The instance size is determined by its flavor, not the image. In case the image is too large for the chosen flavor, the instance doesn't launch and ends up in state ERROR.

Hi @najeh, issues like this are normally related to the size of the image being too big for the flavor you are using (set of ram vcpu and disk size) as mentioned by @Bernd .

Normally for public clouds, a set of flavors are provided to customer allow them to create their own VMs with them and you provide a set of image that are no grether than the actual size of the disk. All this having in mind that the image are raw images and not compressed images as (qcow, qcow2 and some VHD or VHDX ).

Or for private clouds were you choose your own set of flavor and create them for each of the VMs configurations you require.

From here, you have some options.

1. Set private flavors for the project you require to create the new image based on this snapshot.
2. Create volumes with the size you require, then create the VM based on the volume instead of an image.

openstack volume create --image image-id --type Type-ID --size Size greater than the actual image name

openstack server create --flavor ID --volume VolumeID --key-name KeyName --nic net-id=NetID Name