Expertise level: Advanced
The only way to properly test an OS upgrade is to replicate your server's environment. This can be done on a virtual machine (VM) if purchasing a second server is not ideal for your budget. It's important to remember a VM's performance might not be as quick as the original server but can still be a valid test environment. You can also quickly deploy a cloud server and decommission it after all testing is complete for a budget-friendly test environment: https://kb.iweb.com/hc/en-us/articles/230247408
If your original OS is already on a Cloud server, simply clone your environment: https://kb.iweb.com/hc/en-us/articles/230247668-Live-Cloning-a-cloud-server
If your original OS is on a dedicated server, you need to replicate the environment as precisely as possible on a new server. If you don't use a VM and opt for another dedicated server (more accurate testing) be sure to:
- Install the same current OS and all software
- Apply the OS upgrade
- Test the OS as well as all software for compatibility, bugs and usability
If successful, you will likely not encounter problems if you upgrade the OS on your original server (production environment).
Windows Server upgrades are not recommended by Microsoft. They recommend to reinstall the OS completely instead of upgrading https://kb.iweb.com/hc/en-us/articles/230242228-Purchasing-Guidelines-Windows-Licensing
The Ubuntu community supports OS upgrades: https://kb.iweb.com/hc/en-us/articles/230242128-Upgrading-Ubuntu-OS
The CentOS community does NOT support major OS upgrades.