topolvm-scheduler.md

topolvm-scheduler

topolvm-scheduler is a Kubernetes scheduler extender for TopoLVM.

It filters and prioritizes Nodes based on the amount of free space in their volume groups.

Scheduler policy

topolvm-scheduler need to be configured in scheduler policy as follows:

{
    ...
    "extenders": [{
        "urlPrefix": "http://...",
        "filterVerb": "predicate",
        "prioritizeVerb": "prioritize",
        "managedResources":
        [{
          "name": "topolvm.cybozu.com/capacity",
          "ignoredByScheduler": true
        }],
        "nodeCacheCapable": false
    }]
}

As shown, only pods that request topolvm.cybozu.com/capacity resource are managed by topolvm-scheduler.

Verbs

The extender provides two verbs:

• predicate to filter nodes
• prioritize to score nodes

predicate

This verb filters out nodes whose volume groups have not enough free space.

Volume group capacity is identified from the value of capacity.topolvm.cybozu.com/<device-class> annotation.

prioritize

This verb scores nodes. The score of a node is calculated by this formula:

min(10, max(0, log2(capacity >> 30 / divisor)))

divisor can be given through the configuration file.

Command-line flags

Name	Type	Default	Description
config	string	``	Config file path

Config file format

The divisor parameter can be specified in YAML file:

default-divisor: 10
divisors:
  ssd: 5
  hdd: 10

Name	Type	Default	Description
listen	string	:8000	HTTP listening address
default-divisor	float64	1	A default value of the variable for node scoring.
divisors	map[string]float64	{}	A variable for node scoring per device-class.