Ensure DNS is looked up on boostrap

PR etcd-io#13224 introduced an early exit when the names match. This change
restores the previous behaviour by doing an explicit DNS resolution
before checking the URLs for equality.

Signed-off-by: Thomas Jungblut <tjungblu@redhat.com>

pkg/netutil/netutil.go

@@ -60,10 +60,10 @@ func resolveTCPAddrDefault(ctx context.Context, addr string) (*net.TCPAddr, erro
 	return &net.TCPAddr{IP: ip.IP, Port: portnum, Zone: ip.Zone}, nil
 }
 
-// resolveTCPAddrs is a convenience wrapper for net.ResolveTCPAddr.
-// resolveTCPAddrs return a new set of url.URLs, in which all DNS hostnames
+// ResolveTCPAddrs is a convenience wrapper for net.ResolveTCPAddr.
+// ResolveTCPAddrs return a new set of url.URLs, in which all DNS hostnames
 // are resolved.
-func resolveTCPAddrs(ctx context.Context, lg *zap.Logger, urls [][]url.URL) ([][]url.URL, error) {
+func ResolveTCPAddrs(ctx context.Context, lg *zap.Logger, urls [][]url.URL) ([][]url.URL, error) {
 	newurls := make([][]url.URL, 0)
 	for _, us := range urls {
 		nus := make([]url.URL, len(us))
@@ -163,7 +163,7 @@ func urlsEqual(ctx context.Context, lg *zap.Logger, a []url.URL, b []url.URL) (b
 	}
 
 	// If URLs are not equal, try to resolve it and compare again.
-	urls, err := resolveTCPAddrs(ctx, lg, [][]url.URL{a, b})
+	urls, err := ResolveTCPAddrs(ctx, lg, [][]url.URL{a, b})
 	if err != nil {
 		return false, err
 	}

pkg/netutil/netutil_test.go

@@ -130,7 +130,7 @@ func TestResolveTCPAddrs(t *testing.T) {
 			return &net.TCPAddr{IP: net.ParseIP(tt.hostMap[host]), Port: i, Zone: ""}, nil
 		}
 		ctx, cancel := context.WithTimeout(context.TODO(), time.Second)
-		urls, err := resolveTCPAddrs(ctx, zap.NewExample(), tt.urls)
+		urls, err := ResolveTCPAddrs(ctx, zap.NewExample(), tt.urls)
 		cancel()
 		if tt.hasError {
 			if err == nil {

server/config/config.go

@@ -17,8 +17,8 @@ package config
 import (
 	"context"
 	"fmt"
+	"net/url"
 	"path/filepath"
-	"sort"
 	"strings"
 	"time"
 
@@ -240,11 +240,17 @@ func (c *ServerConfig) hasLocalMember() error {
 
 // advertiseMatchesCluster confirms peer URLs match those in the cluster peer list.
 func (c *ServerConfig) advertiseMatchesCluster() error {
-	urls, apurls := c.InitialPeerURLsMap[c.Name], c.PeerURLs.StringSlice()
-	urls.Sort()
-	sort.Strings(apurls)
+	urls := c.InitialPeerURLsMap[c.Name]
 	ctx, cancel := context.WithTimeout(context.TODO(), 30*time.Second)
 	defer cancel()
+
+	// try to resolve the urls that were passed to fail early on bootstrap
+	_, err := netutil.ResolveTCPAddrs(ctx, c.Logger, [][]url.URL{urls, c.PeerURLs})
+	if err != nil {
+		return fmt.Errorf("failed to resolve addresses: --initial-cluster=%s --initial-advertise-peer-urls=%s (%v)", urls, c.PeerURLs, err)
+	}
+
+	apurls := c.PeerURLs.StringSlice()
 	ok, err := netutil.URLStringsEqual(ctx, c.Logger, apurls, urls.StringSlice())
 	if ok {
 		return nil