Kubectl: Useful shortcuts

Context

kubectl is the command line tool for accessing and interacting with your Kubernetes cluster. It's quite intuitive and easy-to-use, but here is a small summary of some very useful commands to get you started if you're new to Kube.

You should already know a few basics about building a Docker container and firing a simple deployment on Kubernetes though. This won't help you much if you don't know Kubernetes at all :-)

Anyway, here's a quick catch-up:

• To deploy a basic app on Kube, you would typically write a Deployment, featuring a template with a list of Containers.
• Once applied, this Deployment will have an associated ReplicaSet linked to the template you specified, and managed by Kube.
• Each ReplicaSet will then create Pods accordingly (depending on the amount of replicas you set).
• And finally, each Pod will wrap the Containers you specified in the aforementioned template.
• Additionally, Services will provide a single Endpoint to your app inside your cluster, while Ingresses will provide access from outside your cluster, redirecting traffic to the Service.

I'll try to update this article if I discover or remember some good shortcuts. It would be pretty long and tedious if it was a full tutorial, so I'll keep this light.

A good entrypoint

kubectl explain is here to help you. You can use it on any kind of ressources inside Kubernetes:

kubectl explain deployments

This is really useful, especially when combined with some IDE plugins. VSCode has some that add snippets, and even a cluster visualizer that lets you browse all your ressources from inside your editor! You can easily learn something about a new type of ressource you didn't know about.

A simple way to open a TTY to your pod

You may already know that you can open a terminal over SSH by simply running:

kubectl exec -it my-app-1234-5678 -- /bin/sh

If you're deploying quite often, the replicaset attached to your deployment will change, and pods will be recreated. Therefore, opening a new TTY can be tedious.

But fortunately, you can use the service as a shortcut:

kubectl exec -it service/my-app -- /bin/sh

Accessing multiple apps logs

You may know that you can access a container logs, either statically or continuously, by running this:

kubectl logs [-f] my-app-1234-5678 container_name

But yet again, the pod may be replaced, and you may be interested to fetch logs from multiple pods of the same app, or even logs coming from various apps, but serving a common purpose.

You can do just that by adding Labels to your ressources (especially deployments), and running the same command, but with Label Selectors instead:

kubectl logs [-f] -l app=my-app -c container_name

In fact, selectors can be used with many commands, including all get calls, to fetch ressources of different nature grouped by-whatever-your-semantic-grouping-is. No more grep :-)