Eucalyptus Versions: 4.0
Restarting Image Worker Instance After Forcing Image Worker Instance Termination
The Image Worker instance is a service that does the following:
- Provides support mechanism for ImportVolume  and ImportInstance 
- Converts Instance Store-Backed Paravirtual EMIs to Instance Store-Backed HVM instances when launched.
When any of these actions are done for the first time on a Eucalyptus 4.0 cloud, an Image Worker instance is launched, and will stay running until it is manually terminated.
There are certain situations when the cloud administrator needs to terminate all instances running on the cloud. These situations could include the following:
- Non-Eucalyptus Patch Updates on machines that need to be rebooted (i.e. kernel updates)
- Changing between networking modes (e.g. Managed to Managed-NOVLAN, Managed to Edge, etc.)
Since the Image Worker instance is actually an instance part of an AutoScaling group , to terminate it, the cloud administrator needs to update following attributes of the autoscaling group to 0:
- --max-size - maximum group size
- --min-size - minimum group size
- --desired-capacity - number of running instances the group should contain
An example of this being updated with the euscale-update-auto-scaling-group  command is as follows:
$ euscale-update-auto-scaling-group --max-size 0 --min-size 0 --desired-capacity 0 asg-euca-internal-imaging-worker-01
Once the command has been executed, then the Image Worker instance will be terminated.
When this happens however, the cloud administrator must re-launch the Image Worker instance in order to re-enable support for the services provided by the Image Worker instance. To do so, use the euscale-update-auto-scaling-group command to update the group size to 1 or greater (this depends upon how much this service is utilized on a given Eucalpytus 4.0 cloud):
$ euscale-update-auto-scaling-group --max-size 1 --min-size 1 --desired-capacity 1 asg-euca-internal-imaging-worker-01
This will relaunch the Image Worker instance, and re-establish the associated services on the Eucalyptus 4.0 Cloud.