By now, just about everyone is familiar with the potential benefits of the public cloud, even if they haven't yet decided to leverage it in some way. The elasticity and scalability offered by the cloud combined with pay-as-you-go pricing can be compelling.
However, for heavy cloud users, simply comparing the costs and relative flexibility of running workloads in the cloud versus running them on-premise doesn't tell the whole story. Potential users must consider how they're actually going to get access to the systems that reside in the cloud -- especially in relation to hybrid cloud and storage-intensive applications.
Typically, businesses will use the public Internet to get where they need to go, but this can be an expensive and technically challenging way to secure high-quality access to cloud-hosted resources. To answer this challenge, cloud service providers are increasingly offering direct connections into their networks, with Amazon's Direct Connect as one of the more mature options.
The Internet connectivity challenge
Let's say you've decided to leverage Amazon's S3 and Glacier services to provide offsite backups for your on-premise network. This is a popular use case for cloud storage that combines nearly limitless scalability, very high data durability, and the elimination of a big chunk of backup/recovery capital expense. Assuming you have a decent-sized connection, your current on-premise Internet pipe will probably work well for relatively small amounts of data. A 100Mbps Internet connection, for example, will handle 40GB to 45GB per hour at full utilization.
If you work with large image-based backups (say, of a virtualized environment) or simply have a lot of data to move, that relatively large circuit may not be anywhere near big enough to transfer each night's full data load to the cloud. Additionally, if you use a commodity Internet connection, your traffic is almost sure to be routed through a few different ISPs before it reaches the AWS network -- bumping up latencies and potentially restricting your throughput due to congestion. If you decide to ship backups to the cloud all day long (say, by using a caching cloud appliance like Amazon's Storage Gateway), you may also have to implement QoS on your Internet circuit to prevent normal Internet traffic from being crowded out by your backups.
On top of all of this, "commodity" Internet access (especially with high-quality Tier 1 providers) can be surprisingly expensive -- often costing two or three times as much as a point-to-point circuit of similar bandwidth. Even after you've routed the necessary bandwidth to your premise, you could find yourself paying a hefty sum for Internet transfer from your cloud service provider. For example, while Amazon doesn't charge you for moving data onto its network, it'll run you 12 cents per gigabyte for pulling data out of its network. That doesn't seem like much at first, but it can add up if you pull a lot of data out of the cloud.