redis集群故障分析

迷南。 2022-09-25 13:19 176阅读 0赞

**故障表象：**  
业务层面显示提示查询redis失败  
  
  
**集群组成：**  
3主3从，每个节点的数据有8GB  
  
  
**机器分布：**  
在同一个机架中，  
xx.x.xxx.199  
xx.x.xxx.200  
xx.x.xxx.201  
  
  
**redis-server进程状态：**  
通过命令ps -eo pid,lstart | grep $pid，  
发现进程已经持续运行了3个月  
  
  
**发生故障前集群的节点状态：**  
xx.x.xxx.200:8371(bedab2c537fe94f8c0363ac4ae97d56832316e65) master  
xx.x.xxx.199:8373(792020fe66c00ae56e27cd7a048ba6bb2b67adb6) slave  
  
xx.x.xxx.201:8375(5ab4f85306da6d633e4834b4d3327f45af02171b) master  
xx.x.xxx.201:8372(826607654f5ec81c3756a4a21f357e644efe605a) slave  
  
xx.x.xxx.199:8370(462cadcb41e635d460425430d318f2fe464665c5) master  
xx.x.xxx.200:8374(1238085b578390f3c8efa30824fd9a4baba10ddf) slave  
  
  
**---------------------------------下面是日志分析--------------------------------------  
  
步1：**  
主节点8371失去和从节点8373的连接：  
46590:M 09 Sep 18:57:51.379 \# Connection with slave xx.x.xxx.199:8373 lost.  
  
**步2：**  
主节点8370/8375判定8371失联：  
42645:M 09 Sep 18:57:50.117 \* Marking node bedab2c537fe94f8c0363ac4ae97d56832316e65 as failing (quorum reached).  
  
**步3：**  
从节点8372/8373/8374收到主节点8375说8371失联：  
46986:S 09 Sep 18:57:50.120 \* FAIL message received from 5ab4f85306da6d633e4834b4d3327f45af02171b about bedab2c537fe94f8c0363ac4ae97d56832316e65  
  
**步4：**  
主节点8370/8375授权8373升级为主节点转移：  
42645:M 09 Sep 18:57:51.055 \# Failover auth granted to 792020fe66c00ae56e27cd7a048ba6bb2b67adb6 for epoch 16  
  
**步5：**  
原主节点8371修改自己的配置，成为8373的从节点：  
46590:M 09 Sep 18:57:51.488 \# Configuration change detected. Reconfiguring myself as a replica of 792020fe66c00ae56e27cd7a048ba6bb2b67adb6  
  
**步6：**  
主节点8370/8375/8373明确8371失败状态：  
42645:M 09 Sep 18:57:51.522 \* Clear FAIL state for node bedab2c537fe94f8c0363ac4ae97d56832316e65: master without slots is reachable again.  
  
**步7：**  
新从节点8371开始从新主节点8373，第一次全量同步数据：  
8373日志：：  
4255:M 09 Sep 18:57:51.906 \* Full resync requested by slave xx.x.xxx.200:8371  
4255:M 09 Sep 18:57:51.906 \* Starting BGSAVE for SYNC with target: disk  
4255:M 09 Sep 18:57:51.941 \* Background saving started by pid 5230  
  
8371日志：：  
46590:S 09 Sep 18:57:51.948 \* Full resync from master: d7751c4ebf1e63d3baebea1ed409e0e7243a4423:440721826993  
  
**步8：**  
主节点8370/8375判定8373(新主)失联：  
42645:M 09 Sep 18:58:00.320 \* Marking node 792020fe66c00ae56e27cd7a048ba6bb2b67adb6 as failing (quorum reached).  
  
**步9：**  
主节点8370/8375判定8373(新主)恢复：  
60295:M 09 Sep 18:58:18.181 \* Clear FAIL state for node 792020fe66c00ae56e27cd7a048ba6bb2b67adb6: is reachable again and nobody is serving its slots after some time.  
  
**步10：**  
主节点8373完成全量同步所需要的BGSAVE操作：  
5230:C 09 Sep 18:59:01.474 \* DB saved on disk  
5230:C 09 Sep 18:59:01.491 \* RDB: 7112 MB of memory used by copy-on-write  
4255:M 09 Sep 18:59:01.877 \* Background saving terminated with success  
  
**步11：**  
从节点8371开始从主节点8373接收到数据：  
46590:S 09 Sep 18:59:02.263 \* MASTER <-> SLAVE sync: receiving 2657606930 bytes from master  
  
**步12：**  
主节点8373发现从节点8371对output buffer作了限制：  
4255:M 09 Sep 19:00:19.014 \# Client id=14259015 addr=xx.x.xxx.200:21772 fd=844 name= age=148 idle=148 flags=S db=0 sub=0 psub=0 multi=-1 qbuf=0 qbuf-free=0 obl=16349 oll=4103 omem=95944066 events=rw cmd=psync scheduled to be closed ASAP for overcoming of output buffer limits.  
4255:M 09 Sep 19:00:19.015 \# Connection with slave xx.x.xxx.200:8371 lost.  
  
