etcdmain: resolve DNS hostnames for client and peer URLs

etcd resolves DNS hostnames to IP addresses for client and peer URLs
before creating any listening sockets.

The following messages are logged during startup:

    etcd: Resolving infra0.coreos.com:2380 to 10.0.1.10:2380

Fixes #1991

etcdmain/config.go

@@ -17,6 +17,7 @@
 package etcdmain
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"log"
@@ -27,6 +28,7 @@ import (
 	"github.com/coreos/etcd/etcdserver"
 	"github.com/coreos/etcd/pkg/cors"
 	"github.com/coreos/etcd/pkg/flags"
+	"github.com/coreos/etcd/pkg/netutil"
 	"github.com/coreos/etcd/pkg/transport"
 	"github.com/coreos/etcd/version"
 )
@@ -242,9 +244,17 @@ func (cfg *config) Parse(arguments []string) error {
 		return err
 	}
 
+	if err := cfg.resolveUrls(); err != nil {
+		return errors.New("cannot resolve DNS hostnames.")
+	}
+
 	return nil
 }
 
+func (cfg *config) resolveUrls() error {
+	return netutil.ResolveTCPAddrs(cfg.lpurls, cfg.apurls, cfg.lcurls, cfg.acurls)
+}
+
 func (cfg config) isNewCluster() bool          { return cfg.clusterState.String() == clusterStateFlagNew }
 func (cfg config) isProxy() bool               { return cfg.proxy.String() != proxyFlagOff }
 func (cfg config) isReadonlyProxy() bool       { return cfg.proxy.String() == proxyFlagReadonly }

pkg/netutil/netutil.go

@@ -0,0 +1,57 @@
+/*
+   Copyright 2014 CoreOS, Inc.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package netutil
+
+import (
+	"log"
+	"net"
+	"net/url"
+)
+
+var (
+	// indirection for testing
+	resolveTCPAddr = net.ResolveTCPAddr
+)
+
+// ResolveTCPAddrs is a convenience wrapper for net.ResolveTCPAddr.
+// ResolveTCPAddrs resolves all DNS hostnames in-place for the given set of
+// url.URLs.
+func ResolveTCPAddrs(urls ...[]url.URL) error {
+	for _, us := range urls {
+		for i, u := range us {
+			host, _, err := net.SplitHostPort(u.Host)
+			if err != nil {
+				log.Printf("netutil: Could not parse url %s during tcp resolving.", u.Host)
+				return err
+			}
+			if host == "localhost" {
+				continue
+			}
+			if net.ParseIP(host) != nil {
+				continue
+			}
+			tcpAddr, err := resolveTCPAddr("tcp", u.Host)
+			if err != nil {
+				log.Printf("netutil: Could not resolve host: %s", u.Host)
+				return err
+			}
+			log.Printf("netutil: Resolving %s to %s", u.Host, tcpAddr.String())
+			us[i].Host = tcpAddr.String()
+		}
+	}
+	return nil
+}

