Redis (ioredis) - 無法捕獲連接錯誤以優雅地處理它們

Question

我正在嘗試優雅地處理 redis 錯誤，以便繞過錯誤並執行其他操作，而不是使我的應用程序崩潰。

但到目前為止，我不能只捕獲ioredis拋出的異常，它繞過我的try/catch並終止當前進程。 這種當前的行為不允許我優雅地處理錯誤，也不允許我從替代系統（而不是 redis）中獲取數據。

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;
};

我正在模擬錯誤的密碼/url，以便查看 redis 在配置錯誤時的反應。 我已將lazyConnect設置為true以處理調用方的錯誤。

但是，當我將 url 定義為localhoste:6379 (而不是localhost:6379 ) 時，我收到以下錯誤：

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.

這是我的代碼：

  // 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 錯誤是通過client.emit('error', error) ，這是異步的，被調用者不會拋出錯誤，這不允許調用者使用 try/catch 處理錯誤。

應該以非常特殊的方式處理 redis 錯誤嗎？ 難道不能像我們通常對大多數錯誤所做的那樣捕獲它們嗎？

此外，在拋出致命異常（進程停止）之前，redis 似乎重試了 20 次連接（默認情況下）。 但我想處理任何異常並以我自己的方式處理它。

我已經通過提供錯誤的連接數據來測試 redis 客戶端的行為，這使得無法連接，因為該 url 上沒有可用的 redis 實例，我的目標是最終捕獲各種 redis 錯誤並優雅地處理它們。

Answer 1

連接錯誤在客戶端Redis對象上報告為error事件。

根據文檔的“自動重新連接”部分，ioredis 將在與 Redis 的連接丟失時自動嘗試重新連接（或者，大概無法首先建立）。 只有在maxRetriesPerRequest嘗試之后，掛起的命令才會“被錯誤刷新”，即在這里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);
  }

由於您在第一個錯誤時停止程序：

  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

...重試和隨后的“因錯誤而刷新”永遠沒有機會運行。

忽略client.on('error' ，你應該得到從await redisClient.get()返回的錯誤。

Answer 2

以下是我的團隊在 TypeScript 項目中使用 IORedis 所做的事情：

  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();
  }