fix(backend): improve API version detection with retry logic for health probes

Signed-off-by: Noste <83548733+Noooste@users.noreply.github.com>

backend/internal/services/admin_factory.go

@@ -39,8 +39,14 @@ type AdminServiceResult struct {
 	APIVersion   string
 }
 
+// errProbeNotFound means the probed route returned 404. Garage v2.x also serves
+// /v1/health, so a 404 on /v2 is the only reliable "this is a v1 server" signal.
+var errProbeNotFound = errors.New("probe endpoint not found")
+
 func NewAdminService(cfg *config.GarageConfig, logLevel string) (*AdminServiceResult, error) {
-	if err := probeEndpoint(cfg, "/v2/GetClusterHealth"); err == nil {
+	// retry so a startup fails doesn't lock us to a v1 client.
+	err := probeEndpointWithRetry(cfg, "/v2/GetClusterHealth")
+	if err == nil {
 		logger.Info().Str("api_version", "v2").Msg("Detected Garage admin API v2")
 		svc := NewGarageV2AdminService(cfg, logLevel)
 		return &AdminServiceResult{
@@ -50,7 +56,17 @@ func NewAdminService(cfg *config.GarageConfig, logLevel string) (*AdminServiceRe
 		}, nil
 	}
 
-	if err := probeEndpoint(cfg, "/v1/health"); err == nil {
+	// only fall back to v1 on a real 404
+	// other errors mean the server is up but the probe failed transiently; picking v1 against
+	// a v2.x server breaks /v1/status with "v1/ endpoint is no longer supported" (issue #78).
+	if !errors.Is(err, errProbeNotFound) {
+		return nil, fmt.Errorf(
+			"could not detect Garage admin API version at %s: %w. Ensure Garage v1.1+ is running and the admin API is reachable",
+			cfg.AdminEndpoint, err,
+		)
+	}
+
+	if err := probeEndpointWithRetry(cfg, "/v1/health"); err == nil {
 		logger.Info().
 			Str("api_version", "v1").
 			Msg("Detected Garage admin API v1 — cluster statistics and per-node details will be unavailable")
@@ -68,6 +84,26 @@ func NewAdminService(cfg *config.GarageConfig, logLevel string) (*AdminServiceRe
 	)
 }
 
+const probeAttempts = 4
+
+// probeEndpointWithRetry retries transient failures with backoff, but returns a
+// 404 immediately, a missing route won't appear on a retry.
+func probeEndpointWithRetry(cfg *config.GarageConfig, path string) error {
+	var err error
+	backoff := 250 * time.Millisecond
+	for attempt := range probeAttempts {
+		err = probeEndpoint(cfg, path)
+		if err == nil || errors.Is(err, errProbeNotFound) {
+			return err
+		}
+		if attempt < probeAttempts-1 {
+			time.Sleep(backoff)
+			backoff *= 2
+		}
+	}
+	return err
+}
+
 func probeEndpoint(cfg *config.GarageConfig, path string) error {
 	session := azuretls.NewSession()
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
@@ -86,6 +122,9 @@ func probeEndpoint(cfg *config.GarageConfig, path string) error {
 	}
 	defer resp.RawBody.Close()
 
+	if resp.StatusCode == http.StatusNotFound {
+		return fmt.Errorf("probe %s returned status 404: %w", path, errProbeNotFound)
+	}
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
 		return fmt.Errorf("probe %s returned status %d", path, resp.StatusCode)
 	}