pass-through strategy plugin

plugins/builtin/strategy/pass-thru/main.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	hclog "github.com/hashicorp/go-hclog"
+	"github.com/hashicorp/nomad-autoscaler/plugins"
+	passthru "github.com/hashicorp/nomad-autoscaler/plugins/builtin/strategy/pass-thru/plugin"
+)
+
+func main() {
+	plugins.Serve(factory)
+}
+
+// factory returns a new instance of the PassThru Strategy plugin.
+func factory(log hclog.Logger) interface{} {
+	return passthru.NewPassThruPlugin(log)
+}

plugins/builtin/strategy/pass-thru/plugin/plugin.go

@@ -0,0 +1,97 @@
+package plugin
+
+import (
+	"fmt"
+
+	"github.com/hashicorp/go-hclog"
+	"github.com/hashicorp/nomad-autoscaler/plugins"
+	"github.com/hashicorp/nomad-autoscaler/plugins/base"
+	"github.com/hashicorp/nomad-autoscaler/plugins/strategy"
+	"github.com/hashicorp/nomad-autoscaler/sdk"
+)
+
+const (
+	// pluginName is the unique name of the this plugin amongst strategy
+	// plugins.
+	pluginName = "pass-thru"
+)
+
+var (
+	PluginID = plugins.PluginID{
+		Name:       pluginName,
+		PluginType: sdk.PluginTypeStrategy,
+	}
+
+	PluginConfig = &plugins.InternalPluginConfig{
+		Factory: func(l hclog.Logger) interface{} { return NewPassThruPlugin(l) },
+	}
+
+	pluginInfo = &base.PluginInfo{
+		Name:       pluginName,
+		PluginType: sdk.PluginTypeStrategy,
+	}
+)
+
+// Assert that StrategyPlugin meets the strategy.Strategy interface.
+var _ strategy.Strategy = (*StrategyPlugin)(nil)
+
+// StrategyPlugin is the None implementation of the strategy.Strategy
+// interface.
+type StrategyPlugin struct {
+	logger hclog.Logger
+}
+
+// NewTargetValuePlugin returns the None implementation of the
+// strategy.Strategy interface.
+func NewPassThruPlugin(log hclog.Logger) strategy.Strategy {
+	return &StrategyPlugin{
+		logger: log,
+	}
+}
+
+// SetConfig satisfies the SetConfig function on the base.Base interface.
+func (s *StrategyPlugin) SetConfig(config map[string]string) error {
+	return nil
+}
+
+// PluginInfo satisfies the PluginInfo function on the base.Base interface.
+func (s *StrategyPlugin) PluginInfo() (*base.PluginInfo, error) {
+	return pluginInfo, nil
+}
+
+// Run satisfies the Run function on the strategy.Strategy interface.
+func (s *StrategyPlugin) Run(eval *sdk.ScalingCheckEvaluation, count int64) (*sdk.ScalingCheckEvaluation, error) {
+
+	// Use only the latest value for now.
+	metric := eval.Metrics[len(eval.Metrics)-1]
+
+
+	// TODO: compare count > metric --> direction
+	// Identify the direction of scaling, if any.
+	eval.Action.Direction = s.calculateDirection(count, metric.Value)
+	if eval.Action.Direction == sdk.ScaleDirectionNone {
+		return eval, nil
+	}
+
+
+	eval.Action.Count = int64(metric.Value)
+	eval.Action.Reason = fmt.Sprintf("scaling %s because metric is %d", eval.Action.Direction, eval.Action.Count)
+
+	return eval, nil
+}
+
+// calculateDirection is used to calculate the direction of scaling that should
+// occur, if any at all. It takes into account the current task group count in
+// order to correctly account for 0 counts.
+//
+// The input factor value is padded by e, such that no action will be taken if
+// factor is within [1-e; 1+e].
+func (s *StrategyPlugin) calculateDirection(count int64, metric float64) sdk.ScaleDirection {
+	if metric > float64(count) {
+		return sdk.ScaleDirectionUp
+	} else if metric < float64(count) {
+		return sdk.ScaleDirectionDown
+	} else {
+		return sdk.ScaleDirectionNone
+	}
+}