plugin/forward: fix healthchecker crash (#2165)

plugin/forward/forward.go

@@ -12,12 +12,15 @@ import (
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/debug"
+	clog "github.com/coredns/coredns/plugin/pkg/log"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
 	ot "github.com/opentracing/opentracing-go"
 )
 
+var log = clog.NewWithPlugin("forward")
+
 // Forward represents a plugin instance that can proxy requests to another (DNS) server. It has a list
 // of proxies each representing one upstream proxy.
 type Forward struct {

plugin/forward/health.go

@@ -31,6 +31,7 @@ func NewHealthChecker(trans string) HealthChecker {
 		return &dnsHc{c: c}
 	}
 
+	log.Warningf("No healthchecker for transport %q", trans)
 	return nil
 }
 

plugin/forward/proxy.go

@@ -50,6 +50,11 @@ func (p *Proxy) SetExpire(expire time.Duration) { p.transport.SetExpire(expire)
 
 // Healthcheck kicks of a round of health checks for this proxy.
 func (p *Proxy) Healthcheck() {
+	if p.health == nil {
+		log.Warning("No healthchecker")
+		return
+	}
+
 	p.probe.Do(func() error {
 		return p.health.Check(p)
 	})