The OpenStack Image service (Glance) provides the functionality that allows OpenStack users to manipulate virtual machine images. Users can discover virtual machine images, upload new images, and also launch a VM from an existing image. Glance also provides a REST API which is consumed by the Glance command-line utility.

The Image service has an API service and a registry service. Both are required for Glance to work properly. It also uses a backend database that is either MySQL or postgres. It supports storage backends where the actual virtual machine images are stored. The backend to be used is configurable in the glance-api.conf file.

The Glance service doesn't often need any troubleshooting and it doesn't perform any complex operations. However, as an administrator, we should be aware of the basics.

By default, the Image service writes its log files in the following directory:

/var/log/glance/

You may have to turn on the logging level in the file, /etc/glance/glance-api.conf by setting the debug flag to true:

debug = true

In this directory, there are many log files. The api.log file likely has error messages that provide a hint to the root cause. You may also need to check the Keystone logs, as Glance uses Keystone for authentication.