kubectl basics

kubectl has sub-commands (or plugins) which have their own syntax.

kubectl get NAME|SHORTHAND|KIND (all)

Meet the most iconic and built-in command: get

kubectl get

fails with

You must specify the type of resource to get. Use "kubectl api-resources" for a complete list of supported resources.
...

Great! Now we get to use another sub-command

kubectl api-resources

NAME               SHORTNAMES  APIVERSION  NAMESPACED   KIND
bindings                       v1          true         Binding
componentstatuses  cs          v1          false        ComponentStatus
configmaps         cm          v1          true         ConfigMap
endpoints          ep          v1          true         Endpoints
events             ev          v1          true         Event
limitranges        limits      v1          true         LimitRange
namespaces         ns          v1          false        Namespace
nodes              no          v1          false        Node
...

we can use NAME, SHORTNAME or KIND to get individual items

Nodes (NAME) is something we have now

kubectl get nodes

NAME                                            STATUS   ROLES                                 AGE   VERSION
ip-192-168-21-119.eu-north-1.compute.internal   Ready    cluster-2-16-2022-12-11-18-29-59      15m   v1.24.7-eks-fb459a0
ip-192-168-37-163.eu-north-1.compute.internal   Ready    bot-64-128-2022-12-11-19-32-56        73m   v1.24.7-eks-fb459a0
ip-192-168-45-164.eu-north-1.compute.internal   Ready    prometheus-2-16-2022-12-11-18-29-59   18h   v1.24.7-eks-fb459a0
...

or with shortname (SHORTNAMES)

kubectl get no

or with "singular" (KIND)

kubectl get node

What are all these fields?

$ kubectl get nodes
  NAME  STATUS  ROLES  AGE  VERSION
  ...

NAME is the name
STATUS is the current Status
ROLES node roles (more later)
AGE tells us when the node joined the cluster (not uptime of the machine)
VERSION is the version of the nodes kubelet (more later) - it's not version of the kubernetes master or API.

Kubernetes version upgrade is usually done like this:

First the kubernetes master is upgraded
Then nodes are upgraded one by one

Therefore versions of nodes can differ.

Master is now called Control-Plane https://github.com/kubernetes/website/issues/6525

kubectl get KIND NAME (one)

kubectl get node ip-192-168-21-119.eu-north-1.compute.internal

NAME                                            STATUS   ROLES                              AGE   VERSION
ip-192-168-21-119.eu-north-1.compute.internal   Ready    cluster-2-16-2022-12-11-18-29-59   38m   v1.24.7-eks-fb459a0

Output formatting

cut + awk + blerp!

$ kubectl get node | cut -f1 -d' '
  NAME
  ip-192-168-21-119.eu-north-1.compute.internal
  ip-192-168-37-163.eu-north-1.compute.internal
  ip-192-168-45-164.eu-north-1.compute.internal
  ...

--no-headers

$ kubectl get node --no-headers | cut -f1 -d' '
  ip-192-168-21-119.eu-north-1.compute.internal
  ip-192-168-37-163.eu-north-1.compute.internal
  ...

Position is free

$ kubectl get --no-headers node | cut -f1 -d' '
  ip-192-168-21-119.eu-north-1.compute.internal
  ip-192-168-37-163.eu-north-1.compute.internal
  ...

As long as it's not before command (plugin) name:

$ kubectl --no-headers get node
  Error: flags cannot be placed before plugin name: --no-headers

--help is your friend

kubectl get --help

Tells us that there are other formatting options

  ...
  [(-o|--output=)json|yaml|name|go-template|go-template-file|template|templatefile|jsonpath|jsonpath-as-json|jsonpath-file|custom-columns|custom-columns-file|wide]
  ...

kubectl get node -o name

node/ip-192-168-16-105.eu-north-1.compute.internal
node/ip-192-168-17-241.eu-north-1.compute.internal
...

kubectl get node -o wide

kubectl get node -o yaml

kubectl get node -o custom-columns=nimi:.metadata.name,lankoja:.status.capacity.cpu,rammia:.status.capacity.memory

kubectl get node -o json

kubectl describe

kubernetes is standard until it is not

Kinds / API resources depends on kubernetes version and flavor

$ kubectl api-resources -o name
  endpoints
  endpointslices.discovery.k8s.io

  eniconfigs.crd.k8s.amazonaws.com  <--- AWS flavor

  events
  events.events.k8s.io
  flowschemas.flowcontrol.apiserver.k8s.io
  ...

You have reached the end of this section! Continue to the next section:

4. Namespace