无法使用 localhost 从 vps 连接到 MySQL 数据库

Question

I have two environments: my local machine Mac and linux on VPS. The problem is that I can not connect using localhost to my db from VPS. On my local machine everything works fine.

Local:

mysql -u root mydb -h 127.0.0.1 --password=password --port=2345 //OK
mysql -u root mydb -h 0.0.0.0 --password=password --port=2345   //OK
mysql -u root mydb -h localhost --password=password --port=2345 //OK

Even using public ip of VPS I'm able to connect to remote db from local machine.

VPS:

mysql -u root mydb -h 127.0.0.1 --password=password --port=2345 //OK
mysql -u root mydb -h 0.0.0.0 --password=password --port=2345   //OK
mysql -u root mydb -h localhost --password=password --port=2345 //KO <-

Error:

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

I used the following docker file to create my image.

DockerFile:

FROM mysql:8.0
COPY *.sql /docker-entrypoint-initdb.d/

docker-compose.yaml:

version: '3.7'
services:
  ls:
    image: ***/db-container:v6 # <-my image
    container_name: db-container
    restart: always
    environment:
      MYSQL_DATABASE: 'mydb'
      MYSQL_USER: 'user'
      MYSQL_PASSWORD: 'password'
      MYSQL_ROOT_PASSWORD: 'password'
    ports:
      # <Port exposed> : < MySQL Port running inside container>
      - '2345:3306'
    expose:
      # Opens port 3306 on the container
      - '3306'
    volumes:
      - db-container:/var/lib/mysql
volumes:
  db-container:

Query inside container:

mysql> SELECT host, user FROM mysql.user;
+-----------+------------------+
| host      | user             |
+-----------+------------------+
| %         | root             |
| %         | user             |
| localhost | mysql.infoschema |
| localhost | mysql.session    |
| localhost | mysql.sys        |
| localhost | root             |
+-----------+------------------+


mysql> SELECT * FROM performance_schema.host_cache; 
Empty set (0.02 sec)

Answer 1

"localhost" says to use a socket. But VPS probably allows only TCP/IP connections, not "socket".

Answer 2

I guess on local machine, you are not using docker. However, on vps, you are.

On you local, mysql is installed on the OS itself, hence, it has exposed its socket file at /var/run/mysqld/mysqld.sock. However, on VPS, the socket is inside docker.

The highlight here is the difference between localhost and 127.0.0.1 in reference to mysql. On unix based systems(including mac), localhost connects via socket, while 127.0.0.1 connects via TCP/IP.

Try adding following under docker-compose volumes section. See if it works then.

volumes:
    - /var/run/mysqld/mysqld.sock:/var/run/mysqld/mysqld.sock

Answer 3

There are many different root causes for a connection denied.

Since it is possible to execute queries inside the container, the best course of action is to inspect the performance_schema.host_cache table:

SELECT * FROM performance_schema.host_cache;

It should point more precisely at the problem.

Doc: https://dev.mysql.com/doc/mysql-perfschema-excerpt/8.0/en/host-cache-table.html