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MySQL参数max_connect_errors分析释疑

2018-02-02 16:36  潇湘隐者  阅读(20945)  评论(5编辑  收藏

 

最近一MySQL服务器,由于一些特殊因素遇到ERROR 1129 (00000): Host 'xxx' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts',在问题解决后,在详细了解参数max_connect_errors的过程中,有些不同网络资料的矛盾描述确实让我有点迷惑和混淆(关于这个错误,本质原因是因为同一个IP在短时间内产生太多中断的数据库连接(超过max_connect_errors的最大值)而导致的),下面介绍我的探索问题、分析问题、释疑的一个过程。

 

首先,我在网上搜索了一些资料,不少资料信誓旦旦的介绍,密码输入错误的尝试次数超过max_connect_errors变量,MySQL就会阻塞这个客户端登录,然后我找到了官方资料关于max_connect_errors的介绍,如下所示,MySQL 5.6/5.7的介绍一致

 

 

If more than this many successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. You can unblock blocked hosts by flushing the host cache. To do so, issue a FLUSH HOSTS statement or execute a mysqladmin flush-hosts command. If a connection is established successfully within fewer than max_connect_errors attempts after a previous connection was interrupted, the error count for the host is cleared to zero. However, once a host is blocked, flushing the host cache is the only way to unblock it. The default is 100.

 

如上所示,翻译出来的话,大致如下:如果MySQL服务器连续接收到了来自于同一个主机的请求,而且这些连续的请求全部都没有成功的建立连接就被中断了,当这些连续的请求的累计值大于max_connect_errors的设定值时,MySQL服务器就会阻止这台主机后续的所有请求。相信一开始你看到这些资料,也会被many successive connection requests from a host are interrupted without a successful connection给弄懵,其实这个就是因为由于网络异常而中止数据库连接。网上搜索到这么一个资料:

 

There seems to be confusion around that variable. It does not really block hosts for repeated invalid passwords but for aborted connections due to network errors.

 

 

 

好吧,那么我们自己动手实验验证一下,就能弄明白到底那个是正确的。在MySQL数据库里面创建一个test账号,然后我们将max_connect_errors变量设置为3.

 

 

 

mysql> show variables like '%max_connect_errors%';
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| max_connect_errors | 100   |
+--------------------+-------+
1 row in set (0.00 sec)
 
mysql> set global max_connect_errors=3;
Query OK, 0 rows affected (0.00 sec)
 
mysql> show variables like '%max_connect_error%';
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| max_connect_errors | 3     |
+--------------------+-------+
1 row in set (0.00 sec)
 

 

 

然后我们在另外一台测试机器,以错误的密码去连接这个MySQL数据库,如下所示,即使前面输入了三次错误密码,第四次输入是也没有碰到上面错误。那么可以排除这个变量与密码错误输入有关系。

 

 

[root@mytestlnx02 tmp]# mysql -h10.20.57.24 -utest -p

Enter password:

ERROR 1045 (28000): Access denied for user 'test'@'mytestlnx02' (using password: YES)

[root@mytestlnx02 tmp]# mysql -h10.20.57.24 -utest -p

Enter password:

ERROR 1045 (28000): Access denied for user 'test'@'mytestlnx02' (using password: YES)

[root@mytestlnx02 tmp]# mysql -h10.20.57.24 -utest -p

Enter password:

ERROR 1045 (28000): Access denied for user 'test'@'mytestlnx02' (using password: YES)

[root@mytestlnx02 tmp]# mysql -h10.20.57.24 -utest -p

Enter password:

ERROR 1045 (28000): Access denied for user 'test'@'mytestlnx02' (using password: YES)

[root@mytestlnx02 tmp]#

 

 

其实,关于某个IP输入了错误密码,MySQL会在performance_schema数据库下的host_cache表中记录。它会累计记录在COUNT_AUTHENTICATION_ERRORS字段,如下所示:

 

