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  • MySQL参数max_connect_errors分析释疑

     

    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_cacheG;
    *************************** 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_cacheG;
    *************************** 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

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  • 原文地址:https://www.cnblogs.com/kerrycode/p/8405862.html
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