diff --git a/internal/net/tcp/dialer.go b/internal/net/tcp/dialer.go
index 150e84b490..3e87143b12 100644
--- a/internal/net/tcp/dialer.go
+++ b/internal/net/tcp/dialer.go
@@ -20,6 +20,7 @@ package tcp
 import (
 	"context"
 	"crypto/tls"
+	"errors"
 	"strings"
 	"time"
 
@@ -29,6 +30,7 @@ import (
 	"github.com/vdaas/vald/internal/safety"
 )
 
+// Dialer is an interface to get the dialer instance to connect to an address.
 type Dialer interface {
 	GetDialer() func(ctx context.Context, network, addr string) (net.Conn, error)
 	StartDialerCache(ctx context.Context)
@@ -56,6 +58,10 @@ func NewDialer(opts ...DialerOption) (der Dialer, err error) {
 		opt(d)
 	}
 
+	if d.dnsRefreshDuration > d.dnsCacheExpiration {
+		return nil, errors.New("dnsRefreshDuration > dnsCacheExpiration")
+	}
+
 	d.der = &net.Dialer{
 		Timeout:   d.dialerTimeout,
 		KeepAlive: d.dialerKeepAlive,
@@ -83,13 +89,6 @@ func NewDialer(opts ...DialerOption) (der Dialer, err error) {
 		return d, nil
 	}
 
-	if d.dnsRefreshDuration > d.dnsCacheExpiration {
-		d.dnsRefreshDuration, d.dnsCacheExpiration =
-			d.dnsCacheExpiration, d.dnsRefreshDuration
-		d.dnsRefreshDurationStr, d.dnsCacheExpirationStr =
-			d.dnsCacheExpirationStr, d.dnsRefreshDurationStr
-	}
-
 	if d.cache == nil {
 		d.cache, err = cache.New(
 			cache.WithExpireDuration(d.dnsCacheExpirationStr),
@@ -118,16 +117,14 @@ func NewDialer(opts ...DialerOption) (der Dialer, err error) {
 	return d, nil
 }
 
-func (d *dialer) GetDialer() func(ctx context.Context,
-	network, addr string) (net.Conn, error) {
+func (d *dialer) GetDialer() func(ctx context.Context, network, addr string) (net.Conn, error) {
 	return d.dialer
 }
 
-func (d *dialer) lookup(ctx context.Context,
-	addr string) (ips map[int]string, err error) {
+func (d *dialer) lookup(ctx context.Context, addr string) (ips []string, err error) {
 	cache, ok := d.cache.Get(addr)
 	if ok {
-		return cache.(map[int]string), nil
+		return cache.([]string), nil
 	}
 
 	r, err := d.der.Resolver.LookupIPAddr(ctx, addr)
@@ -135,9 +132,9 @@ func (d *dialer) lookup(ctx context.Context,
 		return nil, err
 	}
 
-	ips = make(map[int]string, len(r))
-	for i, ip := range r {
-		ips[i] = ip.String()
+	ips = make([]string, 0, len(r)+2)
+	for _, ip := range r {
+		ips = append(ips, ip.String())
 	}
 
 	d.cache.Set(addr, ips)