pkg/netutil/netutil_test.go

@@ -0,0 +1,140 @@
+/*
+   Copyright 2014 CoreOS, Inc.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package netutil
+
+import (
+	"errors"
+	"net"
+	"net/url"
+	"reflect"
+	"strconv"
+	"testing"
+)
+
+func TestResolveTCPAddrs(t *testing.T) {
+	defer func() { resolveTCPAddr = net.ResolveTCPAddr }()
+	tests := []struct {
+		urls     [][]url.URL
+		expected [][]url.URL
+		hostMap  map[string]string
+		hasError bool
+	}{
+		{
+			urls: [][]url.URL{
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "127.0.0.1:4001"},
+					url.URL{Scheme: "http", Host: "127.0.0.1:2379"},
+				},
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "127.0.0.1:7001"},
+					url.URL{Scheme: "http", Host: "127.0.0.1:2380"},
+				},
+			},
+			expected: [][]url.URL{
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "127.0.0.1:4001"},
+					url.URL{Scheme: "http", Host: "127.0.0.1:2379"},
+				},
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "127.0.0.1:7001"},
+					url.URL{Scheme: "http", Host: "127.0.0.1:2380"},
+				},
+			},
+		},
+		{
+			urls: [][]url.URL{
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "infra0.example.com:4001"},
+					url.URL{Scheme: "http", Host: "infra0.example.com:2379"},
+				},
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "infra0.example.com:7001"},
+					url.URL{Scheme: "http", Host: "infra0.example.com:2380"},
+				},
+			},
+			expected: [][]url.URL{
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "10.0.1.10:4001"},
+					url.URL{Scheme: "http", Host: "10.0.1.10:2379"},
+				},
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "10.0.1.10:7001"},
+					url.URL{Scheme: "http", Host: "10.0.1.10:2380"},
+				},
+			},
+			hostMap: map[string]string{
+				"infra0.example.com": "10.0.1.10",
+			},
+			hasError: false,
+		},
+		{
+			urls: [][]url.URL{
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "infra0.example.com:4001"},
+					url.URL{Scheme: "http", Host: "infra0.example.com:2379"},
+				},
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "infra0.example.com:7001"},
+					url.URL{Scheme: "http", Host: "infra0.example.com:2380"},
+				},
+			},
+			hostMap: map[string]string{
+				"infra0.example.com": "",
+			},
+			hasError: true,
+		},
+		{
+			urls: [][]url.URL{
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "ssh://infra0.example.com:4001"},
+					url.URL{Scheme: "http", Host: "ssh://infra0.example.com:2379"},
+				},
+				[]url.URL{
+					url.URL{Scheme: "http", Host: "ssh://infra0.example.com:7001"},
+					url.URL{Scheme: "http", Host: "ssh://infra0.example.com:2380"},
+				},
+			},
+			hasError: true,
+		},
+	}
+	for _, tt := range tests {
+		resolveTCPAddr = func(network, addr string) (*net.TCPAddr, error) {
+			host, port, err := net.SplitHostPort(addr)
+			if err != nil {
+				return nil, err
+			}
+			if tt.hostMap[host] == "" {
+				return nil, errors.New("cannot resolve host.")
+			}
+			i, err := strconv.Atoi(port)
+			if err != nil {
+				return nil, err
+			}
+			return &net.TCPAddr{IP: net.ParseIP(tt.hostMap[host]), Port: i, Zone: ""}, nil
+		}
+		err := ResolveTCPAddrs(tt.urls...)
+		if tt.hasError {
+			if err == nil {
+				t.Errorf("expected error")
+			}
+			continue
+		}
+		if !reflect.DeepEqual(tt.urls, tt.expected) {
+			t.Errorf("expected: %v, got %v", tt.expected, tt.urls)
+		}
+	}
+}

test

@@ -15,7 +15,7 @@ COVER=${COVER:-"-cover"}
 source ./build
 
 # Hack: gofmt ./ will recursively check the .git directory. So use *.go for gofmt.
-TESTABLE_AND_FORMATTABLE="client discovery error etcdctl/command etcdmain etcdserver etcdserver/etcdhttp etcdserver/etcdhttp/httptypes etcdserver/etcdserverpb integration migrate pkg/fileutil pkg/flags pkg/ioutils pkg/types pkg/transport pkg/wait proxy raft rafthttp snap store wal"
+TESTABLE_AND_FORMATTABLE="client discovery error etcdctl/command etcdmain etcdserver etcdserver/etcdhttp etcdserver/etcdhttp/httptypes etcdserver/etcdserverpb integration migrate pkg/fileutil pkg/flags pkg/ioutils pkg/netutil pkg/types pkg/transport pkg/wait proxy raft rafthttp snap store wal"
 FORMATTABLE="$TESTABLE_AND_FORMATTABLE *.go etcdctl/"
 
 # user has not provided PKG override