7.1.12.2 Administrative Connection Management

As mentioned in Connection Volume Management, to allow for the need to perform administrative operations even when max_connections connections are already established on the interfaces used for ordinary connections, the MySQL server permits a single administrative connection to users who have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege).

Additionally, as of MySQL 8.0.14, the server permits dedicating a TCP/IP port for administrative connections, as described in the following sections.

Administrative Interface Characteristics

The administrative connection interface has these characteristics:

The server enables the interface only if the admin_address system variable is set at startup to indicate the IP address for it. If admin_address is not set, the server maintains no administrative interface.
The admin_port system variable specifies the interface TCP/IP port number (default 33062).
There is no limit on the number of administrative connections, but connections are permitted only for users who have the SERVICE_CONNECTION_ADMIN privilege.
The create_admin_listener_thread system variable enables DBAs to choose at startup whether the administrative interface has its own separate thread. The default is OFF; that is, the manager thread for ordinary connections on the main interface also handles connections for the administrative interface.

These lines in the server my.cnf file enable the administrative interface on the loopback interface and configure it to use port number 33064 (that is, a port different from the default):

[mysqld]
admin_address=127.0.0.1
admin_port=33064

MySQL client programs connect to either the main or administrative interface by specifying appropriate connection parameters. If the server running on the local host is using the default TCP/IP port numbers of 3306 and 33062 for the main and administrative interfaces, these commands connect to those interfaces:

mysql --protocol=TCP --port=3306
mysql --protocol=TCP --port=33062

Administrative Interface Support for Encrypted Connections

Prior to MySQL 8.0.21, the administrative interface supports encrypted connections using the connection-encryption configuration that applies to the main interface. As of MySQL 8.0.21, the administrative interface has its own configuration parameters for encrypted connections. These correspond to the main interface parameters but enable independent configuration of encrypted connections for the administrative interface:

The admin_tls_xxx and admin_ssl_xxx system variables are like the tls_xxx and ssl_xxx system variables, but they configure the TLS context for the administrative interface rather than the main interface.
The --admin-ssl option is like the --ssl option, but it enables or disables support for encrypted connections on the administrative interface rather than the main interface.
Because support for encrypted connections is enabled by default, it is normally unnecessary to specify --admin-ssl. As of MySQL 8.0.26, --admin-ssl is deprecated and subject to removal in a future MySQL version.

For general information about configuring connection-encryption support, see Section 8.3.1, “Configuring MySQL to Use Encrypted Connections”, and Section 8.3.2, “Encrypted Connection TLS Protocols and Ciphers”. That discussion is written for the main connection interface, but the parameter names are similar for the administrative connection interface. Use that discussion together with the following remarks, which provide information specific to the administrative interface.

TLS configuration for the administrative interface follows these rules:

If --admin-ssl is enabled (the default), the administrative interface supports encrypted connections. For connections on the interface, the applicable TLS context depends on whether any nondefault administrative TLS parameter is configured:
- If all administrative TLS parameters have their default values, the administrative interface uses the same TLS context as the main interface.
- If any administrative TLS parameter has a nondefault value, the administrative interface uses the TLS context defined by its own parameters. (This is the case if any admin_tls_xxx or admin_ssl_xxx system variable is set to a value different from its default.) If a valid TLS context cannot be created from those parameters, the administrative interface falls back to the main interface TLS context.
If --admin-ssl is disabled (for example, by specifying --admin-ssl=OFF, encrypted connections to the administrative interface are disabled. This is true even if administrative TLS parameters have nondefault values because disabling --admin-ssl takes precedence.
It is also possible to disable encrypted connections on the administrative interface without specifying --admin-ssl in negated form. Set the admin_tls_version system variable to the empty value to indicate that no TLS versions are supported. For example, these lines in the server my.cnf file disable encrypted connections on the administrative interface:
```
[mysqld]
admin_tls_version=''
```

Examples:

This configuration in the server my.cnf file enables the administrative interface, but does not set any of the TLS parameters specific to that interface:
```
[mysqld]
admin_address=127.0.0.1
```
As a result, the administrative interface supports encrypted connections (because encryption is supported by default when the administrative interface is enabled), and uses the main interface TLS context. When clients connect to the administrative interface, they should use the same certificate and key files as for ordinary connections on the main interface. For example (enter the command on a single line):
```
mysql --protocol=TCP --port=33062
      --ssl-ca=ca.pem
      --ssl-cert=client-cert.pem
      --ssl-key=client-key.pem
```
This server configuration enables the administrative interface and sets the TLS certificate and key file parameters specific to that interface:
```
[mysqld]
admin_address=127.0.0.1
admin_ssl_ca=admin-ca.pem
admin_ssl_cert=admin-server-cert.pem
admin_ssl_key=admin-server-key.pem
```
As a result, the administrative interface supports encrypted connections using its own TLS context. When clients connect to the administrative interface, they should use certificate and key files specific to that interface. For example (enter the command on a single line):
```
mysql --protocol=TCP --port=33062
      --ssl-ca=admin-ca.pem
      --ssl-cert=admin-client-cert.pem
      --ssl-key=admin-client-key.pem
```