通过“定时刷盘、恢复”机制保证服务的可用性，相应逻辑封装在FailoverReactor中。

    1. /**
    2. * FailoverReactor
    3. *
    4. */
    5. public void init() {
    7.     // 故障转移
    8.     executorService.scheduleWithFixedDelay(new SwitchRefresher(), 0L, 5000L, TimeUnit.MILLISECONDS);
    10.     // 定时刷盘
    11.     executorService.scheduleWithFixedDelay(new DiskFileWriter(), 30, DAY_PERIOD_MINUTES, TimeUnit.MINUTES);
    13.     // backup file on startup if failover directory is empty.
    14.     executorService.schedule(new Runnable() {
    15.         @Override
    16.         public void run() {
    17.             try {
    18.                 File cacheDir = new File(failoverDir);
    20.                 if (!cacheDir.exists() && !cacheDir.mkdirs()) {
    21.                     throw new IllegalStateException("failed to create cache dir: " + failoverDir);
    22.                 }
    24.                 File[] files = cacheDir.listFiles();
    25.                 if (files == null || files.length <= 0) {
    26.                     new DiskFileWriter().run();
    27.                 }
    28.             } catch (Throwable e) {
    29.                 NAMING_LOGGER.error("[NA] failed to backup file on startup.", e);
    30.             }
    32.         }
    33.     }, 10000L, TimeUnit.MILLISECONDS);
    34. }

    1、DiskFileWriter
    定时将 Nacos Server端的信息写入容灾缓存目录下的文件中。

    2、SwitchRefresher
    从容灾目录下读取Nacos Server 信息，并进行恢复。
    It’s a switch file which need user create. It will be used when there are some problem between client and server. Users can create this file and set value = 1 to open client failover feature.
    It’s a old logic, maybe need to discuss how to optimize it.