Those are probably GC pauses. Memory tuning is probably needed. Check the parameters that you already have customised if they make sense.
Our nodes go down periodically, around 1-2 times each day. Downtime is from <1 second to 30 or so seconds.
INFO [GossipTasks:1] 2016-02-22 10:05:14,896 Gossiper.java (line 992) InetAddress /22.214.171.124
is now DOWN
INFO [RequestResponseStage:8844] 2016-02-22 10:05:38,331 Gossiper.java (line 978) InetAddress /126.96.36.199
is now UP
I find nothing odd in the logs around the same time. I logged a ping with timestamp and checked during the same time and saw nothing weird (ping is less than 2ms at all times).
Does anyone have any suggestions as to why this might happen?