kubectl-in-action

kubectl In Action

Or: How to use your Kubernetes remote control

This is a talk at the Pre-FOSDEM warmup with Kubernetes at Brussels Kubernetes Meetup, on Friday 2018-02-02, with the accompanying slide deck available via Speaker Deck.

Kubernetes comes with kubectl, a CLI allowing you to interact with your cluster. It supports operations ranging from configuration to managing workloads and services to handle access control to administrative tasks such as node maintenance. In this talk you’ll learn everything you need to know getting the most out of kubectl (and beyond).

Setup
Contexts
Docs
Managing workloads
Services
Accessing the API
RBAC
Debugging
Tips and tricks
Tooling
Further reading & watching

Setup

I’m new to a cluster, so I have a look around.

What version am I on (client-side and server-side)?

$ kubectl version
$ kubectl version --short

Can I have a generic dump of ~/.kube/config?

$ kubectl config view

Contexts

I have multiple clusters, want to switch around.

What contexts are available?

$ kubectl config get-contexts

Switch to a certain context:

$ kubectl config use-context minikube

Create context somek and switch to it:

$ kubectl config set-context somek --user=cluster-admin --namespace=meh && \
  kubectl config use-context somek

Docs

I’m lost. I can’t remember a command. I need examples.

What can I do with a command?

$ kubectl run -h
$ kubectl create -h | less

Got some usage examples?

$ kubectl run -h | tail -n+$(kubectl run -h | grep -n Example | grep -Eo '^[^:]+') | head -n $(kubectl run -h | grep -n Options | grep -Eo '^[^:]+')

What was that field in the manifest again?

$ kubectl explain statefulset.spec.template.spec

Managing workloads

What’s running?

I want to get an overview of all pods across all namespaces:

$ kubectl get pods --all-namespaces

I want to launch stuff.

Launching a simple jump pod:

$ kubectl run -i -t --rm jumpod --restart=Never --image=quay.io/mhausenblas/jump:0.2 -- sh

Do a dry-run for a long-running process (NGINX):

$ kubectl run webserver --image=nginx:1.13 --output=yaml --dry-run

Get the name of deployment labelled with run as key:

$ kubectl get deploy -l=run -o=custom-columns=:metadata.name --no-headers

Get the name of pod(s) labelled with run=webserver:

$ kubectl get po -l=run=webserver -o=custom-columns=:metadata.name --no-headers

Scale the webserver deployment to 2 replicas and observe the scaling:

# in shell terminal 1:
$ kubectl get po -l=run=webserver -o=custom-columns=:metadata.name --no-headers --watch

# in shell terminal 2:
$ kubectl scale deploy/webserver --replicas=2

Get rid of webserver deployment by scaling down to 0 and deleting it:

$ kubectl scale deploy/webserver --replicas=0
$ kubectl delete deploy/webserver

Services

I want to access stuff via the network.

Create a service webserver for a deployment and check it:

$ kubectl run webserver --image=nginx:1.13
$ kubectl expose deployment webserver --port=80 --target-port=80
$ kubectl describe svc -l=run=webserver

I’d like to curl the new webserver service from within the cluster:

$ kubectl run -i -t --rm curlpod --restart=Never --image=quay.io/mhausenblas/jump:0.2 -- curl webserver

Accessing the API

I need access to the Kubernetes API for development and testing.

$ kubectl proxy

RBAC

I want to use fine-grained access control.

So, can I have a namespace called test please?

$ kubectl create -f https://raw.githubusercontent.com/mhausenblas/kbe/master/specs/ns/ns.yaml

Let’s first create a service account dummy in the test namespace:

$ kubectl create serviceaccount dummy --namespace=test
$ kubectl get sa -n=test

Next, creating a role podreader in test namespace:

$ kubectl create role podreader --verb=get --verb=list --resource=pods --namespace=test
$ kubectl get roles --namespace=test

And now, I’ll use a rolebinding (in namespace test ) that connects all above, effectively stating the following: the service account dummy is only allowed to list and get pods (aka a podreader).

To verify, let’s first just have a look at the YAML manifest that represents this access control statement (using --dry-run=true) and only then actually create the binding:

$ kubectl create rolebinding podreaderbinding --role=podreader --serviceaccount=test:dummy --namespace=test --dry-run=true -o=yaml
$ kubectl create rolebinding podreaderbinding --role=podreader --serviceaccount=test:dummy --namespace=test

Now, checking, can the service account dummy list pods?

$ kubectl auth can-i list pods --as=system:serviceaccount:test:dummy --namespace=test

And what about, say, creating services?

$ kubectl auth can-i create services --as=system:serviceaccount:test:dummy --namespace=test

Debugging

I’m in deep trouble. I need to figure out why things went sideways.

Drink from the events firehose:

$ kubectl get events

Streaming the logs of a pod:

$ kubectl logs --follow $(kubectl get po -l=run=webserver -o=custom-columns=:metadata.name --no-headers)

Note of a problem and retrieve it:

$ kubectl annotate pods $(kubectl get po -l=run=webserver -o=custom-columns=:metadata.name --no-headers) troubleshoot='something really fishy going on here'
$ kubectl describe po $(kubectl get po -l=run=webserver -o=custom-columns=:metadata.name --no-headers) | grep troubleshoot

Get the content of a HTTP service running in the cluster to my local machine on port 8080:

$ kubectl port-forward $(kubectl get po -l=run=webserver -o=custom-columns=:metadata.name --no-headers) 8080:80

How’s one of my nodes doing? Note: requires Heapster installed.

$ kubectl top node minikube

Tips and tricks

I’m sold, kubectl is awesome! What else have you got?

Install and use auto-complete
Set KUBE_EDITOR to your favorite editor.
Maybe check out at the tooling section below and try one or more of the available extensions of kubectl?
Have a look at your history (see also my example).
Use kubed-sh with debug mode on.

Tooling

Gimme some more tools I can use to make my kubectl even cooler.

Extend and enhance kubectl with:

Source: Ahmet Alp Balkan on Twitter 01/2018.