Why are Google Cloud Compute Engine WAN speeds less than what Google has documented

google-cloud-platformgoogle-compute-engine

I have a google compute engine instance in us-central1-b running Centos 7 with 1vCPU and 3.75GB RAM.

According to the section "Egress throughput caps" on https://cloud.google.com/compute/docs/networks-and-firewalls my internet speed should be something somewhat close to 2Gb ("Each core is subject to a 2 Gbits/second (Gbps) cap for peak performance.").

I have installed speedtest-cli (pip install speedtest-cli) and performed many tests at different times of day. My max download has been 500Mb and max upload has been 72Mb.

I don't really expect to get 2Gb on this little VM, but I would expect it to be much closer to 1Gbps and a more synchronous connection.

Have I missed some documentation somewhere explaining the WAN speeds better? Am I not understanding the referenced documentation correctly? Is my system somehow misconfigured causing these really slow asynchronous speeds?

Thanks for any feedback.

Also, there is no other traffic on this system; it's just a test box.

Best Answer

As per the documentation, "All caps are meant as maximum possible performance between two VM instances in the same zone, both using internal IP addresses." I verified running two instances running Centos 7 with 1vCPU and 3.75GB RAM in same zone using the "iperf" [1][2] (sudo yum install iperf) and received 1.64 Gbps.

On the GCE VM machine (with iperf install) in the same zone, run the 
command:
iperf -s 

On egress test GCE VM machine (with iperf install) run the command 
iperf -c xx.xx.xx.xx     (where xx.xx.xx.xx is internal IP of the other VM- 
instance)

output:
[ID] Interval       Transfer     Bandwidth
[3]  0.0-10.0 sec  1.91 GBytes  1.64 Gbits/sec

I verified running instance with 4 vCPUs as well and received 7.67 Gbits/sec as bandwidth which is very close to 8 Gbps as defined in the documentation. I would suggest you to verify the same.

Moreover, as Google does not have any control over ISP network and other factors involved (eg: routing etc.) over internet traffic, Google cannot guarantee the egress throughput for the egress network traffic from a virtual machine over the ISP network.

[1] https://iperf.fr/

[2] https://www.linode.com/docs/networking/diagnostics/diagnosing-network-speed-with-iperf

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