我的本地主机上有mysql，可以使用root登录：

[root@pocnnr1n1 etc]# mysql -u root -p
Enter password:
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 8
Server version: 5.5.52-MariaDB MariaDB Server

Copyright (c) 2000, 2016, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+

现在，我在这个主机上有一个docker，它的ip地址是'172.17.0.2'
从docker ping到主机没有问题：

root@eaa90c1059f2:/app/airflow/dags# ping 192.168.211.251
PING 192.168.211.251 (192.168.211.251): 56 data bytes
64 bytes from 192.168.211.251: icmp_seq=0 ttl=64 time=0.208 ms

在docker中，如果我手动运行pymysql来创建连接：

conn= pymysql.connect(host='192.168.211.251', port=3306, user='root',
passwd='root', db='airflow')

我有以下错误：
pymysql.err.operationalerror:（1045，“拒绝访问用户'root'@'172.17.0.2'（使用密码：yes）”）
如果我将ip地址更改为“172.17.0.2”，如下所示：

conn= pymysql.connect(host='172.17.0.2', port=3306, user='root',
passwd='root', db='airflow')
I have the following error:

pymysql.err.operationalerror:（2003，“无法连接到'172.17.0.2'上的mysql服务器（[errno 111]连接被拒绝）”）
更新：my.cnf如下：

[mysqld]
transaction-isolation = READ-COMMITTED

# Disabling symbolic-links is recommended to prevent assorted security risks;

# to do so, uncomment this line:

# symbolic-links = 0

key_buffer = 16M
key_buffer_size = 32M
max_allowed_packet = 32M
thread_stack = 256K
thread_cache_size = 64
query_cache_limit = 8M
query_cache_size = 64M
query_cache_type = 1

max_connections = 550

# expire_logs_days = 10

# max_binlog_size = 100M

# log_bin should be on a disk with enough free space. Replace '/var/lib/mysql/mysql_binary_log' with an appropriate path for your system

# and chown the specified folder to the mysql user.

log_bin=/var/lib/mysql/mysql_binary_log

# explicit_defaults_for_timestamp = 1

binlog_format = mixed

read_buffer_size = 2M
read_rnd_buffer_size = 16M
sort_buffer_size = 8M
join_buffer_size = 8M

# InnoDB settings

innodb_file_per_table = 1
innodb_flush_log_at_trx_commit  = 2
innodb_log_buffer_size = 64M
innodb_buffer_pool_size = 4G
innodb_thread_concurrency = 8
innodb_flush_method = O_DIRECT
innodb_log_file_size = 512M

[mysqld_safe]
log-error=/var/log/mariadb/mariadb.log
pid-file=/var/run/mariadb/mariadb.pid