Add support for domain name as advertise address

[simonklb]

Is there any reason not to allow an API server advertising a domain name rather than just an IP address?

This would be useful when you want to have multiple masters behind a loadbalancer and using the IP address is not suitable, for example in the case of AWS ELB.

Please correct me if I'm wrong here, but from what I can tell the bind address option seems to be the address which the API server is going to listen on while the advertise address is what it is telling other components to use for communication.

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[simonklb]

Looks like this is being solved, at least partially, by the introduction of ControlPlaneEndpoint. kubernetes/kubernetes#59288

Even more work is being done to support HA masters here: kubernetes/kubernetes#58261

And the progress is being tracked here: kubernetes/kubeadm#261

[SamDecrock]

Setting ControlPlaneEndpoint does not fix the issue of changing the IP address. If I change the IP address, the API-server will not start. Even when setting ControlPlaneEndpoint

[hi-usui]

Setting ControlPlaneEndpoint does not fix the issue of changing the IP address. If I change the IP address, the API-server will not start. Even when setting ControlPlaneEndpoint

I second this. It is mandatory for me to specify IP address in "advertiseAddress", and when I put a hostname resolved by DNS in controlPlaneEndpoint in kubeadm, it still fails if IP address changes. Anything we can do?

[furkanmustafa]

This is an insane requirement. Such a parameter should just accept a hostname as well.

My current workaround is;

• decide a bogus IP (127.33.22.11) to be used in all nodes, use this for advertising
• manage an ipvs entry locally, to virtually map that ip to the changing target IP

FAKE_IP=127.33.22.11
REAL_IPS_OR_HOSTNAMES="127.0.0.1 $(dig +short api2)"
ipvsadm -A -t $FAKE_IP:6443
for ip in $REAL_IPS; do
  ipvsadm -a -t $FAKE_IP:6443 -r $ip:6443 -m
done

kube-apiserver \
  --advertise-address ${FAKE_IP} \
  ...

[furkanmustafa]

Hmm 🤔

E1217 00:46:52.116565    5486 controller.go:227] unable to sync kubernetes service: Endpoints "kubernetes" is invalid: subsets[0].addresses[1].ip: Invalid value: "127.33.22.11": may not be in the loopback range (127.0.0.0/8, ::1/128)

.. better choose an IP address out of this range. the rule above doesn't say anything about multicast ranges.

[mogliang]

is it still true that apiserver advertise address must be IP? i'm curious that why it cannot be hostname? what difficulity will be face if use hostname?