Hei,
I'm looking for the documentation for Kubernetes's configuration files. The ones used by kubectl (e.g. kubectl create -f whatever.yaml).
Basically, the Kubernetes equivalent of this Docker Compose document.
I did search a lot but I didn't find much, or 404 links from old stackoverflow questions.
You could use the official API docs but a much more user-friendly way on the command line is the explain command, for example, I never remember what exactly goes into the spec of a pod, so I do:
$ kubectl explain Deployment.spec.template.spec
Related
I am studying "kubectl describe" sourcecodes at https://github.com/kubernetes/kubectl/blob/master/pkg/describe/describe.go
However, I still could not figure out how "kubectl decsribe [CRD]" works (as in which function/functions are called).
I am a Go newbie, so would like to get some pointers please. Thanks.
I have read describePod function and understand how it works more or less, but still could not figure out how "kubectl describe [CRD]" works.
The "kubectl describe " function can be found in the command-line interface (CLI) of Kubernetes, specifically in the "kubectl" tool. "kubectl" is used to manage and interact with a Kubernetes cluster and its resources.
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Kubectl describe command helps to view the entire information about the kubernetes resources like Pods,deployments,services,nodes,jobs etc.
By using CRD(Custom Resource Definition) you can do CRUD operations like create, update, get and delete commands to access the resources. To use CRD we need to use the API groups.
Example:
Suppose you specify an API group as example.crd.com, which means you can issue the get, list, create, update, and delete commands to access the custom resources under the API group example.crd.com.
You can use kubectl describe crd <crd_name> to get a description of the CRD.
For more information refer this official doc
Try this similar SO’s SO1 and SO2 for more information
Most Kubernetes objects can be created with kubectl create, but if you need e.g. a DaemonSet — you're out of luck.
On top of that, the objects being created through kubectl can only be customized minimally (e.g. kubectl create deployment allows you to only specify the image to run and nothing else).
So, considering that Kubernetes actually expects you to either edit a minimally configured object with kubectl edit to suit your needs or write a spec from scratch and then use kubectl apply to apply it, how does one figure out all possible keywords and their meanings to properly describe the object they need?
I expected to find something similar to Docker Compose file reference, but when looking at DaemonSet docs, I found only a single example spec that doesn't even explain most of it's keys.
The spec of the resources in .yaml file that you can run kubectl apply -f on is described in Kubernetes API reference.
Considering DeamonSet, its spec is described here. It's template is actually the same as in Pod resource.
One of the points in the kubectl best practices section in Kubernetes Docs state below:
Pin to a specific generator version, such as kubectl run
--generator=deployment/v1beta1
But then a little down in the doc, we get to learn that except for Pod, the use of --generator option is deprecated and that it would be removed in future versions.
Why is this being done? Doesn't generator make life easier in creating a template file for resource definition of deployment, service, and other resources? What alternative is the kubernetes team suggesting? This isn't there in the docs :(
kubectl create is the recommended alternative if you want to use more than just a pod (like deployment).
https://kubernetes.io/docs/reference/kubectl/conventions/#generators says:
Note: kubectl run --generator except for run-pod/v1 is deprecated in v1.12.
This pull request has the reason why generators (except run-pod/v1) were deprecated:
The direction is that we want to move away from kubectl run because it's over bloated and complicated for both users and developers. We want to mimic docker run with kubectl run so that it only creates a pod, and if you're interested in other resources kubectl create is the intended replacement.
For deployment you can try
kubectl create deployment hello-node --image=gcr.io/hello-minikube-zero-install/hello-node
and
Note: kubectl run --generator except for run-pod/v1 is deprecated in v1.12.
I have installed a K8S cluster on laptop using Kubeadm and VirtualBox. It seems a bit odd that the cluster has to be up and running to see the documentation as shown below.
praveensripati#praveen-ubuntu:~$ kubectl explain pods
Unable to connect to the server: dial tcp 192.168.0.31:6443: connect: no route to host
Any workaround for this?
See "kubectl explain — #HeptioProTip"
Behind the scenes, kubectl just made an API request to my Kubernetes cluster, grabbed the current Swagger documentation of the API version running in the cluster, and output the documentation and object types.
Try kubectl help as an offline alternative, but that won't be as complete (limite to kubectl itself).
So the rather sobering news is that AFAIK there's not out-of-the box way how to do it, though you could totally write a kubectl plugin (it has become rather trivial now in 1.12). But for now, the best I can offer is the following:
# figure out which endpoint kubectl uses to retrieve docs:
$ kubectl -v9 explain pods
# from above I learn that in my case it's apparently
# https://192.168.64.11:8443/openapi/v2 so let's curl that:
$ curl -k https://192.168.64.11:8443/openapi/v2 > resources-docs.json
From here you can, for example, use jq to query for the descriptions. It's not as nice as a proper explain, but kinda is a good enough workaround until someone writes an docs offline query kubectl plugin.
The 'explain' documentation lives in the kube-apiserver and its resource definitions. Hence the need to connect to it through kubectl explain to get any docs. This is different from the standard very basic cli help from kubectl where it's in the kubectl Golang code.
So no workaround really other than setting up a dummy Kubernetes cluster and have kubectl point to it. Please note that CRDs help might not be available since they live in the deployed CRDs themselves.
Is there a kubectl command that gives advice about essential fields required in the YAML, or YAML examples, for a given resource?
Currently, when I want a YAML example of a resource, for example a deployment, I search the online documentation. I'd rather stay in the terminal.
kubectl explain deployment works for resources which publish openapi specs.