Kubernetes series (Part 3): Use kubectl

Remember, kubectl contacts with apis of nodes and controls the nodes. The way it does is that, it has a config file where it keeps all of the IP address of the APIs.

1. Firstly, we will now see our nodes using

kubectl get node

If it responses, it means that your command line is working and you are getting back data.

You can even use

kubectl get nodes 

or,

kubectl get no

if you wish.

You can even get the node information in a brief or wide format with more informations

kubectl get nodes -o wide

We can also check this information in yaml

It shows all of the information!!!!!!!!

1. We will use describe command to see more informations about a node

kubectl describe node <node>

Don't copy the command. First use

kubectl get node

and copy the node name you get and then use it instead if

1. Let's check resources we have

kubectl api-resources

You can see the node has a kind "no"

Remember, we could use

kubectl get no

instead of

kubectl get node

SO, this is how this resources will help you understand short formats too.

Now , we can know much more of a particular resource using this command:

kubectl explain <type>

instead of type, we can take "node" for an example:

if we want to check the spec, we can type

kubectl explain node.spec

to get the list of all fields and sub-fields:

kubectl explain node --recursive

This command basically shows in a list format.

Some resources names to be clear about:

Note: You can use kubectl api-resources and explain to see the details of resources or check from the official documentation

But , you should be able to do both

1. Lets check out services(A service is a stable endpoint to connect to "something")

kubectl get services

or use,

kubectl get svc

Lets check out the pods:

kubectl get pods

Ahha!!!!!!! NO pods. Isn't it obvious? Have we created any containers or pods yet?

NO!!
So, how can we expect to have pods?

But, what is "default namespace" ???
Actually the commands we are using by now, use "namespace" to filter certain things. Like there are pods we did not create yet but we could not see them while using "kubectl get pods" because namespace filtered it for us.

Lets check what this namespace has got

You know what ... This kube-system thing looks suspicious.

In fact, I'm pretty sure it showed up earlier, when we did:

kubectl describe node <node-name>

So, we have pods actually.

Lets check more ..what is inside the namespace.

kubectl get pods --all-namespaces

or,

kubectl get pods -A

This output is a bit different than the "kubernetes get namespace", right?
now we can see status and many more here.

You can see the coredns, node, controller etc

SO, these are basically the control plane pods . To know more about them, you can check out this image:

Note: Till now we checked out "default" namespaces. we can change it to any particular namespace. To list only the pods in the kube-system namespace

kubectl get pods --namespace=kube-system

kubectl get pods -n kube-system

Here, -n is used to mean namespace.

More to know:

Some other basics:
kube-public: Used for installation and then connecting to something.

Lets check what is inside of it

kubectl -n kube-public get pods

There is nothing, right? So, what is this for? Actually this helps in configuring.It basically gives us interesting information of how to connect.

Let's check the config file:

kubectl -n kube-public get configmaps

We can check out any of them using "file name -o yaml" adding at the end of the previous command. Here -o is to show output

So, that was it for this blog!