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Kubernetes context

dannypsnl profile image 林子篆 Originally published at dannypsnl.github.io on ・3 min read

Before you beginning

You should already install kubectl this command line tool. And knowing what is Kubernetes. Knowing why we need to separate the environment for the different member.

Config for demo

At first, we need to prepare a configuration that can help us learning operations of context. Now, create a file called config_demo.

$ touch config_demo

Next, copy these contents into config_demo.

apiVersion: v1
kind: Config

contexts:
- context:
    cluster: ""
    user: ""
  name: backend
- context:
    cluster: ""
    user: ""
  name: frontend

In our assuming, we have two kinds of developers, frontend & backend.

Now, type kubectl --kubeconfig config_demo config get-contextsOutput:

$ kubectl --kubeconfig config_demo config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
          backend
          frontend

See, we have two contexts now. Let’s get into the next step.

$ kubectl --kubeconfig config_demo config use-context backend
Switched to context "backend".

This command, obviously, change our context to backend now. But how do we checking this fact at other times? Here we go!

$ kubectl --kubeconfig config_demo config current-context
backend

Ok, now we already know some basic operations of kubectl config this command, let’s see the current content of your config file:

apiVersion: v1
clusters: []
contexts:
- context:
    cluster: ""
    user: ""
  name: backend
- context:
    cluster: ""
    user: ""
  name: frontend
current-context: backend
kind: Config
preferences: {}
users: []

We got some new thing into it, but basically, the most important part is current-context, so now you know how kubectl store this info, then you know how to create this by modifying the config directly.

Now, let’s add some users to this config.

apiVersion: v1
# ignore
users:
- name: frontend-developer
- name: backend-developer

Then add setting credentail for them

$ kubectl --kubeconfig config_demo config set-credentials backend-developer --username=danny --password=danny
User "backend-developer" set.
$ kubectl --kubeconfig config_demo config set-credentials frontend-developer --username=notme --password=notme
User "frontend-developer" set.

Now let’s see what’s different in the config

apiVersion: v1
# ignore
users:
- name: backend-developer
  user:
    password: danny
    username: danny
- name: frontend-developer
  user:
    password: notme
    username: notme

p.s. Here, we use the basic auth, I won’t suggest using this kind of auth in the real world and remember don’t use the same value about username and password! I ever heard teacher use 1234 as a password when creating an example, and the student use 1234 even at work because used to do that, do make it happened to you!

Let’s go to the usage part, we would set up the user of the context

$ kubectl --kubeconfig config_demo config set-context frontend --namespace frontend --user frontend-developer
Context "frontend" modified.
$ kubectl --kubeconfig config_demo config set-context backend --namespace backend --user backend-developer
Context "backend" modified.

Then see the change inside of the config

apiVersion: v1
# ignore
contexts:
- context:
    cluster: ""
    namespace: backend
    user: backend-developer
  name: backend
- context:
    cluster: ""
    namespace: frontend
    user: frontend-developer
  name: frontend

As you see, we didn’t have a cluster so we can’t do some operation, so now we would use the kubernetes for docker environment default cluster to do the following task. To do so, we have to add the cluster to the config

apiVersion: v1
# ignore
- context:
    cluster: docker-for-desktop-cluster
    namespace: backend
    user: backend-developer
  name: backend

And also do this for frontend, remember we didn’t create a cluster, so you have included ~/.kube/config on your computer to get docker-for-desktop-cluster

Once you do this, any operation on the cluster would require auth information, example:

$ KUBECONFIG=~/.kube/config:config_demo kubectl get pod
Error from server (Forbidden): pods is forbidden: User "system:anonymous" cannot list pods in the namespace "backend"

p.s. Just a small tip: po as pod as pods in the command line.

How to login the user is another part so I won’t spend time on it but I can provide some references so that you can learn from those documentations. https://kubernetes.io/docs/reference/access-authn-authz/authentication/

Practical

But what I said won’t actually use in your job, unless you’re kube-master or technical leader or somewhat anyway you have to operate these fundamental part in kubernetes. So here I would tell you how to use context correctly, that’s set up KUBECONFIG this environment variable!

In your .bashrc, .zshrc or anywhere, insert this:

export KUBECONFIG=$KUBECONFIG:config1:config2:config3

Where are configs from? Usually, are copying from your cloud platform, for example: Azure , GCP , AWS.

Anyway, this config already contains context information, so after you set up your KUBECONFIG, you can see a lot of context by kubectl config get-contexts, then what you need is just use them!

Thanks for reading, see you next time.

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dannypsnl profile

林子篆

@dannypsnl

I am a programming language theory lover; good at system software like Networking, OS.

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