Anycast not applicable with UDP

Questions / Help
1

Hi there,

Recently I deployed gdnsd on fly and the experience was very good. But when testing with servers in different places, nyc and sin, I found that only the sin server responded quickly (sin is the primary region in fly.toml), while nyc was slow. I suspect this is due to udp not being applied anycast.

Also, the software is listening ipv6 but can’t get response by dig testdomain.invalid @ipv6_addr, only timeout. Is udp on ipv6 also not allowed, just like shared ipv4?

My fly.toml:

# fly.toml app configuration file generated for zzzprimarydns on 2024-06-25T03:08:35Z
#
# See https://fly.io/docs/reference/configuration/ for information about how to use this file.
#

app = 'dnstest'
primary_region = 'sin'

[build]

[[services]]
  internal_port = 53
  protocol = "udp"

  [[services.ports]]
    port = 53

[[vm]]
  size = 'shared-cpu-1x'
2

update: udp on ipv6 not possible now, see Running Fly Apps On UDP and TCP · Fly Docs. Hope this day comes earlier.

1 Like
3

I think this may differs from previous posts like https://community.fly.io/t/tcp-vs-udp-anycast-routing-inconsistency-at-fly-io or https://community.fly.io/t/udp-packet-routing-testing, their route was misdirected to multi-regions but for me it’s only sin, more like unicast than wrong anycast. :shushing_face:

4

Sorry it’s all my fault! Scale your app to multi region before asking the stupid “why anycast not applicable with udp” with only one machine in sin :sob:

1 Like
5

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