Update more metrics names (#3799)

The subsystem of a metric must be it's plugin name. "dns" is reserved
for the core. Use a const convention to avoid copy-paste mistakes in
naming.

Fix dns64 and acl plugin.

Signed-off-by: Ben Kochie <superq@gmail.com>

plugin/dns64/README.md

@@ -6,8 +6,6 @@
 
 ## Description
 
-From Wikipedia:
-
 > DNS64 describes a DNS server that when asked for a domain's AAAA records, but only finds
 > A records, synthesizes the AAAA records from the A records.
 
@@ -56,6 +54,15 @@ dns64 {
 
 * `prefix` specifies any local IPv6 prefix to use, instead of the well known prefix (64:ff9b::/96)
 
+
+## Metrics
+
+If monitoring is enabled (via the _prometheus_ plugin) then the following metrics are exported:
+
+- `coredns_dns64_requests_translated_total{server}` - counter of DNS requests translated
+
+The `server` label is explained in the _prometheus_ plugin documentation.
+
 ## Bugs
 
 Not all features required by DNS64 are implemented, only basic AAAA synthesis.

plugin/dns64/metrics.go

@@ -10,8 +10,8 @@ var (
 	// RequestsTranslatedCount is the number of DNS requests translated by dns64.
 	RequestsTranslatedCount = prometheus.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
-		Subsystem: "dns",
-		Name:      "requests_dns64_translated_total",
+		Subsystem: pluginName,
+		Name:      "requests_translated_total",
 		Help:      "Counter of DNS requests translated by dns64.",
 	}, []string{"server"})
 )

plugin/dns64/setup.go

@@ -12,14 +12,16 @@ import (
 	"github.com/caddyserver/caddy"
 )
 
-var log = clog.NewWithPlugin("dns64")
+const pluginName = "dns64"
 
-func init() { plugin.Register("dns64", setup) }
+var log = clog.NewWithPlugin(pluginName)
+
+func init() { plugin.Register(pluginName, setup) }
 
 func setup(c *caddy.Controller) error {
 	dns64, err := dns64Parse(c)
 	if err != nil {
-		return plugin.Error("dns64", err)
+		return plugin.Error(pluginName, err)
 	}
 
 	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {