fix: let proxy continue to run with inactive instance(s) (#1854)

Replaced fmt.Errorf with logger.Errorf for instance failure

Fail the inactive instance with unix path

Fixed lint error

Added inactive instance test with unix path

Replace getNetworkType with networkType

internal/proxy/proxy.go

@@ -510,20 +510,20 @@ func NewClient(ctx context.Context, d cloudsql.Dialer, l cloudsql.Logger, conf *
 	for _, inst := range conf.Instances {
 		m, err := c.newSocketMount(ctx, conf, pc, inst)
 		if err != nil {
-			for _, m := range mnts {
-				mErr := m.Close()
-				if mErr != nil {
-					l.Errorf("failed to close mount: %v", mErr)
-				}
+			c.logger.Errorf("[%v] Unable to mount socket: %v", inst.Name, err)
+			if networkType(conf, inst) == "unix" {
+				continue
 			}
-			return nil, fmt.Errorf("[%v] Unable to mount socket: %v", inst.Name, err)
 		}
 
 		l.Infof("[%s] Listening on %s", inst.Name, m.Addr())
 		mnts = append(mnts, m)
 	}
 	c.mnts = mnts
-	return c, nil
+	if len(mnts) > 0 {
+		return c, nil
+	}
+	return nil, fmt.Errorf("No active instance to mount")
 }
 
 // CheckConnections dials each registered instance and reports the number of
@@ -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
@@ -784,7 +791,6 @@ 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)
-				return nil, err
 			}
 			np = pc.nextDBPort(version)
 		}
@@ -801,6 +807,8 @@ func (c *Client) newSocketMount(ctx context.Context, conf *Config, pc *portConfi
 
 		address, err = newUnixSocketMount(inst, conf.UnixSocket, strings.HasPrefix(version, "POSTGRES"))
 		if err != nil {
+			c.logger.Errorf("could not mount unix socket %q for %q: %v",
+				conf.UnixSocket, inst.Name, err)
 			return nil, err
 		}
 	}

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 +309,42 @@ func TestClientInitialization(t *testing.T) {
 				filepath.Join(testUnixSocketPathPg),
 			},
 		},
+		{
+			desc: "without TCP port or unix socket for non functional instance",
+			in: &proxy.Config{
+				Instances: []proxy.InstanceConnConfig{
+					{Name: "proj:region:fakeserver"},
+				},
+			},
+		},
+		{
+			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",
+			},
+		},
+	}
+
+	unixTcs := []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,
+					},
+				},
+			},
+		},
 	}
 
 	for _, tc := range tcs {
@@ -344,6 +383,15 @@ func TestClientInitialization(t *testing.T) {
 			}
 		})
 	}
+
+	for _, tc := range unixTcs {
+		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 TestClientLimitsMaxConnections(t *testing.T) {