I recently found some VMs of one OVS node( from 30+ nodes) went down and not able to start with this error :
Xend has probably crashed! Invalid or missing HTTP status code.
There are many reasons behind this. And if you try to restart xend , it will not start.
The first place to look for is :
This log will say where exactly the issue is.
In my case my / filesystem was running out of space because one log file consumed almost 8 GB . So I have to delete that file and now xend started successfully.