EC2 Tenancy Models

Here are different types of tenancy model available which we need to select while creating the EC2. Below are the list of models with explanation

a) Shared Tenancy 

The physical Hardware where your EC2 is hosted will be shared with other customers also. Pricing is less as the Hardware is shared with other customer's. When the instance is Stopped and Started the underline physical server will change but  Reboot will not change the underline hardware.

b) Dedicated Instances 

The physical hardware is completely dedicated for you and won't be shared with other customer and only your EC2 instances will be hosted there. In Simple terms, Hardware dedicated for your account. But during start and stop of the server the underline Hardware will change and we may get new dedicated hardware. And your shared instances (same account) wont be launched in the underlying hardware only dedicated instances of particular type will be launched in the same hardware.

For example: Requesting a m4.large dedicated instance could end with your instance on a server exactly the size of an m4.large.

In addition to instance charge of per hour rate an additional of 2$ will be charged per hour per region. This 2$ will be same if it is 10 instance or 1 instance. As it will be charged per hour per region

c) Dedicated Hosts 

Only difference between Dedicated instance and Dedicated host is even after stop & start underlying hardware will not change. This method is useful when we are going for a hardware based license model. Billing will be high as we are using full host.

As we get the complete hosts, irrespective of utilization we will pay the complete charge as the host is dedicated for You. This is bit costlier than others.  

Number of instances per dedicated hosts calculation is available in AWS help page. For example if we select m4 as our dedicated hosts then we can have 22 large m4 or 11 xlarge