Hi Guys,
Those of you using Plesk with Blesta or other billing system on the same box would have encountered issues with empty responses, page disconnects/timeouts due to the fact that Plesk restarts Apache on every change and hence the process never completes gracefully on Blesta.
One of the workaround was to increase the "Apache restart interval" in "Apache Web Server Settings" on the Plesk Control Panel to a reasonable duration to avoid restarting everytime a change was made. Although this does improve on things, it still would cause issues if there were requests exactly at the time of restarts.
The solution to this issue is to set Plesk to restart Apache gracefully or in other terms reload Apache, not restart. Here is how to do this given on the plesk knowledgebase:
https://kb.plesk.com/en/112020
The above solution has been tested by a user having Plesk & Hostbill billing system on the same box. Multiple simultaneous requests were made and all of them completed smoothly & without any issues on either ends.
Note: It is recommended to do a Apache configtest and clearing up issues before setting up graceful restarts:
>apachectl configtest
Hope this helps others.
Thanks.