[nova][dev] Improved scheduling error messages

Brito, Hugo Nicodemos Hugo.Brito at windriver.com
Wed Aug 25 13:49:47 UTC 2021


In a prototype, we have improved Nova's scheduling error messages.
This helps both developers and end users better understand the
scheduler problems that occur on creation of an instance.

When a scheduler error happens during instance creation via the nova
upstream, we get the following message on the Overview tab
(Horizon dashboard): "No valid host was found." This doesn't give us
enough information about what really happened, so our solution was to
add more details on the instance's overview page, e.g.:

**Fault:Message** attribute provides a summary of why each host can not
satisfy the instance’s resource requirements, e.g. for controller-0, it
indicates “No valid host was found. Not enough host cell CPUs to fit
instance cell” (where cell is a numa-node or socket).

**Fault:Details** attribute provides even more detail for each
individual host, for example it shows that the instance “required” 2
CPU cores and shows the “actual” CPU cores available on each “numa”
node: “actual:0, numa:1” and “actual:1, numa:0”.

These details are also present using the OpenStack CLI, in the
_fault_ attribute:

- openstack server show <instance>

With that in mind, we'd like to know if you are open to consider such
a change. We are willing to submit a spec and upstream that

- nicodemos
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