fix(api): bind ssh gateway on ipv4

api/ssh_config.go

@@ -92,7 +92,9 @@ func newSSHGatewayConfig() (sshGatewayConfig, error) {
 
 	return sshGatewayConfig{
 		enabled:         true,
-		listenAddr:      fmt.Sprintf(":%d", listenPort),
+		// Bind explicitly on IPv4 so Kubernetes Service traffic can reach the SSH
+		// gateway even on clusters where an unspecified address becomes IPv6-only.
+		listenAddr:      fmt.Sprintf("0.0.0.0:%d", listenPort),
 		publicHost:      publicHost,
 		publicPort:      publicPort,
 		user:            user,

api/ssh_config_test.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"crypto/ed25519"
+	"crypto/rand"
+	"crypto/x509"
+	"encoding/pem"
+	"testing"
+)
+
+func TestNewSSHGatewayConfigBindsIPv4ListenAddr(t *testing.T) {
+	t.Setenv("SPRITZ_SSH_GATEWAY_ENABLED", "true")
+	t.Setenv("SPRITZ_SSH_PUBLIC_HOST", "ssh.example.com")
+	t.Setenv("SPRITZ_SSH_GATEWAY_PORT", "2022")
+	t.Setenv("SPRITZ_SSH_CA_KEY", newTestSSHPrivateKeyPEM(t))
+	t.Setenv("SPRITZ_SSH_HOST_KEY", newTestSSHPrivateKeyPEM(t))
+
+	cfg, err := newSSHGatewayConfig()
+	if err != nil {
+		t.Fatalf("newSSHGatewayConfig() error = %v", err)
+	}
+	if cfg.listenAddr != "0.0.0.0:2022" {
+		t.Fatalf("listenAddr = %q, want %q", cfg.listenAddr, "0.0.0.0:2022")
+	}
+}
+
+func newTestSSHPrivateKeyPEM(t *testing.T) string {
+	t.Helper()
+
+	_, privateKey, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatalf("generate ed25519 key: %v", err)
+	}
+
+	der, err := x509.MarshalPKCS8PrivateKey(privateKey)
+	if err != nil {
+		t.Fatalf("marshal pkcs8 private key: %v", err)
+	}
+
+	return string(pem.EncodeToMemory(&pem.Block{
+		Type:  "PRIVATE KEY",
+		Bytes: der,
+	}))
+}