func NewContextualInstancer(i sd.Instancer, m map[string]interface{}) sd.Instancer {
	if len(m) == 0 {
		return i
	}
	return ContextualInstancer{i, m}
}
NewContextualInstancer returns an sd.Instancer that has been enriched with metadata.
This metadata allows infrastructure to carry configuration information about the instancer
across API boundaries so that it can be logged or otherwise processed.

If m is empty, i is returned as is.
package service
import (
	"github.com/go-kit/kit/sd"
)
type ContextualInstancer struct {
	sd.Instancer
	m map[string]interface{}
}
func (ci ContextualInstancer) Metadata() map[string]interface{} {
	return ci.m
}