These days, enterprises are moving massive numbers of applications to the cloud in a process called "lift and shift." That means transporting the code and the data, recompiling it, doing a bit of testing, and moving on.
The trouble with this approach is that many -- and I mean many -- enterprise applications need a whole lot of improvements to work well in the cloud. They are not properly designed for the cloud (the data is too coupled with the logic), there are systemic performance problems, their security is lacking ... take your pick.
Somehow, enterprise IT often believes that when these applications are moved from an on-premises platform to a public cloud provider, these issues will magically go away. Nope.
As I've said in my cloud architecture talks over and over again: Bad applications moved to the cloud will be bad applications in the cloud. You have the same problems you had before, plus new ones caused by the poor fit to the cloud.
Moreover, because you will now pay for the resources as they are consumed by the applications, you could have a big cloud bill in your future.
The reality is you need to fix or refactor applications destined for the cloud. My advice is to always consider the platform where the applications will reside -- typically, a PaaS or IaaS cloud -- then change the underlying application design to take advantage of that platform. This is what makes an application cloud-native.
Although most enterprises are reluctant to spend the money to redesign and rebuild applications, that fact is you'll spend the money anyway: If you do not use your public cloud resources effectively, you'll pay more to operate the applications. That accumulated cost is usually much higher than the cost of refactoring an application in the first place.
The right way to migrate applications is to fix it before you move it to the cloud. Don't listen to anyone -- even cloud providers -- who tells you this work is unnecessary. If you follow that bad advice, you'll simply kick the can further down the road. Eventually, you have to deal with it -- at which point your cost will be much higher.