Cloud Databases

What Are Cloud Databases?

Cloud databases are managed database services run by a cloud provider — they handle provisioning, patching, backups, and failover for you. This page deliberately covers the landscape across providers, not one vendor in isolation, because the decision engineers actually face is "which managed database fits this workload," not "how does one specific service work."

The Landscape, Compared

Provider	Relational (managed)	NoSQL (managed)	Best known for

|---|---|---|---|

AWS	RDS (Postgres/MySQL), Aurora	DynamoDB	Broadest ecosystem, Aurora's storage-compute separation
Azure	Azure SQL Database, Azure Database for PostgreSQL	Cosmos DB	Cosmos DB's multi-model, multi-region writes
GCP	Cloud SQL, AlloyDB	Firestore, Bigtable	Spanner's globally-consistent relational scale
Vendor-neutral	Self-managed Postgres/MySQL on any VM	MongoDB Atlas, Redis Cloud	Full control, portability across clouds

Why "Managed" Matters

•No patching/upgrades — the provider handles OS and database engine patches.

•Automated backups & point-in-time restore — built in, not something you script yourself.

•Multi-AZ failover — a standby replica takes over automatically during an outage, usually in under a minute.

•Read replicas — scale read-heavy workloads without re-architecting the app.

Choosing Relational vs NoSQL (Managed)

•Need ACID transactions, joins, well-understood schema → managed relational (RDS/Aurora, Cloud SQL, Azure SQL).

•Need massive horizontal scale, flexible schema, single-digit-millisecond latency at huge scale → managed NoSQL (DynamoDB, Cosmos DB, Firestore).

•Need global write scale with strong consistency → Spanner or Cosmos DB (multi-region writes) — a genuinely distinct category from single-region relational.

Cost Model Basics

Cloud databases are billed on a mix of: compute (instance size or "capacity units"), storage (per GB-month), I/O/requests, and data transfer. NoSQL services like DynamoDB additionally offer on-demand (pay-per-request) vs provisioned (reserved throughput) pricing — on-demand is simpler for unpredictable traffic, provisioned is cheaper for steady, predictable load.

Migration Considerations

Moving from a self-managed database to a cloud-managed one usually means: schema compatibility checks (especially Oracle/SQL Server → Postgres/MySQL), a data migration tool (AWS DMS, Azure Database Migration Service), and a cutover strategy (big-bang vs. dual-write during transition).

💡 When to specialise

Once you've picked a primary cloud provider for a project, it's completely reasonable to go deep on that provider's specific service (e.g. DynamoDB) — this page is the "compare before you commit" step, not a replacement for vendor-specific deep dives.

Cloud Databases — Overview