Though explaining cloud computing is not in the scope for this book, I will explain it in just one paragraph. Any business, big or small, needs hardware infrastructure with different software installed on it. An operating system is the basic software needed along with different servers (from the software perspective) for storage, mail, web, database, DNS, and so on. The list of software frameworks/platforms that are needed would end up being large. The point of interest here is that the initial budget for this hardware and software platform is high, and so we are not even considering the real estate needed to host it. This is where cloud computing providers such as Amazon, Rackspace, Google, and Microsoft come into play. They have hosted the high-end hardware and software in different data centers across the globe and let us choose from different configurations to start an instance. This is then accessed remotely over the public network for management purposes. Literally, all our setting up is done in the cloud provider's data center and we just pay as we use. Shut down the instance and you stop paying for it. Not only small start-ups, but large enterprises often temporarily fall back to cloud servers for temporary rise in the computing resource demands. The prices offered by the providers are very competitive too, particularly AWS, and its popularity says it all.

The wiki page, http://en.wikipedia.org/wiki/Cloud_computing, has a lot of details, perhaps a bit too much for someone new to the concept, but is a good read nevertheless. The article at http://computer.howstuffworks.com/cloud-computing/cloud-computing.htm is pretty good and also recommended for you to read if you are not aware of the concept of cloud computing.

In this chapter, we will set up MongoDB instances on the cloud using MongoDB service providers and then by ourselves on Amazon Web Service (AWS).