It has been over three years since Amazon Web Services introduced its Relational Database Service (RDS). But until now, RDS has ostensibly been in "beta"—available only to a subset of customers. This week, Amazon announced that RDS is generally available. It now supports multiple database types, and customers can get a service-level agreement for their hosted databases if they're mirrored across multiple Amazon "availability zones" (AZs). Amazon is committing to "reasonable efforts" to ensure that multi-AZ RDS instances have at least 99.95 percent uptime.

Facing increased competition from Google's Cloud Platform—which includes the MySQL-based Google Cloud SQL relational database service—Amazon has expanded the types of databases that can be hosted with RDS as well. RDS is now available in three database "flavors": MySQL, Microsoft SQL Server, and Oracle (though the multizone service-level agreement is only available with MySQL and Oracle databases). RDS also now supports "read replicas" within and across availability zones to help scale up applications with high volumes of database reads.

By comparison, Google Cloud SQL includes geographic replication as part of the service but offers no service-level guarantees. At their most basic configurations, the pricing for RDS and Google's Cloud SQL services are very similar—though the different approaches to pricing and instance configurations vary widely based on size and usage levels.