The simplest way to obtain a virtual machine image that works with OpenStack is to download one that someone else has already created. Most of the images contain the cloud-init package to support the SSH key pair and user data injection. Because many of the images disable SSH password authentication by default, boot the image with an injected key pair. You can SSH into the instance with the private key and default login account. See the OpenStack End User Guide for more information on how to create and inject key pairs with OpenStack.
The CentOS project maintains official images for direct download.
In a CentOS cloud image, the login account is centos.
CirrOS is a minimal Linux distribution that was designed for use as a test image on clouds such as OpenStack Compute. You can download a CirrOS image in various formats from the CirrOS download page.
If your deployment uses QEMU or KVM, we recommend using the images in qcow2 format. The most recent 64-bit qcow2 image as of this writing is cirros-0.3.4-x86_64-disk.img.
In a CirrOS image, the login account is cirros. The password is cubswin:).
Canonical maintains an official set of Ubuntu-based images.
Images are arranged by Ubuntu release, and by image release date, with current being the most recent. For example, the page that contains the most recently built image for Ubuntu 14.04 Trusty Tahr is http://cloud-images.ubuntu.com/trusty/current/. Scroll to the bottom of the page for links to the images that can be downloaded directly.
If your deployment uses QEMU or KVM, we recommend using the images in qcow2 format. The most recent version of the 64-bit QCOW2 image for Ubuntu 14.04 is trusty-server-cloudimg-amd64-disk1.img.
In an Ubuntu cloud image, the login account is ubuntu.
Red Hat maintains official Red Hat Enterprise Linux cloud images. A valid Red Hat Enterprise Linux subscription is required to download these images.
In a RHEL cloud image, the login account is cloud-user.
The Fedora project maintains a list of official cloud images at https://getfedora.org/cloud/download/.
In a Fedora cloud image, the login account is fedora.
SUSE provides images for openSUSE. For SUSE Linux Enterprise Server (SLES), custom images can be built with a web-based tool called SUSE Studio. SUSE Studio can also be used to build the custom openSUSE images.
Since January 2015, Debian provides images for direct download. They are now made at the same time as the CD and DVD images of Debian. Therefore, images are available on each point release of Debian. Also, weekly images of the testing distribution are available.
In a Debian image, the login account is debian.
As of this writing, we are not aware of other distributions that provide images for download.