**步13：**  
从节点8371从主节点8373同步数据失败，连接断了，第一次全量同步失败：  
46590:S 09 Sep 19:00:19.018 \# I/O error trying to sync with MASTER: connection lost  
46590:S 09 Sep 19:00:20.102 \* Connecting to MASTER xx.x.xxx.199:8373  
46590:S 09 Sep 19:00:20.102 \* MASTER <-> SLAVE sync started  
  
**步14：**  
从节点8371重新开始同步，连接失败，主节点8373的连接数满了：  
46590:S 09 Sep 19:00:21.103 \* Connecting to MASTER xx.x.xxx.199:8373  
46590:S 09 Sep 19:00:21.103 \* MASTER <-> SLAVE sync started  
46590:S 09 Sep 19:00:21.104 \* Non blocking connect for SYNC fired the event.  
46590:S 09 Sep 19:00:21.104 \# Error reply to PING from master: '-ERR max number of clients reached'  
  
**步15：**  
从节点8371重新连上主节点8373，第二次开始全量同步：  
8371日志：  
46590:S 09 Sep 19:00:49.175 \* Connecting to MASTER xx.x.xxx.199:8373  
46590:S 09 Sep 19:00:49.175 \* MASTER <-> SLAVE sync started  
46590:S 09 Sep 19:00:49.175 \* Non blocking connect for SYNC fired the event.  
46590:S 09 Sep 19:00:49.176 \* Master replied to PING, replication can continue...  
46590:S 09 Sep 19:00:49.179 \* Partial resynchronization not possible (no cached master)  
46590:S 09 Sep 19:00:49.501 \* Full resync from master: d7751c4ebf1e63d3baebea1ed409e0e7243a4423:440780763454  
  
8373日志：  
4255:M 09 Sep 19:00:49.176 \* Slave xx.x.xxx.200:8371 asks for synchronization  
4255:M 09 Sep 19:00:49.176 \* Full resync requested by slave xx.x.xxx.200:8371  
4255:M 09 Sep 19:00:49.176 \* Starting BGSAVE for SYNC with target: disk  
4255:M 09 Sep 19:00:49.498 \* Background saving started by pid 18413  
18413:C 09 Sep 19:01:52.466 \* DB saved on disk  
18413:C 09 Sep 19:01:52.620 \* RDB: 2124 MB of memory used by copy-on-write  
4255:M 09 Sep 19:01:53.186 \* Background saving terminated with success  
  
**步16：**  
从节点8371同步数据成功，开始加载经内存：  
46590:S 09 Sep 19:01:53.190 \* MASTER <-> SLAVE sync: receiving 2637183250 bytes from master  
46590:S 09 Sep 19:04:51.485 \* MASTER <-> SLAVE sync: Flushing old data  
46590:S 09 Sep 19:05:58.695 \* MASTER <-> SLAVE sync: Loading DB in memory  
  
**步17：**  
集群恢复正常：  
42645:M 09 Sep 19:05:58.786 \* Clear FAIL state for node bedab2c537fe94f8c0363ac4ae97d56832316e65: slave is reachable again.  
  
**步18：**  
从节点8371同步数据成功，耗时7分钟：  
46590:S 09 Sep 19:08:19.303 \* MASTER <-> SLAVE sync: Finished with success  
  
  
**8371失联原因分析：**  
由于几台机器在同一个机架，不太可能发生网络中断的情况，  
于是通过SLOWLOG GET命令查看了慢查询日志，发现有一个KEYS命令被执行了，耗时8.3秒，  
再查看集群节点超时设置，发现是5s(cluster-node-timeout 5000)

**出现节点失联的原因：**  
客户端执行了耗时1条8.3s的命令，  
2016/9/9 18:57:43 开始执行KEYS命令  
2016/9/9 18:57:50 8371被判断失联（redis日志）  
2016/9/9 18:57:51 执行完KEYS命令  
  
  
**总结来说，有以下几个问题：**  
1.由于cluster-node-timeout设置比较短，慢查询KEYS导致了集群判断节点8371失联  
2.由于8371失联，导致8373升级为主，开始主从同步  
3.由于配置client-output-buffer-limit的限制，导致第一次全量同步失败了  
4.又由于PHP客户端的连接池有问题，疯狂连接服务器，产生了类似SYN攻击的效果  
5.第一次全量同步失败后，从节点重连主节点花了30秒（超过了最大连接数1w）  
  
  
**关于client-output-buffer-limit参数：**

# The syntax of every client-output-buffer-limit directive is the following:
    #
    # client-output-buffer-limit <class> <hard limit> <soft limit> <soft seconds>
    #
    # A client is immediately disconnected once the hard limit is reached, or if
    # the soft limit is reached and remains reached for the specified number of
    # seconds (continuously).
    # So for instance if the hard limit is 32 megabytes and the soft limit is
    # 16 megabytes / 10 seconds, the client will get disconnected immediately
    # if the size of the output buffers reach 32 megabytes, but will also get
    # disconnected if the client reaches 16 megabytes and continuously overcomes
    # the limit for 10 seconds.
    #
    # By default normal clients are not limited because they don't receive data
    # without asking (in a push way), but just after a request, so only
    # asynchronous clients may create a scenario where data is requested faster
    # than it can read.
    #
    # Instead there is a default limit for pubsub and slave clients, since
    # subscribers and slaves receive data in a push fashion.
    #
    # Both the hard or the soft limit can be disabled by setting them to zero.
    client-output-buffer-limit normal 0 0 0
    client-output-buffer-limit slave 256mb 64mb 60
    client-output-buffer-limit pubsub 32mb 8mb 60

**采取措施：**

1.单实例的切割到4G以下，否则发生主从切换会耗时很长

2.调整client-output-buffer-limit参数，防止同步进行到一半失败

3.调整cluster-node-timeout，不能少于15s

4.禁止任何耗时超过cluster-node-timeout的慢查询，因为会导致主从切换

5.修复客户端类似SYN攻击的疯狂连接方式

原文出自：[http://blog.csdn.net/daiyudong2020/article/details/52496725][http_blog.csdn.net_daiyudong2020_article_details_52496725]

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[http_blog.csdn.net_daiyudong2020_article_details_52496725]: http://blog.csdn.net/daiyudong2020/article/details/52496725