"These applications usually weren't built for the cloud, with much of their architecture relying on vertical scaling and infrastructure-level resiliency. With traditional single-cloud provider models, enterprises often must choose whether to invest in expensive rewrites or compromise performance with a more simplistic deployment method," the report warned.
The researchers surveyed 500 businesses that were early cloud adopters, having moved nearly half (44 percent) their applications to the cloud, on average, and planning to increase that to almost two-thirds (62 percent) in the next two years.
While the earliest cloud adopters attempted a mass migration of all applications, this strategy has now been replaced with an app-by-app approach, or migrating batches of related applications.
"While many businesses associate the cloud with cost savings, underestimating the resources involved in cloud migration can quickly cause costs to spiral out of control," said the Cloud Migration: Critical Drivers for Success report, which was commissioned by Virtustream.
App usage patterns
One issue is relatively well known: cloud services are most cost effective for applications with usage peaks, such as a system that's only used once a month. Using the cloud for these kinds of apps may make more sense than having servers sitting unused for long periods. However, the economics make less sense for applications with a predictable requirement for computing power.
"Public cloud platforms reward variable usage, scaling up and down depending on your requirements and the way you setup the resources. Consistent usage is not rewarded with discounting," the report said.
Almost half of organisations surveyed said they spent over $1m on staff and technology costs to migrate mission-critical apps to the cloud.
"People and tools needed to move the applications to their new platform generate significant additional costs. Cost challenges related to migration come in many different forms, some less obvious than others," the report said.
Among the top cost issues was the need to rewrite applications to optimise them for the cloud -- especially ones that are very complex or have a high degree of customization. The cost of passing data between the cloud and corporate data centers is often overlooked in migration planning, and one-third of early migrators cited high fees for passing data between systems as a challenge in moving their mission-critical applications.
The report also found that migration skills are rare and expensive: almost half (47 percent) of early migrators said they have teams of more than 50 people dedicated to their migration strategy and process.
"The skills required for migration are both difficult and expensive to find, as they are in high demand and must often be brought in from the outside or trained up at significant time and expense. Once there, keeping the talent from vendors with deep pockets is challenging," said the report.
To back this up, the report quotes the VP of IT infrastructure at one global enterprise bank: "We thought we had the skills to address our cloud migration, but at the end of the day, we really did not. We ended up adding about six to eight months to our migration to train folks on the job to complete the work, and it sent our costs through the roof," he said.
One in three respondents also warned that their software database license costs drastically increased if they moved applications.
Performance was also highlighted as another issue. Nine out of ten respondents said they had problems with the performance of their critical applications during and after migration, while one in three said they would not move some critical applications due to a potential decline in performance.
Latency between on- and off-premises applications and problems due to dependencies on applications not in the cloud were also issues for nearly half of the survey's respondents.