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We are installing the application in the servers, but it doesn't work when App/Stage Servers connect to DB Server, could you help setup the firewall for the traffic between them? The connection information is as follows.
192.168.110.16(App2) to 192.168.100.21(DB) via 3306
192.168.110.17(App3) to 192.168.100.21(DB) via 3306
192.168.100.18(Stage) to 192.168.100.21(DB) via 3306
Please restart your device and recheck all the connection settings. I think after doing it your problem will be solved.