Redis (ioredis) - 无法捕捉连接错误以优雅地处理它们

Question

我正在尝试优雅地处理 redis 错误，以便绕过错误并执行其他操作，而不是让我的应用崩溃。

但到目前为止，我不能只捕获 ioredis 抛出的异常，它绕过了我的 try/catch 并终止了当前进程。这种当前行为不允许我优雅地处理错误并从替代系统（而不是 redis）获取数据。

import { createLogger } from '@unly/utils-simple-logger';
import Redis from 'ioredis';
import epsagon from './epsagon';

const logger = createLogger({
  label: 'Redis client',
});

/**
 * Creates a redis client
 *
 * @param url Url of the redis client, must contain the port number and be of the form "localhost:6379"
 * @param password Password of the redis client
 * @param maxRetriesPerRequest By default, all pending commands will be flushed with an error every 20 retry attempts.
 *          That makes sure commands won't wait forever when the connection is down.
 *          Set to null to disable this behavior, and every command will wait forever until the connection is alive again.
 * @return {Redis}
 */
export const getClient = (url = process.env.REDIS_URL, password = process.env.REDIS_PASSWORD, maxRetriesPerRequest = 20) => {
  const client = new Redis(`redis://${url}`, {
    password,
    showFriendlyErrorStack: true, // See https://github.com/luin/ioredis#error-handling
    lazyConnect: true, // XXX Don't attempt to connect when initializing the client, in order to properly handle connection failure on a use-case basis
    maxRetriesPerRequest,
  });

  client.on('connect', function () {
    logger.info('Connected to redis instance');
  });

  client.on('ready', function () {
    logger.info('Redis instance is ready (data loaded from disk)');
  });

  // Handles redis connection temporarily going down without app crashing
  // If an error is handled here, then redis will attempt to retry the request based on maxRetriesPerRequest
  client.on('error', function (e) {
    logger.error(`Error connecting to redis: "${e}"`);
    epsagon.setError(e);

    if (e.message === 'ERR invalid password') {
      logger.error(`Fatal error occurred "${e.message}". Stopping server.`);
      throw e; // Fatal error, don't attempt to fix
    }
  });

  return client;
};

我正在模拟一个错误的密码/url，以便查看 redis 在配置错误时的反应。我已将 lazyConnect 设置为 true 以处理调用者的错误。

但是，当我将 url 定义为 localhoste:6379 （而不是 localhost:6379） 时，我收到以下错误：

server 2019-08-10T19:44:00.926Z [Redis client] error:  Error connecting to redis: "Error: getaddrinfo ENOTFOUND localhoste localhoste:6379"
(x 20)
server 2019-08-10T19:44:11.450Z [Read cache] error:  Reached the max retries per request limit (which is 20). Refer to "maxRetriesPerRequest" option for details.

这是我的代码：

  // Fetch a potential query result for the given query, if it exists in the cache already
  let cachedItem;

  try {
    cachedItem = await redisClient.get(queryString); // This emit an error on the redis client, because it fails to connect (that's intended, to test the behaviour)
  } catch (e) {
    logger.error(e); // It never goes there, as the error isn't "thrown", but rather "emitted" and handled by redis its own way
    epsagon.setError(e);
  }

  // If the query is cached, return the results from the cache
  if (cachedItem) {
    // return item
  } else {} // fetch from another endpoint (fallback backup)

我的理解是redis错误是通过client.emit('error', error)处理的，是异步的，被调用者不会抛出错误，也就是不允许调用者使用try/catch处理错误。

是否应该以非常特殊的方式处理 redis 错误？难道不能像我们通常处理大多数错误那样捕获它们吗？

此外，redis 在抛出致命异常（进程停止）之前似乎重试了 20 次连接（默认情况下）。但我想处理任何异常并以我自己的方式处理它。

我通过提供错误的连接数据测试了 redis 客户端的行为，这使得无法连接，因为该 url 上没有可用的 redis 实例，我的目标是最终捕获各种 redis 错误并优雅地处理它们。

Answer 1

客户端 Redis 对象上的连接错误 are reported as an error event。

根据"Auto-reconnect" section of the docs，ioredis 会在与 Redis 的连接丢失（或者可能是一开始就无法建立）时自动尝试重新连接。只有在 maxRetriesPerRequest 尝试之后，未决命令才会“因错误而被刷新”，即在此处到达 catch：

  try {
    cachedItem = await redisClient.get(queryString); // This emit an error on the redis client, because it fails to connect (that's intended, to test the behaviour)
  } catch (e) {
    logger.error(e); // It never goes there, as the error isn't "thrown", but rather "emitted" and handled by redis its own way
    epsagon.setError(e);
  }

由于您在第一个错误时停止程序：

  client.on('error', function (e) {
    // ...
    if (e.message === 'ERR invalid password') {
      logger.error(`Fatal error occurred "${e.message}". Stopping server.`);
      throw e; // Fatal error, don't attempt to fix

...重试和随后的“错误刷新”永远没有机会运行。

忽略client.on('error'中的错误，你应该会得到await redisClient.get()返回的错误。

Answer 2

这是我的团队在 TypeScript 项目中使用 IORedis 所做的：

  let redis;
  const redisConfig: Redis.RedisOptions = {
    port: parseInt(process.env.REDIS_PORT, 10),
    host: process.env.REDIS_HOST,
    autoResubscribe: false,
    lazyConnect: true,
    maxRetriesPerRequest: 0, // <-- this seems to prevent retries and allow for try/catch
  };

  try {

    redis = new Redis(redisConfig);

    const infoString = await redis.info();
    console.log(infoString)

  } catch (err) {

    console.log(chalk.red('Redis Connection Failure '.padEnd(80, 'X')));
    console.log(err);
    console.log(chalk.red(' Redis Connection Failure'.padStart(80, 'X')));
    // do nothing

  } finally {
    await redis.disconnect();
  }