An image defines what will run on a guest instance in your Eucalyptus cloud. An image
contains everything necessary to boot and run an operating system: either one of the Linux
distributions – CentOS, Fedora, Ubuntu, Debian, etc – or one of the supported Windows server
Images of two types are supported by Eucalyptus:
- HVM images are raw disks that can boot independently. They can contain
Linux or Windows operating systems. HVM stands for Hardware-assisted Virtual
Machine because such images can only run efficiently on hardware that supports
virtualization. When an HVM image is uploaded and registered, it becomes a
Eucalyptus Machine Image (EMI) of type "hvm", with a unique ID.
- Paravirtual images are Linux images that can boot if they are paired with
a kernel and ramdisk that are compatible with the host's hypervisor. Currently
only root file system images are supported (on AWS, a paravirtual image can be a
file system or a full disk). When a paravirtual image is uploaded and
registered, it also becomes an EMI of "paravirtual" type, which needs to be
paired with a kernel (EKI) and ramdisk (ERI) images to be usable. EKI contains a
kernel (i.e., the ‘vmlinuz’ file typically found in the /boot directory of a
Linux system). ERI contains the kernel modules (i.e., the ‘initrd’ file from the
Depending on the method used for upload, an instance's disk will reside on one of two types of
- Instance Store - volumes are located on temporary disk space that is destroyed when
instances shut down. These volumes are based on a template residing in Object
Storage. Instance Store can host either HVM or paravirtual images.
- Elastic Block Store (EBS) - volumes are disks with lifetimes that can be independent
of instances. These volumes are based on snapshots of EBS volumes (instead of
templates in Object Storage). Only HVM images can be deployed on EBS in
Eucalyptus (in AWS, EBS can also host paravirtual images).
To help get you started, Eucalyptus provides pre-packaged virtual machine images that are ready
to run in your cloud. You can download them from the Eucalyptus Machine Image catalog. Both HVM and paravirtual
images are available there. Each paravirtual image comes bundled with a corresponding
EKI and ERI.
If you find that the pre-packaged images don't meet your needs, you can migrate an image from
another cloud system (such as Amazon Web Services) or create your own image. See the
rest of this guide for more information.