On 09/01/2017 04:42 AM, Rua, Philippe (Nokia - FI/Espoo) wrote:
Will it be possible to include network bandwidth as a resource in Nova
scheduling, for VM placement decision?
Yes.
See here for a related Neutron spec that mentions Placement:
https://review.openstack.org/#/c/396297/7/specs/pike/strict-minimum-bandwidth-support.rst
Context: in telecommunication applications, the network traffic is an important dimension
of resource usage. For example, it is often important to distribute
"bandwidth-greedy" VMs to different compute nodes. There were some earlier
discussions on this topic, but I could not find a concrete outcome. [1][2][3]
After some reading, I wonder whether the Custom resource classes can provide a
generic mechanism? [4][5][6]
No :) Custom resource classes are antithetical to generic/standard
mechanisms.
We want to add two *standard* resource classes, one called
NET_INGRESS_BYTES_SEC and another called NET_EGRESS_BYTES_SEC which
would represent the total bandwidth in bytes per second the for
corresponding traffic directions.
What would be the resource provider, though? There are at least two
potential answers here:
1) A network interface controller on the compute host
In this case, the NIC on the host would be a child provider of the
compute host resource provider. It would have an inventory record of
resource class NET_INGRESS_BYTES_SEC with a total value representing the
entire bandwidth of the host NIC. Instances would consume some amount of
NET_INGRESS_BYTES_SEC corresponding to *either* the Nova flavor (if the
resources:NET_INGRESS_BYTES_SEC extra-spec is set) *or* to the sum of
consumed bandwidth amounts from the port profile of any ports specified
when launching the instance (and thus would be part of the pci device
request collection attached to the build request).
2) A "network slice" of a network interface controller on the compute host
In this case, assume that the NIC on the compute host has had its total
bandwidth constrained via traffic control so that 50% of its available
ingress bandwidth is allocated to network A and 50% is allocated to
network B.
There would be multiple resources providers, each with an inventory
record of resource class NET_INGRESS_BYTES_SEC with a total value of 1/2
the total NIC bandwidth. Both of these resource providers would be child
providers of the compute host resource provider. One of these child
resource providers will be decorated with the trait "CUSTOM_NETWORK_A"
and the other with trait "CUSTOM_NETWORK_B".
The scheduler would be able to determine which resource provider to
consume the NET_INGRESS_BYTES_SEC resources from by looking for a
resource provider that has both the required amount of
NET_INGRESS_BYTES_SEC as well as the trait required by the port profile.
If, say, the port profile specifies that the port is to go on a NIC with
access to network "A", then the build request would contain a request to
the scheduler for CUSTOM_NETWORK_A trait...
If you're coming to Denver, I encourage you to get with me, Sean Mooney,
Moshe Levi and others who are interested in seeing this work move forward.
Best,
-jay
Here is what I have in mind:
- The VM need is specified in the flavor extra-specs, e.g.
resources:CUSTOM_BANDWIDTH=123.
- The compute node total capacity is specified in host aggregate metadata, e.g.
CUSTOM_BANDWIDTH=999.
- Nova then takes care of the rest: scheduling where the free capacity is
sufficient, and performing simple resource usage accounting (updating the
compute node free network bandwidth capacity as required).
Is the outline above according to current plans?
If not, what would be possible/needed in order to achieve the same result, i.e.
consider the VM network traffic need during VM placement?
BR,
Philippe
[1] https://blueprints.launchpad.net/nova/+spec/bandwidth-as-scheduler-metric
[2] https://wiki.openstack.org/wiki/NetworkBandwidthEntitlement
[3]
https://openstack.nimeyo.com/80515/openstack-scheduling-bandwidth-resources-nic_bw_kb-resource
[4] https://docs.openstack.org/nova/latest/user/placement.html
[5]
http://specs.openstack.org/openstack/nova-specs/priorities/pike-priorities.html#placement
[6] https://review.openstack.org/#/c/473627/
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