Changing compute offering / scaling VM and root disk

[vonlo123]

We are having problems implementing our idea regarding the compute offerings.

We want to use offerings with a fixed amount of CPU, RAM and local storage so that the KVM host is utilized in the best possible way.
E.g. an offering 1:
1 CPU, 2 GB RAM, 20 GB local storage
Offering 2:
2 CPU 4 GB RAM, 40 GB local storage
etc.

We want to avoid a situation where a few VMs with little CPU/RAM consume the entire storage of the host so that the storage is fully booked but the CPU and RAM are not utilized. That would be a waste of resources.

Of course, we also want to offer the customer the option of changing the compute offering if they need more resources for their VM.
According to the documentation it should be possible.

But after some testing, we have now come to the conclusion that changing an offering/scaling a VM is only possible if Disk offering strictness is set to false in the initial (and target) compute offering of the VM.
But this would allow the user to freely adjust the size of the disk.

Is there a solution to this? Did we miss anything?
How do you ensure that all resources of a nodes are fully utilized?

Version 4.18.1.0 with KVM

[DaanHoogland]

@vonlo123 , did you investigate restricting the API for adjusting the diskoffering?
I expect you would want to disallow the use of https://cloudstack.apache.org/api/apidocs-4.18/apis/updateDiskOffering.html

I am not sure what you have configured in terms of roles, but expect you can work with those.

[weizhouapache]

@vonlo123
there is a global setting allow.diskoffering.change.during.scale.vm
you can change the value to true and retry

[vonlo123]

Hello @weizhouapache
we have changed the setting to true but the problem still remains. We can only choose a different compute offering when disk offering strictness is set to false

[vonlo123]

We solved this issue by denying updateDIskOffering
disk offering strictness needs to be set to false

But this only works when the root disk in the compute offering has the Provisioning type fat. With thin provisioning I still can resize the disk.
It looks like a bug...

[DaanHoogland]

Do you mean that the the user can still call updateDiskOffering despite it being denied in their role?
With thin provisioning the initial size should be just what is really used and it should auto grow up to it's limit.
Please describe the scenario you feel is symptomatic of a bug?

[NuxRo]

@DaanHoogland perhaps resizeVolume is the culprit here.