Instead of hardcoding plugin lists in autopath/health, use interfaces. (#1306)

Switched health and autopath plugin to allow any plugins to be used instead
of a hardcoded list. I did not switch federation over since it wasn't
obvious that anything other than kubernetes could be used with it.

Fixes #1291

plugin/health/README.md

@@ -18,10 +18,7 @@ supports health checks has a section "Health" in their README.
 
 ## Plugins
 
-The following plugins report health to the health plugin:
-
-* erratic
-* kubernetes
+Any plugin that implements the Healther interface will be used to report health.
 
 ## Examples
 

plugin/health/healther.go

@@ -36,9 +36,3 @@ func (h *health) poll() {
 	}
 	h.SetOk(true)
 }
-
-// Plugins that implements the Healther interface.
-var healthers = map[string]bool{
-	"erratic":    true,
-	"kubernetes": true,
-}

plugin/health/setup.go

@@ -26,9 +26,9 @@ func setup(c *caddy.Controller) error {
 	h := &health{Addr: addr}
 
 	c.OnStartup(func() error {
-		for he := range healthers {
-			m := dnsserver.GetConfig(c).Handler(he)
-			if x, ok := m.(Healther); ok {
+		plugins := dnsserver.GetConfig(c).Handlers()
+		for _, p := range plugins {
+			if x, ok := p.(Healther); ok {
 				h.h = append(h.h, x)
 			}
 		}