Cloud database

A cloud database is a database that typically runs on a cloud computing platform. There are two common deployment models: users can run databases on the cloud independently, using a virtual machine image, or they can purchase access to a database service, maintained by a cloud database provider. Of the databases available on the cloud, some are SQL-based and some use a NoSQL data model.

Deployment models

There are two primary methods to run a database in a cloud:

Virtual machine Image

Cloud platforms allow users to purchase virtual-machine instances for a limited time, and one can run a database on such virtual machines. Users can either upload their own machine image with a database installed on it, or use ready-made machine images that already include an optimized installation of a database. For example, Oracle provides a ready-made machine image with an installation of Oracle Database 11g Enterprise Edition on Amazon EC2^[1] and on Microsoft Azure.^[2]

Database as a service (DBaaS)

Some cloud platforms offer options for using a database as a service, without physically launching a virtual machine instance for the database. In such a configuration, application owners do not have to install and maintain the database themselves. Instead, the database service provider takes responsibility for installing and maintaining the database, and application owners pay according to their usage. For example, Amazon Web Services provides three database services as part of its cloud offering: SimpleDB, a NoSQL key-value store; Amazon Relational Database Service, a SQL-based database service with a MySQL interface; and DynamoDB. Similarly, Microsoft offers the Azure SQL Database service^[3] as part of its cloud offering. Oracle also provides its own DBaaS, allowing users to access Oracle Database 11g and 12c as cloud services.^[4][5]

A third option involves managed database-hosting in the cloud, where the cloud database vendor does not offer the database as a service, but hosts the database and manages it on the application owner's behalf. For example, cloud provider Rackspace offers managed hosting for MySQL on dedicated^[6] and cloud architectures^[7] and NoSQL databases via Object Rocket's managed MongoDB service.^[8] Similarly, on Azure^[9] and on Amazon Web Services, MongoLab provides MongoDB-as-a-Service.^[10]

Architecture and common characteristics

• Most database services offer web-based consoles, which the end user can use to provision and configure database instances. For example, the Amazon Web Services web-console enables users to launch database instances, create snapshots (similar to backups) of databases, and monitor database statistics.^[11]
• Database services consist of a database-manager component, which controls the underlying database instances using a service API. The service API is exposed to the end user, and permits users to perform maintenance and scaling operations on their database instances. For example, the Amazon Relational Database Service's service API enables creating a database instance, modifying the resources available to a database instance, deleting a database instance, creating a snapshot (similar to a backup) of a database, and restoring a database from a snapshot.^[12]
• Database services make the underlying software-stack transparent to the user - the stack typically includes the operating system, the database and third-party software used to manage the database. The service provider (e.g. MongoLab or ObjectRocket) is responsible for installing, patching and updating the underlying software stack and ensuring the overall health and performance of the database.
• Database services take care of scalability and high availability of the database. Scalability features differ between vendors - some offer auto-scaling, others enable the user to scale up using an API, but do not scale automatically. There is typically a commitment for a certain level of high availability (e.g. 99.9% or 99.99%).

Data model

It is also important to differentiate between cloud databases which are relational as opposed to non-relational or NoSQL:

SQL databases

Such as PostgreSQL, NuoDB, Oracle Database, Microsoft SQL Server, MariaDB and MySQL, are one type of database which can run in the cloud (either in a Virtual Machine Image or as a service, depending on the vendor). SQL databases are difficult to scale, meaning they are not natively suited to a cloud environment, although cloud database services based on SQL have started to address this challenge.^[13]

NoSQL databases

Such as Apache Cassandra, CouchDB and MongoDB, are another type of database which can run on the cloud. NoSQL databases are built to service heavy read/write loads and can scale up and down easily,^[14] and therefore they are more natively suited to running on the cloud. However, most contemporary applications are built around an SQL data model, so working with NoSQL databases often requires a complete rewrite of application code.^[15]

Vendors

The following table lists notable database vendors with a cloud database offering, classified by their deployment model – machine image vs. database as a service – and data model, SQL vs. NoSQL.

Cloud database vendors by deployment and data model

	Virtual Machine Deployment	Database as a Service
SQL Data Model	IBM DB2[16] Ingres (database)[17] MariaDB[18] [19] MySQL[20] NuoDB[21] Oracle Database[1][22] PostgreSQL[23]	IBM dashDB data warehouse as a service Amazon Relational Database Service Clustrix Database as a Service[24] EnterpriseDB Postgres Plus Cloud Database[25] Heroku PostgreSQL as a Service (shared and dedicated database options)[26] Microsoft Azure SQL Database (MS SQL)[27] Xeround Cloud Database* - MySQL front-end (*service no longer available)[28]
NoSQL Data Model	Apache Cassandra on Amazon EC2[29] Clusterpoint Database Virtual Box VM [30] CouchDB on Amazon EC2[31] Hadoop on Amazon EC2[32] or Rackspace[33] MarkLogic on Amazon EC2[34] MongoDB on Amazon EC2,[35] Microsoft Azure,[36] or Rackspace[37] Neo4J on Amazon EC2[38] or Microsoft Azure[39]	Amazon DynamoDB Amazon SimpleDB Azure DocumentDB Cloudant Data Layer[40] (CouchDB) Google App Engine Datastore MongoDB Database as a Service (several options)[41]

See also

• Cloud computing
• Cloud storage
• Relational database

References

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2. List of Oracle VM Images (MSDN), Retrieved 2014-9-22
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