Hi @Deni Garo ,
To add to what Rafael has suggested, I will start with determining your VM size requirements based on the expected volume of authentication requests. Use the specifications of the machines hosting AD DS on premises as a starting point, and match them with the Azure VM sizes. Once deployed, monitor utilization and scale up or down based on the actual load on the VMs.
Check this initial planning guide - capacity-planning-for-active-directory-domain-services
Create a separate virtual data disk for storing the database, logs, and sysvol folder for Active Directory. Don't store these items on the same disk as the operating system. By default, data disks that are attached to a VM use write-through caching. However, this form of caching can conflict with the requirements of AD DS.
Configure the VM network interface (NIC) for each AD DS server with a static private IP address for full domain name service (DNS) support.
If the new deployed Domain Controllers (DC) VMs will have also the role of DNS servers, it's recommended to configure them as custom DNS server at the Azure Virtual Network level
The only scalability consideration is to configure the VMs running AD DS with the correct size for your network load requirements, monitor the load on the VMs, and scale up or down as necessary.
Hope this helps.
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