Jira install successfully, available on domain but not able to configure db getting 503 in response

[Wajahat Gul]

I have installed jira in centos server HTTP port 8990
RMI port 8991

And setup virtualhost for jira and jira is accessible on domain but when I'm trying to configure it on external mysql database it's not configured also i get exception of 503 when i get setup debugger and in network tab there is status code 503 during POST event