Target Plugins

Target plugins are used by the autoscaler to retrieve information about a scaling target and also to perform a scaling action against them.

For a real-world example of a Nomad Target plugin implementation, see the Nomad group->count plugin.

Authoring Target Plugins

Authoring a target plugin in Go can be accomplished by implementing the target.Target interface, alongside a main package to launch the plugin.

The no-op Target plugin can be used as a starting point for new Target plugins.

Target Plugin API

The base plugin interface must be implemented in addition to the following functions.

Scale(action sdk.ScalingAction, config map[string]string) error

The Scale method is called by the agent during policy evaluation. The action argument specifies the details about the scaling action that should be made against the target. config includes the details about the scaling target that were provided in the scaling policy.

Status(config map[string]string) (*sdk.TargetStatus, error)

The Status method is called by the agent in order to determine the current status of a scaling target. This is performed as part of policy evaluation, and the information returned may be used by the scaling strategy to inform the next scaling action. Information returned includes current scaling level, readiness, and arbitrary metadata.