Allocation policy

An allocation policy decides on which host each task runs, and when. The type selects the kind of policy:

Type	Description
prefab	A ready-made policy, selected by name. See prefabs.
filter	A policy built from filters and weighers.
timeshift	A filter policy that also delays tasks while the carbon intensity is high. See time-shifting.

Filter policies

A filter policy places each task in two steps:

1. The filters remove the hosts that cannot run the task.
2. The weighers rank the remaining hosts. Each weigher's score is weighted by its multiplier. A negative multiplier prefers low values instead of high ones.

The task goes to the best host, or to a random host among the subsetSize best hosts.

Field	Type	Default	Description
filters	list of filters	[{ "type": "Compute" }]	The filters, all of which a host must pass.
weighers	list of weighers	[]	The weighers that rank the hosts.
subsetSize	integer	1	The number of best hosts from which one is picked at random.

{
    "type": "filter",
    "filters": [
        { "type": "Compute" },
        { "type": "VCpu", "allocationRatio": 1.0 },
        { "type": "Ram" }
    ],
    "weighers": [
        { "type": "Ram", "multiplier": 1.0 }
    ]
}

Filters

Type	Fields	Keeps the hosts that
Compute		are up.
VCpu	allocationRatio (default 1.0)	have enough free CPU cores. An allocationRatio above 1 allows overcommitting cores.
VCpuCapacity		have cores at least as fast as the task needs.
Ram	allocationRatio (default 1.0)	have enough free memory. Do not change allocationRatio: overcommitting memory is not supported.
InstanceCount	limit	run fewer than limit tasks.
SameHost		Currently has no effect.
DifferentHost		Currently has no effect.

Weighers

Every weigher has a multiplier (default 1.0).

Type	Scores a host by
Ram	its free memory.
CoreRam	its free memory per core.
InstanceCount	the number of tasks it runs.
VCpuCapacity	its CPU capacity.
VCpu	how few CPU cores are provisioned on it. A higher score means fewer cores in use.

Time-shifting

A timeshift policy filters and weighs hosts like a filter policy, but also delays deferrable tasks while the carbon intensity is high, as long as they can still meet their deadline. Tasks shorter than two hours use shortForecastThreshold, longer tasks use longForecastThreshold. The carbon intensity comes from the carbon trace of the power source.

Field	Type	Default	Description
filters	list of filters	[{ "type": "Compute" }]	The filters, all of which a host must pass.
weighers	list of weighers	[]	The weighers that rank the hosts.
subsetSize	integer	1	The number of best hosts from which one is picked at random.
forecast	boolean	true	Compare the carbon intensity with a forecast. Otherwise, compare it with the mean of the last windowSize values.
forecastSize	integer	24	The number of forecasted values to compare with.
shortForecastThreshold	number	0.2	The carbon intensity is low for short tasks when it is below this quantile of the forecast.
longForecastThreshold	number	0.35	The same, for long tasks.
windowSize	integer	168	The number of past values in the mean.
memorize	boolean	true	Use the faster memorizing scheduler, which places each task on a fitting host with the fewest tasks and ignores the weighers.
taskStopper	task stopper	none	Also pauses running tasks while the carbon intensity is high.

Task stopper

Field	Type	Default	Description
forecast	boolean	true	Use a forecast instead of past values.
forecastSize	integer	24	The number of forecasted values.
forecastThreshold	number	0.6	The threshold, between 0 and 1, above which tasks are paused.
windowSize	integer	168	The number of past values used.

{
    "type": "timeshift",
    "filters": [{ "type": "Compute" }, { "type": "VCpu" }, { "type": "Ram" }],
    "weighers": [{ "type": "Ram" }],
    "shortForecastThreshold": 0.2,
    "longForecastThreshold": 0.35,
    "taskStopper": { "forecastThreshold": 0.6 }
}

Prefabs

A prefab is a ready-made policy, selected by name. The name is not case-sensitive.

{ "type": "prefab", "policyName": "Mem" }

Unless noted otherwise, the prefabs use the Compute, VCpu and Ram filters. The GPU prefabs also check that a host has enough free GPU cores.

Prefab	Weighers	Notes
Mem	Ram (1.0)	The default policy. Uses only the VCpu and Ram filters.
MemInv	Ram (-1.0)
CoreMem	CoreRam (1.0)
CoreMemInv	CoreRam (-1.0)
ActiveServers	InstanceCount (-1.0)
ActiveServersInv	InstanceCount (1.0)
ProvisionedCores	VCpu (1.0)
ProvisionedCoresInv	VCpu (-1.0)
Random	none	Picks a random host that passes the filters.
TaskNumMemorizing	none	Places each task on a fitting host with the fewest tasks.
Timeshift	Ram (1.0)	With time-shifting, using its defaults.
ProvisionedCpuGpuCores	VCpu (1.0), GPU cores (1.0)	GPU prefab.
ProvisionedCpuGpuCoresInv	VCpu (-1.0), GPU cores (-1.0)	GPU prefab.
GpuTaskMemorizing	none	GPU prefab. Places each task on a fitting host with the fewest tasks.