Azure Cosmos DB is a fully managed NoSQL database service for modern app development. Get guaranteed single-digit millisecond response times and 99.999-percent availability, backed by SLAs, automatic and instant scalability, and open-source APIs for MongoDB and Cassandra.

Amazon Aurora Serverless is an on-demand, auto-scaling configuration for Amazon Aurora. It automatically starts up, shuts down, and scales capacity up or down based on your application's needs. It enables you to run your database in the cloud without managing any database capacity.

With Aurora Serverless, you simply create a database endpoint, optionally specify the desired database capacity range, and connect your applications. You pay on a per-second basis for the database capacity you use when the database is active, and migrate between standard and serverless configurations with a few clicks in the Amazon RDS Management Console.

Example Pricing

10M Serverless Request Units ($2,82), 10GB of consumed storage ($2,5), 10 GB of backup storage ($1,5) $6,82USD 

A wide variety of payment methods exist, with the smallest database starting at an upfront $243, or $24.82 monthly for a year.

​Onboarding
Great documentation to start things off.

​Scalability

Includes the ability to autoscale, with configuration options for it.

Regions

Azure Cosmos DB is available on all the platforms that have Azure available, such as the United States, Europe, Asia Pacific, and more to come.

​Backups 

Azure Cosmos DB automatically takes backups of your data at regular intervals. The automatic backups are taken without affecting the performance or availability of the database operations. Azure Cosmos DB automatically takes a full backup of your database every 4 hours and at any point of time, only the latest two backups are stored by default. If the default intervals aren't sufficient for your workloads, you can change the backup interval and the retention period from the Azure portal.

​Security
If you choose an on-premises solution, you need to provide everything from end-point protection to physical security of your hardware - which is no easy task. If you choose a PaaS cloud database provider such as Azure Cosmos DB, your area of concern shrinks considerably.

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Onboarding
Good documentation that includes tutorials.

Scalability
On-demand auto scaling configuration, sharding.

Regions
US, Africa, Asia Pacific, China, South America, Middle East and Europe. The support varies across specific versions of each database engine, and across AWS Regions.

 
Backups 
Aurora backs up your cluster volume automatically and retains restore data for the length of the backup retention period. You can specify a backup retention period, from 1 to 35 days, when you create or modify a DB cluster.  Aurora backups are stored in Amazon S3.

Security
By default, Aurora Serverless v1 uses the Transport Layer Security/Secure Sockets Layer (TLS/SSL) protocol to encrypt communications between clients and your Aurora Serverless v1 DB cluster. It supports TLS/SSL versions 1.0, 1.1, and 1.2.

Azure Cosmos DB is a fully managed NoSQL database for modern app development. Single-digit millisecond response times, and automatic and instant scalability, guarantee speed at any scale.

• ​Guaranteed speed at any scale
  
• Fast, flexible app development with SDKs for popular languages, a native Core (SQL) API along with APIs for MongoDB, Cassandra, and Gremlin, and no-ETL (extract, transform, load) analytics
  
• Ready for mission-critical applications
  
• Fully managed and cost-effective serverless database
  
• Serverless database operations
  
• Hybrid platform for Cassandra data
• No-ETL analytics over real-time operational data 
  
  

• Compatible with MySQL and PostgreSQL
  
• High-performance storage subsystem
  
• Automates and standardizes database clustering and replication
• Supports the full breadth of Aurora features, including Global Database, Multi-AZ deployments, and read replicas.
  
• Takes advantage of the familiar Amazon Relational Database Service (Amazon RDS) features for management and administration.