AWS: Dedicated Host Vs Dedicated Instance

Photo by Belle Co

AWS provides two different types of dedicated virtualization - 

• At the host level 
• At the instance level. 

The post attempts to illustrate the differences between the two offerings.

Dedicated Host

A dedicated host comprises physical hardware dedicated to a single account. A dedicated host can run instances of varying sizes that belong to a single instance type. The number of instances is limited to the number of cores available on the host.

A dedicated host can be shared among multiple organizations or accounts.

BYOL

Software licenses are often pegged on the number of CPUs, cores, and sockets. 

A dedicated host provides visibility into the number of cores utilized by each deployed instance. It is, therefore, possible to directly determine if licenses are being correctly used. This makes it one of the main reasons for obtaining a dedicated host.

License management can be further simplified by using AWS License Manager, automatically tracking licenses when AMIs belonging to a license group are launched.

Host Affinity

You can target a dedicated host by specifying its host id when launching an instance. This ensures host affinity upon instance restarts.

Restrictions

AMIs

Certain OSes and SQL Server require you to provide your own AMI, and AWS's AMIs are incompatible with dedicated hosts.

Host Limit

There is a soft limit of 2 dedicated hosts per family per region, but it can be increased.

RDS

AWS Relational DB Service cannot be launched on Dedicated Hosts

ASG.

Auto Scaling Group Instances targeting a Dedicated Host need to be launched via a Launch Template.

Dedicated Instance

You are guaranteed that the Dedicated Instance will be launched in physical hardware dedicated to your account, and it will not contain instances belonging to other accounts. However, a dedicated instance does not show how many underlying cores are utilized.

Host Affinity

A Dedicated Instance may or may not be instantiated on the same physical hardware upon restart. However, the underlying physical hardware is guaranteed to only contain instances belonging to the same account.

Sources

https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/dedicated-hosts-overview.html

https://www.youtube.com/watch?v=kukiDf9Ilcc