We have configures our stunnel properly in Ubuntu 16.04 , also it is starting properly we are getting our data in application which comes from stunnel server. Although I cannot find any proper way to stop stunnel. I tried killing the pid of stunnel , but killing pid is not a proper way to stop.
Thanks
Killing the PID sounds pretty bad, but it is the common way to stop processes in linux. "Kill" is just another name for "send signal". If you issue a kill $pid, then a SIGTERM is sent to that process.
The process can then handle the signal and perform a clean shutdown. This is also the way many programs implement a configuration reloading functionality, they often use SIGHUP for that (kill -SIGHUP $pid).
So, as long as you don't use kill -SIGKILL $pid (or in short: kill -9 $pid) the program can handle that signal and gracefully shutdown.
More about signals on linux: https://en.wikipedia.org/wiki/Signal_(IPC)#List_of_signals