vitessio/vitess · error

failed to render config to tempfile: %v

Error message

failed to render config to tempfile: %v

What it means

The viperutil debug HTTP handler renders the current config to a temp file because viper lacks WriteConfigTo(w io.Writer). If os.CreateTemp fails, it returns 500 with 'failed to render config to tempfile'. This means the environment cannot supply a temp file at all.

Source

Thrown at go/viperutil/debug/handler.go:65

		acl.SendError(w, err)
		return
	}

	v := registry.Combined()
	format := strings.ToLower(r.URL.Query().Get("format"))
	switch {
	case format == "":
		v.DebugTo(w)
	case slice.Any(viper.SupportedExts, func(ext string) bool { return ext == format }):
		// Got a supported format; write the config to a tempfile in that format,
		// then copy it to the response.
		//
		// (Sadly, viper does not yet have a WriteConfigTo(w io.Writer), so we have
		// to do this little hacky workaround).
		v.SetConfigType(format)
		tmp, err := os.CreateTemp("", "viper_debug")
		if err != nil {
			http.Error(w, fmt.Sprintf("failed to render config to tempfile: %v", err), http.StatusInternalServerError)
			return
		}
		defer os.Remove(tmp.Name())

		if err := v.WriteConfigAs(tmp.Name()); err != nil {
			http.Error(w, fmt.Sprintf("failed to render config to tempfile: %v", err), http.StatusInternalServerError)
			return
		}

		if _, err := io.Copy(w, tmp); err != nil {
			http.Error(w, fmt.Sprintf("failed to write rendered config: %v", err), http.StatusInternalServerError)
			return
		}
	default:
		http.Error(w, "unsupported config format", http.StatusBadRequest)
	}
}

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Ensure TMPDIR points to a writable directory (or mount a writable tmpfs at /tmp) and restart the process.
2. Free disk space on the partition backing the temp directory.
3. Check permissions on the temp directory for the process user.
4. As a workaround, view the config via other debug endpoints or logs if temp files cannot be enabled.

Example fix

// before (docker run)
docker run --read-only vitess/lite ...
// after
docker run --read-only --tmpfs /tmp:rw,size=64m vitess/lite ...

tmp := os.TempDir()
if fi, err := os.Stat(tmp); err != nil || !fi.IsDir() {
	return fmt.Errorf("temp dir %s unusable: %v", tmp, err)
}
test, err := os.CreateTemp(tmp, "probe")
if err != nil {
	return err
}
test.Close()
os.Remove(test.Name())

When it happens

Trigger: Hitting the debug config endpoint (HandlerFunc) when os.CreateTemp("", "viper_debug") fails — typically /tmp not existing, being full, or permission denied for the process.

Common situations: Containers with read-only root filesystem and no writable TMPDIR; disk-full on /tmp; TMPDIR pointing to a nonexistent directory; hardened sandboxes blocking temp file creation.

Related errors

• could not create temp file: %v
• could not read existing file %v: %v
• unsupported config format
• cell mode should be handled by the gateway, not the balancer
• failed to create file-based writer for --opentsdb-uri %s: %v

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/8d9c46c6b0db7925. Report an issue: GitHub.