nats-io/nats-server · error

failed to be ready for connections after %s: %s

Error message

failed to be ready for connections after %s: %s

What it means

ReadyForConnections exceeded its wait deadline d: at least one subsystem in the readiness check set (client/nats/cluster/gateway/leafnode/websocket monitors etc.) did not report ok within the wait loop. The message aggregates each failed check with its error (format name(err)) or '(ok, but err)' for partial success. It means startup/monitoring is degraded — typically a bind failure (port in use, bad address) or an unreachable solicited route/gateway.

Source

Thrown at server/server.go:4040

		if d > 25*time.Millisecond {
			time.Sleep(25 * time.Millisecond)
		}
	}

	failed := make([]string, 0, len(chk))
	for name, inf := range chk {
		if inf.ok && inf.err != nil {
			failed = append(failed, fmt.Sprintf("%s(ok, but %s)", name, inf.err))
		}
		if !inf.ok && inf.err == nil {
			failed = append(failed, name)
		}
		if !inf.ok && inf.err != nil {
			failed = append(failed, fmt.Sprintf("%s(%s)", name, inf.err))
		}
	}

	return fmt.Errorf(
		"failed to be ready for connections after %s: %s",
		d, strings.Join(failed, ", "),
	)
}

// ReadyForConnections returns `true` if the server is ready to accept clients
// and, if routing is enabled, route connections. If after the duration
// `dur` the server is still not ready, returns `false`.
func (s *Server) ReadyForConnections(dur time.Duration) bool {
	return s.readyForConnections(dur) == nil
}

// Quick utility to function to tell if the server supports headers.
func (s *Server) supportsHeaders() bool {
	if s == nil {
		return false
	}
	return !(s.getOpts().NoHeaderSupport)

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Read the per-subsystem list in the error to find which listener failed and why
2. Free the occupied port or fix the bind address for the failing monitor
3. Verify network reachability of solicited routes/gateways/leaf remotes and retry startup

When it happens

Trigger: Thrown at server/server.go:4040 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/0452869bd62ea324. Report an issue: GitHub.