[Core] Assign a fractional CPU to the Ray node

[John-Almardeny]

What happened + What you expected to happen

I tried to assign a fractional CPU to the Ray Worker Node, yet it threw the following error:

error invalid value for '--num cpus': 0.5 is not a valid integer ray

It is clear that --num cpus does not accept a float, but in our case, assigning a fractional CPU to the Ray node is crucial.

Versions / Dependencies

ray[default]==2.2.0

Reproduction script

In the K8s YAML file : Deployment of Worker Nodes

We pass the following command to start Ray worker node:

args:
     - "ray start --num-cpus=0.5 --redis-password=5241590000000000 ....."

Issue Severity

High: It blocks me from completing my task.

[John-Almardeny]

Hi lads @rkooo567, @edoakes ,

Can you please have a look at this? Much appreciated!

[rkooo567]

I think we can support it just for CPU (but it makes no sense for GPU). Can you tell us a little more detail about the use case? Also, feel free to contribute it!

[John-Almardeny]

The use-case is we have an actor that should live in one K8s Pod / Ray Worker Node alone, and due to resource constraints and because it suffices for us, we need to allocate a fractional CPU < 1 to it.