diff --git a/internal/proxy/proxy.go b/internal/proxy/proxy.go
index fd5a68fbc..89c471910 100644
--- a/internal/proxy/proxy.go
+++ b/internal/proxy/proxy.go
@@ -747,6 +747,14 @@ type socketMount struct {
 	dialOpts []cloudsqlconn.DialOption
 }
 
+func networkType(conf *Config, inst InstanceConnConfig) string {
+	if (conf.UnixSocket == "" && inst.UnixSocket == "" && inst.UnixSocketPath == "") ||
+		(inst.Addr != "" || inst.Port != 0) {
+		return "tcp"
+	}
+	return "unix"
+}
+
 func (c *Client) newSocketMount(ctx context.Context, conf *Config, pc *portConfig, inst InstanceConnConfig) (*socketMount, error) {
 	var (
 		// network is one of "tcp" or "unix"
@@ -765,8 +773,7 @@ func (c *Client) newSocketMount(ctx context.Context, conf *Config, pc *portConfi
 	//   instance)
 	// use a TCP listener.
 	// Otherwise, use a Unix socket.
-	if (conf.UnixSocket == "" && inst.UnixSocket == "" && inst.UnixSocketPath == "") ||
-		(inst.Addr != "" || inst.Port != 0) {
+	if networkType(conf, inst) == "tcp" {
 		network = "tcp"
 
 		a := conf.Addr
@@ -782,8 +789,9 @@ func (c *Client) newSocketMount(ctx context.Context, conf *Config, pc *portConfi
 			np = pc.nextPort()
 		default:
 			version, err := c.dialer.EngineVersion(ctx, inst.Name)
+			// Exit if the port is not specified for inactive instance
 			if err != nil {
-				c.logger.Errorf("could not resolve version for %q: %v", inst.Name, err)
+				c.logger.Errorf("[%v] could not resolve instance version: %v", inst.Name, err)
 				return nil, err
 			}
 			np = pc.nextDBPort(version)
@@ -795,12 +803,13 @@ func (c *Client) newSocketMount(ctx context.Context, conf *Config, pc *portConfi
 
 		version, err := c.dialer.EngineVersion(ctx, inst.Name)
 		if err != nil {
-			c.logger.Errorf("could not resolve version for %q: %v", inst.Name, err)
+			c.logger.Errorf("[%v] could not resolve instance version: %v", inst.Name, err)
 			return nil, err
 		}
 
 		address, err = newUnixSocketMount(inst, conf.UnixSocket, strings.HasPrefix(version, "POSTGRES"))
 		if err != nil {
+			c.logger.Errorf("[%v] could not mount unix socket %q: %v", inst.Name, conf.UnixSocket, err)
 			return nil, err
 		}
 	}
@@ -808,6 +817,7 @@ func (c *Client) newSocketMount(ctx context.Context, conf *Config, pc *portConfi
 	lc := net.ListenConfig{KeepAlive: 30 * time.Second}
 	ln, err := lc.Listen(ctx, network, address)
 	if err != nil {
+		c.logger.Errorf("[%v] could not listen to address %v: %v", inst.Name, address, err)
 		return nil, err
 	}
 	// Change file permissions to allow access for user, group, and other.
diff --git a/internal/proxy/proxy_test.go b/internal/proxy/proxy_test.go
index 8d509295e..807a27264 100644
--- a/internal/proxy/proxy_test.go
+++ b/internal/proxy/proxy_test.go
@@ -17,6 +17,7 @@ package proxy_test
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"net"
 	"os"
@@ -83,6 +84,8 @@ func (f *fakeDialer) EngineVersion(_ context.Context, inst string) (string, erro
 		return "MYSQL_8_0", nil
 	case strings.Contains(inst, "sqlserver"):
 		return "SQLSERVER_2019_STANDARD", nil
+	case strings.Contains(inst, "fakeserver"):
+		return "", fmt.Errorf("non existing server")
 	default:
 		return "POSTGRES_14", nil
 	}
@@ -306,6 +309,17 @@ func TestClientInitialization(t *testing.T) {
 				filepath.Join(testUnixSocketPathPg),
 			},
 		},
+		{
+			desc: "with TCP port for non functional instance",
+			in: &proxy.Config{
+				Instances: []proxy.InstanceConnConfig{
+					{Name: "proj:region:fakeserver", Port: 50000},
+				},
+			},
+			wantTCPAddrs: []string{
+				"127.0.0.1:50000",
+			},
+		},
 	}
 
 	for _, tc := range tcs {
@@ -711,3 +725,86 @@ func TestRunConnectionCheck(t *testing.T) {
 	}
 
 }
+
+func TestProxyInitializationWithFailedUnixSocket(t *testing.T) {
+	ctx := context.Background()
+	testDir, _ := createTempDir(t)
+	testUnixSocketPath := path.Join(testDir, "db")
+
+	tcs := []struct {
+		desc string
+		in   *proxy.Config
+	}{
+		{
+			desc: "with unix socket for non functional instance",
+			in: &proxy.Config{
+				Instances: []proxy.InstanceConnConfig{
+					{
+						Name:           "proj:region:fakeserver",
+						UnixSocketPath: testUnixSocketPath,
+					},
+				},
+			},
+		},
+		{
+			desc: "without TCP port or unix socket for non functional instance",
+			in: &proxy.Config{
+				Instances: []proxy.InstanceConnConfig{
+					{Name: "proj:region:fakeserver"},
+				},
+			},
+		},
+	}
+	for _, tc := range tcs {
+		t.Run(tc.desc, func(t *testing.T) {
+			_, err := proxy.NewClient(ctx, &fakeDialer{}, testLogger, tc.in)
+			if err == nil {
+				t.Fatalf("want non nil error, got = %v", err)
+			}
+		})
+	}
+}
+
+func TestProxyMultiInstances(t *testing.T) {
+	ctx := context.Background()
+	testDir, _ := createTempDir(t)
+	testUnixSocketPath := path.Join(testDir, "db")
+
+	tcs := []struct {
+		desc        string
+		in          *proxy.Config
+		wantSuccess bool
+	}{
+		{
+			desc: "with tcp socket and unix for non functional instance",
+			in: &proxy.Config{
+				Instances: []proxy.InstanceConnConfig{
+					{
+						Name:           "proj:region:fakeserver",
+						UnixSocketPath: testUnixSocketPath,
+					},
+					{Name: mysql, Port: 3306},
+				},
+			},
+			wantSuccess: false,
+		},
+		{
+			desc: "with two tcp socket instances and conflicting ports",
+			in: &proxy.Config{
+				Instances: []proxy.InstanceConnConfig{
+					{Name: "proj:region:fakeserver", Port: 60000},
+					{Name: mysql, Port: 60000},
+				},
+			},
+			wantSuccess: false,
+		},
+	}
+	for _, tc := range tcs {
+		t.Run(tc.desc, func(t *testing.T) {
+			_, err := proxy.NewClient(ctx, &fakeDialer{}, testLogger, tc.in)
+			if tc.wantSuccess != (err == nil) {
+				t.Fatalf("want return = %v, got = %v", tc.wantSuccess, err == nil)
+			}
+		})
+	}
+}