Unexpected TCP latency results

[atward]

There's not much you can do about it, but thought I should raise it as an FYI for future users.

When running awsping TCP test I got the following results from Australia, which was really confusing until I realised there was a transparent proxy in place.

$ ./awsping -verbose 2 -repeats 3
      Code            Region                             Try #1          Try #2          Try #3     Avg Latency
    0 sa-east-1       South America (São Paulo)         5.94 ms         5.42 ms         5.21 ms         5.52 ms
    1 eu-west-1       Europe (Ireland)                  5.36 ms         6.09 ms         5.40 ms         5.62 ms
    2 us-east-2       US-East (Ohio)                    6.59 ms         5.50 ms         4.85 ms         5.65 ms
    3 ap-northeast-2  Asia Pacific (Seoul)              6.30 ms         5.27 ms         5.49 ms         5.69 ms
    4 ap-south-1      Asia Pacific (Mumbai)             6.44 ms         5.46 ms         5.16 ms         5.69 ms
    5 us-west-1       US-West (California)              7.09 ms         5.21 ms         4.94 ms         5.75 ms
    6 ap-southeast-1  Asia Pacific (Singapore)          6.25 ms         5.51 ms         5.93 ms         5.89 ms
    7 us-east-1       US-East (Virginia)                6.73 ms         5.33 ms         5.64 ms         5.90 ms
    8 us-west-2       US-West (Oregon)                  6.19 ms         5.91 ms         5.70 ms         5.94 ms
    9 eu-central-1    Europe (Frankfurt)                6.63 ms         6.05 ms         5.42 ms         6.03 ms
   10 ap-southeast-2  Asia Pacific (Sydney)             7.18 ms         5.77 ms         5.96 ms         6.31 ms
   11 ap-northeast-1  Asia Pacific (Tokyo)              8.49 ms         5.02 ms         5.43 ms         6.31 ms

Perhaps docs need to be updated to explain what the 'TCP' test does (3 way handshake RTT to http endpoint), or make HTTP the default.

[ekalinin]

Hi atward,

Thanks for report. But your result is very strange. Here's my try from aws ec2 instance (m4.2xlarge) from Sydney region:

$ ./awsping -verbose 2 -repeats 3
      Code            Region                             Try #1          Try #2          Try #3     Avg Latency
    0 ap-southeast-2  Asia Pacific (Sydney)             1.36 ms         1.77 ms         1.91 ms         1.68 ms
    1 ap-northeast-1  Asia Pacific (Tokyo)            105.13 ms       105.76 ms       105.77 ms       105.55 ms
    2 ap-northeast-2  Asia Pacific (Seoul)            132.96 ms       132.98 ms       132.93 ms       132.96 ms
    3 us-west-1       US-West (California)            158.34 ms       156.92 ms       157.56 ms       157.61 ms
    4 us-west-2       US-West (Oregon)                161.97 ms       162.12 ms       161.85 ms       161.98 ms
    5 ap-southeast-1  Asia Pacific (Singapore)        169.35 ms       169.38 ms       169.37 ms       169.37 ms
    6 us-east-2       US-East (Ohio)                  208.23 ms       208.37 ms       207.82 ms       208.14 ms
    7 ap-south-1      Asia Pacific (Mumbai)           227.87 ms       227.83 ms       227.86 ms       227.86 ms
    8 us-east-1       US-East (Virginia)              233.17 ms       233.65 ms       233.26 ms       233.36 ms
    9 eu-west-1       Europe (Ireland)                299.22 ms       302.40 ms       304.86 ms       302.16 ms
   10 eu-central-1    Europe (Frankfurt)              310.09 ms       317.30 ms       310.51 ms       312.64 ms
   11 sa-east-1       South America (São Paulo)       341.90 ms       342.00 ms       341.60 ms       341.83 ms

[atward]

You're missing the key point: the transparent proxy

To replicate install squid, then add firewall rule: iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 3128

TCP RTT would then report localhost->localhost, not the actual (HTTP request->response) RTT to the service.