private Optional<Instant> rotatedAt(Path path) {
        String[] parts = path.getFileName().toString().split("-", 2);
        if (parts.length != 2) return Optional.empty();
        return Optional.of(LocalDateTime.from(NginxPath.ROTATED_SUFFIX_FORMAT.parse(parts[1])).toInstant(ZoneOffset.UTC));
    }
Returns the time given path was rotated
routing-generator/src/main/java/com/yahoo/vespa/hosted/routing/nginx/Nginx.java