 

mysql> use performance_schema;
Database changed
mysql> select * from host_cache\G;
*************************** 1. row ***************************
                                        IP: 192.168.27.180
                                      HOST: gettestlnx02
                            HOST_VALIDATED: YES
                        SUM_CONNECT_ERRORS: 0
                 COUNT_HOST_BLOCKED_ERRORS: 0
           COUNT_NAMEINFO_TRANSIENT_ERRORS: 0
           COUNT_NAMEINFO_PERMANENT_ERRORS: 0
                       COUNT_FORMAT_ERRORS: 0
           COUNT_ADDRINFO_TRANSIENT_ERRORS: 0
           COUNT_ADDRINFO_PERMANENT_ERRORS: 0
                       COUNT_FCRDNS_ERRORS: 0
                     COUNT_HOST_ACL_ERRORS: 0
               COUNT_NO_AUTH_PLUGIN_ERRORS: 0
                  COUNT_AUTH_PLUGIN_ERRORS: 0
                    COUNT_HANDSHAKE_ERRORS: 0
                   COUNT_PROXY_USER_ERRORS: 0
               COUNT_PROXY_USER_ACL_ERRORS: 0
               COUNT_AUTHENTICATION_ERRORS: 4
                          COUNT_SSL_ERRORS: 0
         COUNT_MAX_USER_CONNECTIONS_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS: 0
             COUNT_DEFAULT_DATABASE_ERRORS: 0
                 COUNT_INIT_CONNECT_ERRORS: 0
                        COUNT_LOCAL_ERRORS: 0
                      COUNT_UNKNOWN_ERRORS: 0
                                FIRST_SEEN: 2018-01-31 16:28:19
                                 LAST_SEEN: 2018-01-31 16:28:26
                          FIRST_ERROR_SEEN: 2018-01-31 16:28:19
                           LAST_ERROR_SEEN: 2018-01-31 16:28:26
1 row in set (0.00 sec)
 
ERROR: 
No query specified
 

 

clip_image001

 

 

 

官方资料介绍,host_cache的字段是统计被视为阻塞的连接错误的数量(根据max_connect_errors系统变量进行评估)。 只计算协议握手错误,并且仅用于通过验证的主机(HOST_VALIDATED = YES)。

 

SUM_CONNECT_ERRORS

The number of connection errors that are deemed “blocking” (assessed against the max_connect_errors system variable). Only protocol handshake errors are counted, and only for hosts that passed validation (HOST_VALIDATED = YES).

 

MySQL客户端与数据库建立连接需要发起三次握手协议,正常情况下,这个时间非常短,但是一旦网络异常,网络超时等因素出现,就会导致这个握手协议无法完成,MySQL有个参数connect_timeout,它是MySQL服务端进程mysqld等待连接建立完成的时间,单位为秒。如果超过connect_timeout时间范围内,仍然无法完成协议握手话,MySQL客户端会收到异常,异常消息类似于: Lost connection to MySQL server at 'XXX', system error: errno,该变量默认是10秒: 

 

 

 

mysql> show variables like 'connect_timeout';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| connect_timeout | 10    |
+-----------------+-------+
1 row in set (0.00 sec)
 
mysql> 

 

 

 

那么我们就构造一个网络超时引起的数据库连接被中断案例吧,我们用Linux下的netemtc命令模拟构造出复杂环境下的网络传输延时案例,如下设置后,此时从测试服务器去访问MySQL服务器,都会出现延时11秒:

 

 

 

 

[root@gettestlnx02 ~]# ping 10.20.57.24

PING 10.20.57.24 (10.20.57.24) 56(84) bytes of data.

64 bytes from 10.20.57.24: icmp_seq=1 ttl=62 time=0.251 ms

64 bytes from 10.20.57.24: icmp_seq=2 ttl=62 time=0.330 ms

64 bytes from 10.20.57.24: icmp_seq=3 ttl=62 time=0.362 ms

64 bytes from 10.20.57.24: icmp_seq=4 ttl=62 time=0.316 ms

64 bytes from 10.20.57.24: icmp_seq=5 ttl=62 time=0.281 ms

64 bytes from 10.20.57.24: icmp_seq=6 ttl=62 time=0.377 ms

^C

--- 10.20.57.24 ping statistics ---

6 packets transmitted, 6 received, 0% packet loss, time 5716ms

rtt min/avg/max/mdev = 0.251/0.319/0.377/0.047 ms

[root@gettestlnx02 ~]# tc qdisc add dev eth0 root netem delay 11000ms

[root@gettestlnx02 ~]# ping 10.20.57.24

PING 10.20.57.24 (10.20.57.24) 56(84) bytes of data.

