Amazon Relational Database Service
Amazon Relational Database Service or Amazon RDS is a distributed relational database service by Amazon.com. It is a web service running "in the cloud" and provides a relational database for use in applications. It is aimed at simplifying the set up, operation, and scaling a relational database. Complex administration processes like patching the database software, backing up databases and enabling point-in-time recovery are managed automatically. Scaling storage and compute resources can be performed by a single API call. Amazon RDS was first released on 22 October 2009 supporting MySQL databases. This was followed by Oracle Database in June 2011,  Microsoft SQL Server in May 2012 and PostgreSQL in November 2013.
Amazon RDS offers different features to support different use cases. Some of the major features are:
Multi AZ deployment
Multi-Availability Zone deployments are targeted for production environments. Multi-AZ deployments aim to provide enhanced availability and data durability for MySQL instances. When a database instance is created or modified to run as a Multi-AZ deployment, Amazon RDS automatically provisions and maintains a synchronous “standby” replica in a different Availability Zone (independent infrastructure in a physically separate location). In the event of planned database maintenance or unplanned service disruption, Amazon RDS automatically fails over to the up-to-date standby, allowing database operations to resume without administrative intervention.
Multi-AZ RDS instances are optional and have a cost associated with them. When creating your RDS instance, the user is asked if they would like to use a Multi-AZ RDS instance.
Read Replicas use MySQL’s native, asynchronous replication functionality. Read Replicas are aimed at helping to scale out beyond the capacity constraints of a single DB Instance for read-heavy database workloads. They can also be used for serving read traffic when the primary database is unavailable.
Amazon RDS instances are priced very similarly to Amazon Elastic Compute Cloud (EC2). RDS is charged per hour and come in two packages: On-Demand DB Instances and Reserved DB Instances. On-Demand instances are at an ongoing hourly usage rate. Reserved DB Instances require an up-front, one-time fee and in turn provide a discount on the hourly usage charge for that instance.
Apart from the hourly cost of running the RDS instance, users are charged for the amount of storage provisioned, data transfers and Input and Output operations performed. AWS have introduced Provisioned Input and Output Operations, in which the user can define how many IO per second is required by their application. IPOS can contribute significant cost to the total cost of running the RDS instance.
Database instance types
As of April 2014, Amazon RDS supports nine DB Instance Classes, to support different types of workloads: 
|Instance Type||vCPU||ECU||Memory (GiB)||EBS Optimized||Network Performance|
Competitors and alternatives
Several other vendors provide cloud database services similar to Amazon RDS. Oracle offers Oracle Cloud, a database service supporting Oracle's database technology. Microsoft offers Windows Azure SQL, a service supporting the Microsoft SQL database. Competitors supporting MySQL include RackSpace Cloud Databases , Google Cloud SQL, HP Cloud for MySQL, Xeround Cloud Database, and ClearDB.
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