'Can't create thread to handle new connection' on RDS I have two production instance of MySQL on AWS RDS that failed with:

2017-06-20T15:48:35.226833Z 0 [ERROR] Error log throttle: 1 'Can't create thread to handle new connection' error(s) suppressed
2017-06-20T15:48:35.226873Z 0 [ERROR] Can't create thread to handle new connection(errno= 11)


These are two db.m4.2xlarge instances and one capped at 102 connections while the other capped at 38. Not more connections could be made past that. This type of instance should be able to accept more than 2K connections with the default config (which I have).

I opened a support ticket and they manually changed some settings on the instances. After that and a reboot, I could connect with 2500 connections on each server to validate resolution.

Any idea why they had to manually change some settings on the instance (underlying OS I guess)? Is this something to be expected from RDS? What could we be doing that triggered this condition?

Thanks!
This might help you 
A Percona blog of tale of 2 limits

We (not RDS) had the second issue after we failed over as part of a disaster recovery exercise.

How old are the RDS instances, were they upgraded, replaced failed over...? Enjoy :)