public function refresh($force = false) {
		if (!$force && time() - $this->last_fetch < $this->config['refresh_interval']) {
			return;
		}
		$clis = [];
		foreach ($this->conf['namespace'] as $v) {
			$clis[] = $this->getClient($v);
		}
		foreach ($clis as $cli) {
			$cli->recv();
			if ($cli->statusCode === 304) {
				continue;
			}
			$res = json_decode($cli->body, true);
			$ns = $res['namespaceName'];
			$this->last_key[$ns] = $res['releaseKey'];
			$this->update($ns, $res['configurations']);
		}
		$this->last_fetch = time();
	}