middleware/{log,errors}: output everything to stdout (#684)

Limit the options in both errors and log middleware, just output to
stdout and let someone else (journald,docker) care about where to route
the logs. This removes syslog and logging to a file.

Fixes #573 #602

middleware/log/setup.go

@@ -1,7 +1,7 @@
 package log
 
 import (
-	"io"
+	"fmt"
 	"log"
 	"os"
 
@@ -9,7 +9,6 @@ import (
 	"github.com/coredns/coredns/middleware"
 	"github.com/coredns/coredns/middleware/pkg/response"
 
-	"github.com/hashicorp/go-syslog"
 	"github.com/mholt/caddy"
 	"github.com/miekg/dns"
 )
@@ -30,25 +29,10 @@ func setup(c *caddy.Controller) error {
 	// Open the log files for writing when the server starts
 	c.OnStartup(func() error {
 		for i := 0; i < len(rules); i++ {
-			var err error
-			var writer io.Writer
-
-			if rules[i].OutputFile == "stdout" {
-				writer = os.Stdout
-			} else if rules[i].OutputFile == "stderr" {
-				writer = os.Stderr
-			} else if rules[i].OutputFile == "syslog" {
-				writer, err = gsyslog.NewLogger(gsyslog.LOG_INFO, "LOCAL0", "coredns")
-				if err != nil {
-					return middleware.Error("log", err)
-				}
-			} else {
-				var file *os.File
-				file, err = os.OpenFile(rules[i].OutputFile, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0644)
-				if err != nil {
-					return middleware.Error("log", err)
-				}
-				writer = file
+			// We only support stdout
+			writer := os.Stdout
+			if rules[i].OutputFile != "stdout" {
+				return middleware.Error("log", fmt.Errorf("invalid log file: %s", rules[i].OutputFile))
 			}
 
 			rules[i].Log = log.New(writer, "", 0)
@@ -78,7 +62,7 @@ func logParse(c *caddy.Controller) ([]Rule, error) {
 				Format:     DefaultLogFormat,
 			})
 		} else if len(args) == 1 {
-			// Only an output file specified
+			// Only an output file specified.
 			rules = append(rules, Rule{
 				NameScope:  ".",
 				OutputFile: args[0],