64 bytes from 10.20.57.24: icmp_seq=1 ttl=62 time=11000 ms

64 bytes from 10.20.57.24: icmp_seq=2 ttl=62 time=11000 ms

64 bytes from 10.20.57.24: icmp_seq=3 ttl=62 time=11000 ms

64 bytes from 10.20.57.24: icmp_seq=4 ttl=62 time=11000 ms

64 bytes from 10.20.57.24: icmp_seq=5 ttl=62 time=11000 ms

64 bytes from 10.20.57.24: icmp_seq=6 ttl=62 time=11000 ms

64 bytes from 10.20.57.24: icmp_seq=7 ttl=62 time=11000 ms

 

 

clip_image002

 

 

 

我们在测试服务器gettestlnx02连接MySQL数据库,如下所示(注意,如果你是在通过ssh连接这台服务器的话,此时在gettestlnx02上操作会相当慢。当然你也可以在MySQL服务器模拟网络延时,或者你将connect_timeout和网络延时都设小一点)

 

 

 

[root@gettestlnx02 ~]# mysql -h10.20.57.24 -utest -p

Enter password:

ERROR 2013 (HY000): Lost connection to MySQL server at 'reading authorization packet', system error: 0

[root@gettestlnx02 ~]#

 

 

 

如上所示,由于网络延时超过10秒,导致连接MySQL失败,此时,你在MySQL服务器上查询host_cache表时,那么你就会看到SUM_CONNECT_ERRORS变成1了,COUNT_HANDSHAKE_ERRORS也变成了1.

 

 

 

 

clip_image003

 

 

那么我们反复这样折腾三次,那么你会看到SUM_CONNECT_ERRORS变成3了,COUNT_HANDSHAKE_ERRORS也变成了3.

 

 

 

 

mysql> select * from host_cache\G;
*************************** 1. row ***************************
                                        IP: 192.168.27.180
                                      HOST: gettestlnx02
                            HOST_VALIDATED: YES
                        SUM_CONNECT_ERRORS: 3
                 COUNT_HOST_BLOCKED_ERRORS: 1
           COUNT_NAMEINFO_TRANSIENT_ERRORS: 0
           COUNT_NAMEINFO_PERMANENT_ERRORS: 0
                       COUNT_FORMAT_ERRORS: 0
           COUNT_ADDRINFO_TRANSIENT_ERRORS: 0
           COUNT_ADDRINFO_PERMANENT_ERRORS: 0
                       COUNT_FCRDNS_ERRORS: 0
                     COUNT_HOST_ACL_ERRORS: 0
               COUNT_NO_AUTH_PLUGIN_ERRORS: 0
                  COUNT_AUTH_PLUGIN_ERRORS: 0
                    COUNT_HANDSHAKE_ERRORS: 3
                   COUNT_PROXY_USER_ERRORS: 0
               COUNT_PROXY_USER_ACL_ERRORS: 0
               COUNT_AUTHENTICATION_ERRORS: 4
                          COUNT_SSL_ERRORS: 0
         COUNT_MAX_USER_CONNECTIONS_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS: 0
             COUNT_DEFAULT_DATABASE_ERRORS: 0
                 COUNT_INIT_CONNECT_ERRORS: 0
                        COUNT_LOCAL_ERRORS: 0
                      COUNT_UNKNOWN_ERRORS: 0
                                FIRST_SEEN: 2018-01-31 16:28:19
                                 LAST_SEEN: 2018-01-31 17:02:10
                          FIRST_ERROR_SEEN: 2018-01-31 16:28:19
                           LAST_ERROR_SEEN: 2018-01-31 17:02:10
1 row in set (0.00 sec)
 
ERROR: 
No query specified

 

 

 

 

