"Wanted: a framework for building available services on the cloud"
Kiran-Kumar Muniswamy-Reddy, Harvard School of Engineering and Applied Sciences

Many of the services provided by cloud providers are designed to be
highly available.  Extending the services to provide some additional
functionality, however, is hard as any extension service that a user
builds and deploys cannot be as available as the services provided by
the cloud provider.  For example, AWS S3 provides a simple PUT/GET
interface for objects.  S3 is designed by Amazon to be highly
available.  We wanted to use S3 as a back-end, but we also needed to
ensure consistency across multiple objects, i.e., either all the
objects are stored or none of them are stored.  One simple solution
for this would have been deploy a service on EC2 instances that
ensures multi object consistency.  EC2, however, is not as highly
available as S3.  Luckily, we could get around this by coupling S3
with another AWS service, Simple Queuing Service (SQS), to ensure both
multi-object consistency and availability.  Another example is
Vertica's on-demand cloud version that is hosted on AWS EC2.  The
on-demand service provides automatic scaling, replication, failover,
and recovery.  Vertica presumably had to build a service on EC2
instances that ensured all these properties.

While the current cloud services are being built with the correct
abstractions, many users will end up developing their own solutions to
take advantage of the availability that cloud services promise.  Cloud
companies can actually fill this gap for the users by providing
frameworks that reduce the time to build available services.  One
example is RightScale, a company that allows customers to build
scalable and reliable customer facing websites and batch processing
back-ends on the cloud.  The cloud, however, is not limited to hosting
websites and batch processing jobs.  Furthermore, if the cloud
providers themselves solve the problem, it will result in reduced
pricing for users.  For example, if we had used EC2 instances to
provide a transactional interface to S3 that is also highly available,
the cost would have been an order of magnitude higher than just using
S3. A cloud provider, on the other hand, might be able to provide the
same features at a lower cost by amortizing the cost across many
services.  If, indeed the cloud services provided a framework for
building available services, the questions are: What applications
should the framework cater to? What are the appropriate knobs to
expose to users?