Operating System And Databases
The most common operating systems IaaS vendors support are Ubuntu, CentOS, and Red Hat Enterprise Linux, as well as Windows Server 2003 and 2008. In general, supporting tools and libraries for automation and orchestration tend to be implemented for Linux before Windows, but it's far more common to see extensive Windows deployments on IaaS now than a few years ago.
Some IaaS vendors offer specialized VMs that come with both operating system and database server installed and include simple API-driven methods for backing up and restoring data to and from the database server. These can be very useful for quickly implementing an application in the cloud without having to spend a lot of time on software installation, configuration, and orchestration.
The downside to these services is that you pay for convenience--they're more expensive than running the exact same software on the exact same hardware on the IaaS provider's systems. They also limit your ability to fine-tune some or all configuration options.
You may find a cloud management or configuration management software or service that has database templates built for your IaaS vendor to be a better and less costly option. For example, RightScale offers a Database Manager ServerTemplate that provides a similar feature set to Amazon RDS but lets customers run database deployments across multiple clouds and doesn't have Amazon RDS's hourly price premium. Cloud management platform enStratus is working on a library of Chef and Puppet scripts that will enable similar functionality.
The utility pricing that most IaaS vendors offer can seem very low, but like a cellphone bill, lots of little charges can add up. PlanForCloud .com is a useful resource for cost planning, letting you design a complete cloud architecture and compare costs among IaaS providers.
The most important part of estimating costs is making sure you're comparing apples to apples. Most providers have a one-core, 1- to 2-GB RAM virtual machine available for between 8 cents and 10 cents per hour with on-demand pricing. If you can take advantage of a provider's discount plan (commit to purchase a certain amount of computing resources or pay a lump sum up front to obtain lower hourly pricing for one or more years), you'll see significant savings--up to and beyond 40% with Amazon and Terremark.