We are experiencing a strange problem.
Everything with Elastic Search is fine but we get sudden deaths now and again.
This may happen once a week or once a month or twice a day.
During this time, I do not believe the index count or query count is unusual.

I've attached the graphs


You can see the current rate of indexing and searching is not abnormal.
However, if you look at the "rate of opened http connections", this rocketed at 10:20.
The "search thread pool queue by size by node" also rocketed to > 1000 at this time.
This caused all nodes to go offline and ES to become unresponsive.

Has anyone had this and do you know the cause of such issues?

Any help will be much appreciated,