Is It?

Azure Database for MySQL is a fully managed MySQL database service in the cloud. Azure manages patching, backups, high availability, and scaling.

Key Features

Feature	Detail
Engine	MySQL Community Edition (5.7 and 8.0)
High availability	Zone-redundant HA with automatic failover
Backups	Automated, up to 35-day retention
Scaling	Burstable, General Purpose, Memory Optimized
Security	SSL enforcement, firewall, VNet integration
Compatibility	Full MySQL compatibility — drop-in replacement

Deployment Options

Option	Description
Flexible Server	Latest, recommended — full control over maintenance windows
Single Server	Legacy option — being retired

When to Use

Web applications using the LAMP stack (Linux, Apache, MySQL, PHP)
WordPress, Drupal, and other MySQL-based applications
E-commerce platforms running on MySQL

4. Azure Database for PostgreSQL

What Is It?

Azure Database for PostgreSQL is a fully managed PostgreSQL database service, built on the popular open-source PostgreSQL engine.

Key Features

Feature	Detail
Engine	PostgreSQL (versions 11 through 16)
Extensions	Supports popular PostgreSQL extensions
High availability	Zone-redundant HA
Backups	Automated, up to 35-day retention
Intelligent Performance	Query performance recommendations
Flexible Server	Latest recommended deployment option

When to Use

Applications built on PostgreSQL (Django, Ruby on Rails, etc.)
Geospatial applications (PostGIS extension support)
Complex queries and analytics on relational data

5. Azure Cosmos DB

What Is It?

Azure Cosmos DB is Microsoft's globally distributed, multi-model NoSQL database service. It is designed for applications that require:

Global scale
Single-digit millisecond response times
Flexible data models

Key Characteristics

Feature	Detail
Global distribution	Replicate data to any number of Azure regions — 1 click
Multi-model	Choose your data model and API
Latency	<10ms reads, <15ms writes at 99th percentile
Availability SLA	99.999% (five nines)
Consistency levels	5 levels — from Strong to Eventual
Serverless option	Pay per request, no capacity to manage

Supported APIs (Data Models)

API	Data Model	Use Case
NoSQL (Core SQL)	Documents (JSON)	General purpose NoSQL
MongoDB	Documents	MongoDB compatibility
Cassandra	Wide columns	Large-scale columnar data
Gremlin	Graph	Social networks, recommendation engines
Table	Key-value	Azure Table Storage migration

Cosmos DB Consistency Levels

Cosmos DB offers 5 consistency levels — a tradeoff between consistency and performance:

Strong      →  Highest consistency, highest latency
Bounded Staleness →  Reads lag behind writes by configured amount
Session     →  Consistent within a single client session (most common)
Consistent Prefix →  Reads never see out-of-order writes
Eventual    →  Lowest consistency, lowest latency, highest throughput

When to Use Cosmos DB

Global applications needing data close to users worldwide
Applications requiring <10ms response times at any scale
IoT applications with massive write volumes
E-commerce, gaming, social media at planet scale
Applications currently using MongoDB wanting managed cloud hosting

Database Services Comparison

Service	Type	Engine	Best For
Azure SQL Database	Managed SQL	SQL Server	Cloud-native SQL apps
SQL Managed Instance	Managed SQL	SQL Server	Lift-and-shift SQL Server
Azure Database for MySQL	Managed SQL	MySQL	MySQL-based web apps
Azure Database for PostgreSQL	Managed SQL	PostgreSQL	PostgreSQL apps
Azure Cosmos DB	Managed NoSQL	Multi-model	Global, low-latency apps

Key Decision Guide

Migrating SQL Server with minimal changes?  → SQL Managed Instance
Building new cloud-native SQL app?          → Azure SQL Database
Running WordPress or PHP/MySQL app?         → Azure Database for MySQL
Using Django or Rails with PostgreSQL?      → Azure Database for PostgreSQL
Need global scale, <10ms, NoSQL?            → Azure Cosmos DB

Quick Recap

Azure SQL Database      → Managed SQL Server (PaaS)
SQL Managed Instance    → Near-complete SQL Server compatibility
Azure DB for MySQL      → Managed MySQL
Azure DB for PostgreSQL → Managed PostgreSQL
Azure Cosmos DB         → Global NoSQL, multiple APIs, 5 nines SLA

Official References

Next Chapter → Chapter 13: Azure Identity Services