Hosting public DNS on UDP/53

Questions / Help
1

I am not able to get UDP port 53 to work.
I am trying to set up a dnsdist DNS server facing public internet - my dnsdist.conf has
setLocal(“0.0.0.0”)

My Dockerfile has
EXPOSE 53/udp 53/tcp

My fly.toml
[[services]]
internal_port = 53
protocol = “udp”

[[services.ports]]
port = 53
handlers =
force_https = false

[[services]]
internal_port = 53
protocol = “tcp”

[[services.ports]]
port = 53
handlers =

I have configured a public static ipv4 (x.x.x.x)

tcp works fine:
$ dig @x.x.x.x -p 53 google.com +tcp
google.com. 300 IN A 142.250.102.100

but UDP times out
$ dig @x.x.x.x -p 53 google.com
;; communications error to x.x.x.x#53: timed out

What am I doing wrong?

2

UDP services require your app to bind on exactly the address fly-global-services. This is in fact an entry in /etc/hosts that resolves to a special “udp service” address for each machine. Because this may change, apps should always use the fly-global-services alias. However, the TCP side of your app should bind to 0.0.0.0 and NOT fly-global-services.

3

Do you mean I shoud look up the IP in /etc/host and at startup update the dnsdist.conf to use that IP?

Regarding it may change - do you mean it can change while the machine is running - or would checking at startup be safe?

Edit: I’m stuck with trying to configure dnsdist to separate tcp and udp - maybe to use fly.io we would need to move to another resolver

4

No, usually this should just work as an argument to bind() because it does the lookup internally.

Is it possible to maybe launch 2 different machines, one for TCP and one for UDP, using process groups? I know this is a massive hack and really not optimal, but it might be what you’ll need to get this working for now. We’re looking into improvements to how UDP services are implemented soon.

5

This topic was automatically closed 7 days after the last reply. New replies are no longer allowed.