Cause: mysql has a max_connection variable where connections to mysql cannot exceed the value of the variable.
Solution: increase the value of the max_connection variable
1. Check max_connections configured
mysql
MariaDB [(none)]> show variables like "%connection%";
+---------------------------+--------------------+
| Variable_name | Value | +---------------------------+--------------------+ | character_set_connection | utf8mb4 |
| collation_connection | utf8mb4_general_ci | | default_master_connection | |
| extra_max_connections | 1 |
| max_connections | 151 |
| max_user_connections | 0 |
+---------------------------+--------------------+
2. Check max used connections and connection error:
MariaDB [(none)]> show global status like "%connections%"; +-----------------------------------+-------+
| Variable_name | Value |
+-----------------------------------+-------+
| Connection_errors_max_connections | 64 | | Connections | 6613 |
| Max_used_connections | 152 |
| Slave_connections | 0 |
| wsrep_open_connections | 0 | +-----------------------------------+-------+
3. Increase max connection
MariaDB [(none)]> SET GLOBAL max_connections=4096;
Query OK, 0 rows affected (0.000 sec)
4. Check again
MariaDB [(none)]> show variables like "%connection%";
+---------------------------+--------------------+ | Variable_name | Value | +---------------------------+--------------------+
| character_set_connection | utf8mb4 | | collation_connection | utf8mb4_general_ci |
| default_master_connection | |
| extra_max_connections | 1 |
| max_connections | 4096 |
| max_user_connections | 0 |
+---------------------------+--------------------+