I am running an EC2 m4.xlarge instance with an 500GB Cold HDD EBS volume used as a cache for an image resizing service I am running (thumbor behind nginx reverse proxy).
Every now and then the image service seems to be overloaded and I can't figure out where the bottle neck is. CPU load and memory seem fine, there doesn't appear to be a great deal more traffic at the time. One thing that seems to correlate with the problem is that almost every day at a specific time there is a drop on the VolumeReadBytes and a jump in the VolumeReadOps for like half an hour. I don't have any cron jobs running, the server is dedicated to just serving resized images. I don't know what this could possibly be. Could this be the problem?
Any advice would be greatly appreciated.