Hello,
My apps are deployed in São Paulo, but I’m seeing latency from South America increase from ~20 ms to ~160 ms. Strangely, latency from North America is now lower than from South America.
Has Fly changed request routing recently that could explain this?
Thanks!
Hi - It sounds like clients in South America might indeed be being routed to a North American edge (and then back to your GRU-hosted machine! what a roundtrip!). Can you help us check if this is the case by doing a traceroute from a client location in South America?
mtr -bzo "LSD NABWV" -rw your-app.fly.dev
(remember to use a code block when pasting the mtr result here!)
Also for clarity, it’s likely we didn’t change anything, but routing over the public internet depends on a bunch of factors under control of a handful of network operators, it’s more likely that’s what changed in this case. But the mtr or traceroute will give us some idea of what’s going on 
I believe it is routed through the US.
Here’s the output of `mtr`
Start: 2025-11-26T12:50:01-0300
HOST: m.local Loss% Snt Drop Last Avg Best Wrst StDev
1. AS??? dsldevice.lan (192.168.1.1) 0.0% 10 0 6.5 7.0 4.6 13.3 2.8
2. AS7303 host180.181-88-172.telecom.net.ar (181.88.172.180) 0.0% 10 0 15.7 9.0 5.8 15.7 3.4
3. AS??? ??? 100.0 10 10 0.0 0.0 0.0 0.0 0.0
4. AS??? ??? 100.0 10 10 0.0 0.0 0.0 0.0 0.0
5. AS7303 host234.181-96-113.telecom.net.ar (181.96.113.234) 0.0% 10 0 27.2 13.0 6.3 32.0 9.4
6. AS7303 host181.181-96-120.telecom.net.ar (181.96.120.181) 40.0% 10 4 55.6 18.3 6.7 55.6 18.9
7. AS12956 213.140.39.116 0.0% 10 0 50.1 12.6 6.5 50.1 13.3
8. AS12956 176.52.255.29 0.0% 10 0 48.7 35.6 30.3 48.7 6.4
9. AS12956 94.142.98.131 0.0% 10 0 142.5 131.2 124.8 156.1 10.2
10. AS12956 213.140.43.206 70.0% 10 7 160.8 138.7 127.2 160.8 19.1
11. AS7922 be-206-pe12.nota.fl.ibone.comcast.net (96.87.11.177) 0.0% 10 0 154.3 132.5 125.0 154.3 10.1
12. AS7922 be-4311-pe11.ashburn.va.ibone.comcast.net (96.110.32.178) 0.0% 10 0 147.8 152.6 145.2 173.3 9.5
13. AS??? ??? 100.0 10 10 0.0 0.0 0.0 0.0 0.0
14. AS??? ??? 100.0 10 10 0.0 0.0 0.0 0.0 0.0
15. AS40509 ip-66-241-125-111.shared.customer.flyio.net (66.241.125.111) 0.0% 10 0 157.1 149.6 145.1 160.0 5.6
From a host in Brazil outside Fly I get something much more normal:
Loss% Snt Drop Last Avg Best Wrst StDev
1. AS??? 169.254.169.254 (169.254.169.254) 0.0% 10 0 0.2 0.2 0.2 0.4 0.0
2. AS??? 100.100.100.1 (100.100.100.1) 0.0% 10 0 0.4 0.4 0.4 0.5 0.0
3. AS??? 10.108.0.97 (10.108.0.97) 0.0% 10 0 29.6 10.7 0.6 37.1 12.4
4. AS??? 10.108.0.17 (10.108.0.17) 0.0% 10 0 0.8 0.6 0.4 0.9 0.2
5. AS??? as7195.saopaulo.sp.ix.br (187.16.217.238) 0.0% 10 0 0.9 1.0 0.9 1.1 0.1
6. AS7195 ae100.776.edge9.gru1.as7195.net (200.25.91.97) 0.0% 10 0 1.8 2.1 1.8 3.6 0.5
7. AS40509 ip-66-241-125-111.shared.customer.flyio.net (66.241.125.111) 0.0% 10 0 1.2 1.2 1.2 1.4 0.1
we did some tuning for this, can you check if things look better?
@PeterCxy oh yes! now we’re talking.
I’m seeing less than 40ms average latency now.
The nerd in me would love to know what was the issue.
Thanks!