Is EC2 bandwidth full duplex?

Question

Amazon documents the network speed of each instance type, giving it a rating like "25 Gbps". As long as certain restrictions are avoided, one can largely expect to achieve this bandwidth between hosts in the same region.

My question is, is this bandwidth full-duplex? Can I get 25 Gbps in both directions between two hosts documented as having 25 Gbps network limits?

Answer 1

If you place instances in a cluster placement group, the traffic is full duplex. From docs:

Inter instance traffic within the same region can utilize up to 5 Gbps for single-flow and up to 100 Gbps for multi-flow traffic in each direction (full duplex).

Network traffic to the Internet is limited to 5 Gbps (full duplex).

If the instances are not in a cluster, then the AWS docs do not specify if network traffic is full duplex or not. Thus, one can assume its not in that case.

Answer 2

There is nothing to indicate this is not full-duplex. in the aws doc page , assuming you do not exceed the limits for the VM cpu type, or number of connections etc.

Timing from a one way copy

time scp WINDOWS.X64_213000_db_home.zip ubuntu@ip-172-31-28-80:~
WINDOWS.X64_213000_db_home.zip

100% 1376MB 101.2MB/s   00:13    

real    0m13.809s
user    0m3.210s
sys 0m2.786s

timing from simultaneous copy of the same file - to each other VM

time scp WINDOWS.X64_213000_db_home.zip ubuntu@ip-172-31-28-80:/tmp
WINDOWS.X64_213000_db_home.zip                                                                                                                    100% 1376MB  91.0MB/s   00:15    

real    0m15.675s
user    0m3.376s
sys 0m2.969s

time scp WINDOWS.X64_213000_db_home.zip ubuntu@ip-172-31-24-217:/tmp
WINDOWS.X64_213000_db_home.zip                                                                                                                                              100% 1376MB  98.3MB/s   00:13    

real    0m14.242s
user    0m3.381s
sys 0m3.134s

Thus both way, simultaneous copy speed is very close to one way copy speed. Both were t2.medium machine - which is rated to be "upto 1 GBps" from here but for such a small 1.4 GB file it did not get a time to peak bandwidth usage. Hope this helps