Jon Simpson

Poor Network Performance with AWS NAT AMI

10 Apr 2015 — aws, ami

[Update: Amazon resolved this issue in the 2015.03.0 version of its NAT instance AMI. If you’re seeing it - relaunch the NAT instance with the newer AMI.]

With the Amazon 2014.09.1 NAT instance AMI and certain instance types, poor network performance can be observed on instances behind the NAT. To fix, disable scatter/gather on the network interface of the instance. On a t2.small instance this took network performance on hosts using the NAT from 250kB/s to over 1MB/s immediately.

As root/sudo:

ethtool -K eth0 sg off

This command needs to be in the boot scripts, as it doesn’t persist over reboots. H/T to Server Fault.