Linux AMI Virtualization types

Linux Amazon Machine Images use one of two types of virtualization:

a) Paravirtual (PV)

b) Hardware virtual machine (HVM).

The main difference between PV and HVM AMIs is the way in which they boot and whether they can take advantage of special hardware extensions (CPU, network, and storage) for better performance.

For the best performance, we recommend that you use current generation instance types and HVM AMIs when you launch your instances.

HVM AMIs

HVM AMIs are presented with a fully virtualized set of hardware and boot by executing the master boot record of the root block device of your image. This virtualization type provides the ability to run an operating system directly on top of a virtual machine without any modification, as if it were run on the bare-metal hardware. 

HVM guests can take advantage of hardware extensions that provide fast access to the underlying hardware on the host system. HVM AMIs can take advantage of enhanced networking and GPU processing. (In order to pass through instructions to specialized network and GPU devices, the OS needs to be able to have access to the native hardware platform; HVM virtualization provides this access)

All current generation instance types support HVM AMIs. The CC2, CR1, HI1, and HS1 previous generation instance types support HVM AMIs.

To find an HVM AMI, verify that the virtualization type of the AMI is set to HVM, using the console or the describe-images command.

PV AMIs

PV AMIs boot with a special boot loader called PV-GRUB, which starts the boot cycle and then chain loads the kernel specified in the menu.lst (menu.lst -> ./grub.conf) file on your image. Paravirtual hosts cannot take advantage of special hardware extensions such as enhanced networking or GPU processing. 

The C3 and M3 current generation instance types support PV AMIs. The C1, HI1, HS1, M1, M2, and T1 previous generation instance types support PV AMIs.

To find a PV AMI, verify that the virtualization type of the AMI is set to paravirtual, using the console or the describe-images command.

PV on HVM

Paravirtual guests traditionally performed better with storage and network operations than HVM guests because they could leverage special drivers for I/O that avoided the overhead of emulating network and disk hardware, whereas HVM guests had to translate these instructions to emulated hardware. 

Now these PV drivers are available for HVM guests, so operating systems that cannot be ported to run in a paravirtualized environment (such as Windows) can still see performance advantages in storage and network I/O by using them. With these PV on HVM drivers, HVM guests can get the same, or better, performance than paravirtual guests.

AMI Launch Permissions

Public - Launch permission to all

Explicit - Launch permission to special AWS accounts

Implicit - Only owner can launch

How are you charged AMI Launch Permissions

With Instance store AMI every time you customize  and create new one all the parts are stored in Amazon S3 for each AMI. So storage footprint for each customized AMI is full size of AMI.

For EBS backed AMI each time you customize and create new one only the changes are stored  for subsequent AMI. resulting in low storage.

We can convert instance store AMI to EBS backed AMI but lot of steps need to be followed.

Copying of AMI is not chargeable.

launch pemrission, user defined tags or s3 permission or not copied from source AMI  o new AMI.

Making AMI public will take some time and available only to that region.

You can create boot strap script to  customize your AMI  to install software on startup