然后我们用netemtc 命令在测试服务器上取消网络延迟模拟,然后去测试连接MySQL数据库,如下测试所示:

 

 

[root@gettestlnx02 ~]# tc qdisc del dev eth0 root netem delay 11000ms

[root@gettestlnx02 ~]# mysql -h10.20.57.24 -utest -p

Enter password:

ERROR 1129 (HY000): Host '192.168.27.180' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'

[root@gettestlnx02 ~]#

 

 

 

clip_image004

 

 

 

 

此时就能构造出ERROR 1129 (HY000): Host '192.168.27.180' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'错误了。

 

 

 

 

 

解决方案

 

 

 

 解决ERROR 1129 (00000): Host 'xxx' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts'这个错误的方法比较多,不过有些方案都是临时方案。临时方案是指标不治本。关键还是需要解决网络错误(这个往往需要求助网络管理人员或系统管理员)

 

解决方法:

 

 

1、将变量max_connection_errors的值设置为一个更大的值

 

 

mysql> show variables like 'max_connect_errors';
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| max_connect_errors | 3     |
+--------------------+-------+
1 row in set (0.01 sec)
 
mysql> set global max_connect_errors=150;
Query OK, 0 rows affected (0.00 sec)
 
mysql> 
 

 

这个临时方案只是延迟触发IP被禁止访问的条件而已,而且在复杂情况或高并发的情况下,需要设置一个很大的值,否则很容易就会再次被触发。另外,变量只对当前环境生效,如果重启就会失效,如果需要永久有效,可以在my.cnf配置文件里面配置。

 

 

2:使用flush hosts

 

mysql> flush hosts;

Query OK, 0 rows affected (0.00 sec)

 

mysql> select * from performance_schema.host_cache;

Empty set (0.00 sec)

 

mysql>

 

当然你也可以mysqladmin flush-hosts 命令清理一下hosts cache信息

 

[root@DB-Server ~]# mysqladmin  --port=3306 -uroot -p flush-host

Enter password:

 

那么host cache是什么呢? 官方介绍如下:

 

The MySQL server maintains a host cache in memory that contains information about clients: IP address, host name, and error information. The server uses this cache for nonlocal TCP connections. It does not use the cache for TCP connections established using a loopback interface address (127.0.0.1 or ::1), or for connections established using a Unix socket file, named pipe, or shared memory.

 

 

简单来说,就是MySQL服务器在内存中维护一个包含客户端信息的缓存:IP地址,主机名和错误信息等。 服务器会将非本地TCP连接信息缓存起来。它不会缓存使用环回接口地址(127.0.0.1或者:: 1)建立的TCP连接,或者使用Unix套接字文件,命名管道或共享内存建立的连接。host cache信息可以通过performance_schema数据库下的host_cache表查询。

 

3:将变量host_cache_size设置为0

 

 

其实我想说这是一个最不靠谱的解决方法,只是让MySQL服务器不记录host cache信息而已。完全可以忽略这个方法。 

 

mysql> show variables like '%host_cache_size%';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| host_cache_size | 279   |
+-----------------+-------+
1 row in set (0.00 sec)
 
mysql> set global host_cache_size=0;
Query OK, 0 rows affected (0.00 sec)
 
mysql> select * from performance_schema.host_cache;
Empty set (0.00 sec)
 
mysql> 

 

 

 

知识点延伸

 

 

    关于参数max_connect_errors,不要误解其功能,这个不能作为防止穷举密码攻击的手段。如果您担心SYN泛滥攻击,max_connect_errors可能会在特定情况下帮助您。 MySQL 5.6中的PERFORMANCE_SCHEMA改进提供了有关潜在强力攻击的有意义的信息,但是只有在涉及主机缓存的情况下。关于这个可以参考博文Understanding max_connect_errors

 

 

 

参考资料:

 

http://mysqlblog.fivefarmers.com/2013/08/08/understanding-max_connect_errors/

https://dev.mysql.com/doc/refman/5.6/en/host-cache.html

https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_max_connect_errors

https://dev.mysql.com/doc/refman/5.7/en/blocked-host.html