DNS SRV instancer doesn't deal well with missing port number

[bboreham]

It appears the Kubernetes DNS server will return 0 in the port number slot under some circumstances (most of the ones I tried), and dnssrv/instancer.go turns this into :0 on the address.

Am I holding it wrong, or would you accept a PR to pass back the bare name if the port is 0?

[peterbourgon]

I find that strange; isn't an SRV record explicitly meant to contain a port? Can e.g. net.Dial possibly succeed without a one?

[bboreham]

Looks like if I name the port and look it up by name then I get the number; otherwise zero.

$ nslookup -type=SRV _http._tcp.distributor-h.cortex.svc.cluster.local. 10.244.218.156
Server:		10.244.218.156
Address:	10.244.218.156#53

_http._tcp.distributor-h.cortex.svc.cluster.local	service = 10 50 80 3630646565633364.distributor-h.cortex.svc.cluster.local.
_http._tcp.distributor-h.cortex.svc.cluster.local	service = 10 50 80 6563396264376365.distributor-h.cortex.svc.cluster.local.

$ nslookup -type=SRV distributor-h.cortex.svc.cluster.local. 10.244.218.156
Server:		10.244.218.156
Address:	10.244.218.156#53

distributor-h.cortex.svc.cluster.local	service = 10 50 0 3630646565633364.distributor-h.cortex.svc.cluster.local.
distributor-h.cortex.svc.cluster.local	service = 10 50 0 6563396264376365.distributor-h.cortex.svc.cluster.local.

service definition:

apiVersion: v1
kind: Service
metadata:
  name: distributor-h
  namespace: cortex
spec:
  clusterIP: None
  ports:
    - port: 80
      name: http
  selector:
    name: distributor

[bboreham]

And, in the case I want to work, I'm adding a port number before Dial() is called.

[peterbourgon]

Do you think Kubernetes assumes you'll always try to connect to port 80 by default? Or maybe that it can elide port 80 if it's the only defined port for the service? As a test, could you try to do this with a service that has only one non-80 port defined, and a service with two ports defined?

[peterbourgon]

To be clear, I'm happy to adjust the behavior for this situation however makes sense. I'm just trying to figure out what makes sense :)

[bboreham]

As a test, could you try to do this with a service that has only one non-80 port defined, and a service with two ports defined?

Always zero if I try the bare name,

[peterbourgon]

So like... does Kubernetes expect you to know the port, and if so how? Or does it do the port routing for you, assuming you connect to 80 by default or something?

[bboreham]

I haven't researched those questions, and am unlikely to get to it soon.
Since naming the port does work fine in my case, I amend my request to "go-kit should error if the port returned by DNS is zero", since the failure mode when you Dial :0 is hard to diagnose.

[bboreham]

While I'm here, do you know if anyone's done an Instancer via watch on Kubernetes Endpoints?

[peterbourgon]

Not to my knowledge.