AWS

Tenancy options

Tenancy options are the ways you can have resources dedicated to your instances.

1. Shared Tenancy. Your instance runs on the same host machine with other accounts.
2. Dedicated Instance. A host machine will be dedicated to the customer's account. Your Dedicated Instance will run in the host with your other instances. The Dedicated Instance will have more resources dedicated to it.
3. Dedicated Host. A physical server will be launched for the customers. Addresses licensing issues. Gives the customer granular control of its resources.

Placement groups

Placement groups are the way instances are arranged on physical racks.

1. Cluster. All instances are placed in the same partition of one AZ. This means that they sit in the same rack. The instances would have improved performance between them for being close in proximity. But they share the same power hardware risks.
2. Partition. Instances are isolated in partitions that sit on different racks. This is applicable for sharded databases and data warehouses where data is replicated for high availability. This placement group is fault tolerant to hardware failure.

Can be placed in multiple AZ in the same Region.

3. Spread. All instances run on unique hardware. Max of 7 instances per AZ.

Azure

Azure has Dedicated Hosts as well.

More granular tenancy models are applicable for SaaS applications.

It also has Proximity Placement Groups for its VMs. This is similar to the AWS Cluster.