Troubleshooting MySQL Admin Port Login Failures and Usage Best Practices

Background

MySQL 8.0.14 introduced the admin_port parameter to mitigate "too many connections" errors by providing a dedicated management port. However, users reported persistent connection failures even after configuring this feature. This article recreates the issue, analyzes root causes, and offers solutions.

Scenario Recreation

​Admin Port Configuration Parameters

create_admin_listener_thread = 1  # Enables a dedicated listener thread  
admin_address = localhost         # Bind address (IPv4/IPv6/hostname)  
admin_port = 33062                # Default port (customizable)  

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Steps to Reproduce

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Restart MySQL with the admin port enabled:

systemctl restart mysqld_3306
Verify connectivity via the admin port:

mysql -uroot -p -S /data/mysql/data/3306/mysqld.sock -P33062 -e 'SELECT VERSION()'
Simulate connection exhaustion:

SET GLOBAL max_connections = 1;  -- Limit connections to 1  
mysql -uroot -p -e 'SELECT VERSION()'  -- Triggers "ERROR 1040"

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Fault Analysis

​Key Observations​

• ​Socket vs. TCP Connections:
  Using localhost in admin_address binds the port to 127.0.0.1, while a Unix socket connection ignores the port setting entirely.
• ​Hostname Resolution Issues:
  If admin_address is set to localhost, MySQL resolves it to 127.0.0.1, which may not align with user privileges (e.g., accounts restricted to localhost).

Solution Steps

Bind to a Fixed IP Address:
Update admin_address to 127.0.0.1 in my.cnf:

admin_address = 127.0.0.1
Create a Dedicated Admin Account:
Grant privileges explicitly to the admin port:

CREATE USER 'admin'@'127.0.0.1' IDENTIFIED BY 'your_password';
GRANT ALL PRIVILEGES ON *.* TO 'admin'@'127.0.0.1' WITH GRANT OPTION;
FLUSH PRIVILEGES;

mysql -uadmin -p -h127.0.0.1 -P33062 -e 'SELECT VERSION()'

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Optimization Recommendations

• ​Least Privilege Principle: Restrict SUPER or SERVICE_CONNECTION_ADMIN privileges to essential accounts.
• ​Connection Pooling: Configure application data sources with initialSize and maxActive limits to control concurrency.
• ​SQL Performance Tuning: Optimize slow queries to reduce connection spikes.

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