First, when considering this migration, it is necessary to understand how the database is offered in the Cloud and its differences between on-premise.
While on-premise, in addition to purchasing the hardware-based license, the company needs to take care of several issues, such as how many accesses will be made to the database, the number of connected physical machines, whether it will be in a physical or virtualized environment, how many processors will be running inside the server, among other technical points.
In the Cloud, it is possible to eliminate all this complexity, since the database is offered as a PaaS model, platform as a service, in which for the entire configuration it will only be necessary to stipulate the monthly fee paid to the provider.
The management of the database is also different, while on site, the company performs all the necessary care, in the Cloud, the company will not have free access to the operating system because it is a supplier platform. That way, you won't have as much freedom to make changes.
However, the main point to be considered is licensing. In the on-premise, it is necessary to license all the processors in the cluster, which is a very complex task or to buy datacenter or enterprise licenses with very high values and with a direct impact on the company's cash flow.
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In practice, this happens as follows: suppose that the same database is doing a replication on two different physical machines, which are separate but connected to each other. The company will need to license all processors in the cluster, not just one. There will be different licenses with a minimum number of licenses for each of these machines, which may vary. In the case of some databases, such as SQL Server, for example, if they are on physical machines there will be 2 licenses, now if they are in a virtualized environment there will be at least 4 licenses.