Description:
When using the telnet command to check MySQL Router's liveness, the Router will block the client after a specific number of connection attempts.
Root Cause:
Router likely increments a max_connect_errors counter for each failed/unfinished connection (common with telnet). Upon hitting the threshold, it invokes system firewall tools to add blocking rules. This approach is overly aggressive and inappropriate for application-layer issues.
Expected Behavior:
Low-frequency health checks should not trigger IP isolation.
How to repeat:
Steps to Reproduce (I set max_connect_errors to 10 to quick reproduce it):
1. Start a MySQL Router instance on a server (Server_A). The routing config is like this:
[routing:30000]
bind_address = 0.0.0.0
bind_port = 30000
destinations = 9.135.59.11:3306
routing_strategy = first-available
max_connect_errors = 10
2. telnet <Router_IP> 30000 . And quit the connection.
3. check log. We can find log below:
2025-07-01 14:54:36 routing INFO [7fb2aeffd700] [routing:30000] incrementing error counter for host of 9.134.224.84:41118 (now 1)
2025-07-01 14:54:37 routing INFO [7fb2e71db700] [routing:30000] incrementing error counter for host of 9.134.224.84:41154 (now 2)
2025-07-01 14:54:38 routing INFO [7fb2e69da700] [routing:30000] incrementing error counter for host of 9.134.224.84:41174 (now 3)
2025-07-01 14:54:39 routing INFO [7fb2e61b8700] [routing:30000] incrementing error counter for host of 9.134.224.84:41200 (now 4)
2025-07-01 14:54:40 routing INFO [7fb2e59b7700] [routing:30000] incrementing error counter for host of 9.134.224.84:41224 (now 5)
2025-07-01 14:54:41 routing INFO [7fb2e51b6700] [routing:30000] incrementing error counter for host of 9.134.224.84:41246 (now 6)
2025-07-01 14:54:42 routing INFO [7fb2e4994700] [routing:30000] incrementing error counter for host of 9.134.224.84:41276 (now 7)
2025-07-01 14:54:43 routing INFO [7fb2d3fff700] [routing:30000] incrementing error counter for host of 9.134.224.84:41312 (now 8)
2025-07-01 14:54:44 routing INFO [7fb2d37fe700] [routing:30000] incrementing error counter for host of 9.134.224.84:41326 (now 9)
2025-07-01 14:54:45 routing WARNING [7fb2d2ffd700] [routing:30000] blocking client host for 9.134.224.84:41348
Suggested fix:
Provide a config to close this rule.
Description: When using the telnet command to check MySQL Router's liveness, the Router will block the client after a specific number of connection attempts. Root Cause: Router likely increments a max_connect_errors counter for each failed/unfinished connection (common with telnet). Upon hitting the threshold, it invokes system firewall tools to add blocking rules. This approach is overly aggressive and inappropriate for application-layer issues. Expected Behavior: Low-frequency health checks should not trigger IP isolation. How to repeat: Steps to Reproduce (I set max_connect_errors to 10 to quick reproduce it): 1. Start a MySQL Router instance on a server (Server_A). The routing config is like this: [routing:30000] bind_address = 0.0.0.0 bind_port = 30000 destinations = 9.135.59.11:3306 routing_strategy = first-available max_connect_errors = 10 2. telnet <Router_IP> 30000 . And quit the connection. 3. check log. We can find log below: 2025-07-01 14:54:36 routing INFO [7fb2aeffd700] [routing:30000] incrementing error counter for host of 9.134.224.84:41118 (now 1) 2025-07-01 14:54:37 routing INFO [7fb2e71db700] [routing:30000] incrementing error counter for host of 9.134.224.84:41154 (now 2) 2025-07-01 14:54:38 routing INFO [7fb2e69da700] [routing:30000] incrementing error counter for host of 9.134.224.84:41174 (now 3) 2025-07-01 14:54:39 routing INFO [7fb2e61b8700] [routing:30000] incrementing error counter for host of 9.134.224.84:41200 (now 4) 2025-07-01 14:54:40 routing INFO [7fb2e59b7700] [routing:30000] incrementing error counter for host of 9.134.224.84:41224 (now 5) 2025-07-01 14:54:41 routing INFO [7fb2e51b6700] [routing:30000] incrementing error counter for host of 9.134.224.84:41246 (now 6) 2025-07-01 14:54:42 routing INFO [7fb2e4994700] [routing:30000] incrementing error counter for host of 9.134.224.84:41276 (now 7) 2025-07-01 14:54:43 routing INFO [7fb2d3fff700] [routing:30000] incrementing error counter for host of 9.134.224.84:41312 (now 8) 2025-07-01 14:54:44 routing INFO [7fb2d37fe700] [routing:30000] incrementing error counter for host of 9.134.224.84:41326 (now 9) 2025-07-01 14:54:45 routing WARNING [7fb2d2ffd700] [routing:30000] blocking client host for 9.134.224.84:41348 Suggested fix: Provide a config to close this rule.