Designing the most suitable Azure infrastructure for running SAP workloads is very much dependent on the size and nature of the SAP workloads. Ascertaining and documenting your prospective target landscape requirements is the first step in a well structured migration plan. Once you understand in detail what is required, you can make decisions about the power and nature of compute resources, like the number of virtual machines needed, along with the amount of disk storage. The size and type of your target database or databases, along with the SAP version, NetWeaver or S/4HANA, will have a significant impact on infrastructure and operating system choices. In the case of a large HANA installation, you may need a bare metal large instance with the associated particular infrastructure in file storage and ExpressRoute networking. In this case, you are limited to SUSE or Red Hat Linux distributions. Virtual machines will need to be in proximity placement groups to maintain low latency network connections. You will know your high availability and disaster recovery parameters so you can choose the most appropriate levels of replication and redundancy. You can decide to protect your system against host hardware failure right through to the unlikely event of a whole Azure region going down. Most SAP deployments are multi-node affairs with an on-premises component. This means implementing high-performance networking using features like ExpressRoute Gateway FastPath and Global Reach. While ExpressRoute is essentially a private network, you can deploy Azure Application Gateway as a performant and secure entry point when you open your SAP system up to internet traffic. 

When it comes to deploying the SAP applications and databases on Azure infrastructure, it is possible to have multiple databases or apps on one host. SAP has several database multi-hosting or stacking models in the form of Multiple Components on One Server or Database, MCOS, and MCOD. Central Services can also be stacked on a single host, and SAP Fiori can share a HANA database when used exclusively with S/4HANA. Multi-hosting, where it doesn't impact performance, can save costs, especially in a non-production environment. A virtual infrastructure can throw up some unexpected issues, and a good example is the impact of virtual hardware identification in the context of SAP license validation. SAP has added the unique virtual machine ID as part of the hardware key generation, and for the most part, it shouldn't be an issue. Still, under specific circumstances, the virtual hardware can change, rendering the license invalid—just something to watch out for.