Thursday, 12 August 2021

Tinkering with Kubernetes via kubectl - some pearls of wisdom ( from other way smarter people )

 I filched these two gems from a much smarter person and am re-posting them here ...

The first relates to Pod labels which, to be honest, I've not paid too much attention.

The original context was to use kubectl to retrieve the IP address of Pods with a specific Label, using nginx as an example.

I've built upon these using Calico Node as an example ...

So I've got two Calico Node pods running inside my cluster: -

kube-system   calico-node-jd867                                1/1     Running   3          13d
kube-system   calico-node-kwj42                                1/1     Running   0          13d

If I describe each of those Pods, I can retrieve their Labels ...

kubectl describe pod calico-node-jd867 --namespace kube-system

Labels:               controller-revision-hash=74c54477d6

kubectl describe pod calico-node-kwj42 --namespace kube-system

Labels:               controller-revision-hash=74c54477d6

Armed with the Labels, I can query just for Pods using one of those Labels e.g.

kubectl get pods --all-namespaces --selector k8s-app=calico-node

kube-system   calico-node-jd867   1/1     Running   3          13d
kube-system   calico-node-kwj42   1/1     Running   0          13d

Building upon that, I can then get, from each Pod, its respective IP address: -

kubectl get pods --all-namespaces --selector k8s-app=calico-node --output jsonpath='{range .items[*]}{.status.podIP}{"\n"}{end}'

Pivoting away from Pods and Labels, we can similarly use kubectl and some JSON wrangling to retrieve the Taints from each Node in the cluster: -

kubectl get nodes -o jsonpath='{range $.items[*]} {} {.spec.taints[*].effect}{"\n"}{end}' NoSchedule 

which is rather shiny !

Again, definitely NIH, but reposting 'cos it's awesome

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