Kind: How does "kubectl cluster-info" find or discover the cluster ...

[nmvega]

Hello Friends:

I have a question.

Given the information I compiled further below, how do either of the following two commands find anything at all?

nmvega@vps10$ kubectl cluster-info                       # --or--
nmvega@vps10$ kubectl cluster-info --context kind-kind

Kubernetes master is running at https://127.0.0.1:32773
KubeDNS is running at https://127.0.0.1:32773/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

Why I ask:

The API-Server port exposed to the outermost docker ("bare-metal") host is 32773 (see below), which is not a well-known port to the kubectl(1) command (at least not that I know of).

Similarly, the 172.17.0.0/16 address-space for the docker-hosted Kubernetes nodes aren't well-known to kubectl(1) either (again, not that I know of). And even if it was, kubectl(1) would need to somehow discover that 172.17.0.5 is the control-plane (API server).

I feel like I'm missing a concept or magic somewhere. :)

In any case, here is some information to help you help me. Thank you in advance!

Container information, including internal / external port mappings ...

CONTAINER ID  IMAGE                 NAMES               PORTS
c93b0d105ff8  kindest/node:v1.17.0  kind-control-plane  127.0.0.1:32773->6443/tcp
d61d797f8b58  kindest/node:v1.17.0  kind-worker1
f7ab13ae4aae  kindest/node:v1.17.0  kind-worker2
cfb036b2d1b0  kindest/node:v1.17.0  kind-worker3

And here are their pair-wise IP-Addresses ...

172.17.0.5
172.17.0.4
172.17.0.2
172.17.0.3

And the API-Server Port connections between them ...

nmvega@vps10$ docker container exec -it kind-worker ss | grep 6443
tcp ESTAB 0 0 172.17.0.4:33190 172.17.0.5:6443 
tcp ESTAB 0 0 172.17.0.4:33114 172.17.0.5:6443 

nmvega@vps10$ docker container exec -it kind-worker2 ss | grep 6443
tcp ESTAB 0 0 172.17.0.3:52560 172.17.0.5:6443 
tcp ESTAB 0 0 172.17.0.3:52588 172.17.0.5:6443 

nmvega@vps10$ docker container exec -it kind-worker3 ss | grep 6443
tcp ESTAB 0 0 172.17.0.2:56666 172.17.0.5:6443 
tcp ESTAB 0 0 172.17.0.2:56586 172.17.0.5:6443 

nmvega@vps10$ docker container exec -it kind-control-plane ss -l | grep 6443
tcp LISTEN 0 4096 *:6443  # This is: 172.17.0.5

And finally, LISTENed to ports and processes on the docker ("bare-metal") outer Host ...

nmvega@vps10$ sudo netstat -ntlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address      Foreign Address    State       PID/Program name    
tcp        0      0 127.0.0.1:32773    0.0.0.0:*          LISTEN      200358/docker-proxy 
tcp        0      0 0.0.0.0:5355       0.0.0.0:*          LISTEN      142/systemd-resolve 
tcp        0      0 127.0.0.53:53      0.0.0.0:*          LISTEN      142/systemd-resolve 
tcp        0      0 0.0.0.0:22         0.0.0.0:*          LISTEN      164/sshd            
tcp6       0      0 :::5355            :::*               LISTEN      142/systemd-resolve 
tcp6       0      0 :::22              :::*               LISTEN      164/sshd

[BenTheElder]

KIND uses the KUBECONFIG "standard" to write credentials. there is a file most likely in $HOME/.kube/config containing the cluster address, credentials, etc.

https://kubernetes.io/docs/concepts/configuration/organize-cluster-access-kubeconfig/

[nmvega]

KIND uses the KUBECONFIG "standard" to write credentials. there is a file most likely in $HOME/.kube/config containing the cluster address, credentials, etc.

https://kubernetes.io/docs/concepts/configuration/organize-cluster-access-kubeconfig/

Thank goodness it makes sense (no magic after all).

And here I was -- before writing my question -- searching as follows (yet didn't think to egrep(1) for kube, too; which is actually the right thing to search for):

nmvega@vps10$ cd ~; find . | grep -i kind # Sigh! LoL

Thank you so much!

[BenTheElder]

you're most welcome :-)

most kubernetes provisioning tools do something similar, we write to the kuebconfig file following some rules from kubectl about which file to use based on the --kubeconfig flag and KUBECONFIG environment variable and user HOME dir, we then set current-context to the one for this cluster.

you can also check just the kind part out with kind get kubeconfig and do this again for a running cluster with kind export kubeconfig

[BenTheElder]

the rules are at https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands#config

[nmvega]

Excellent! You guys probably had answered this already (or in the docs), but maybe this question and answer wording will help others searching in the future. (I guess that's my cop-out for not searching for kube). :) Ttys