Meeting kubectl
The commands you use every day.
Kube control, written k u b e c t l, is the tool you will use more than any other. It turns your typing into requests for the A P I server. The good news is that it follows a very regular pattern, so you can learn it quickly. In this lesson, we learn that pattern.
- One tool for everything
- A simple, regular pattern
- Learn it once, use it forever
The kubectl pattern
Almost every command has the same shape. First comes kube control. Then a verb, what you want to do, like get, create, delete, describe, or apply. Then a resource type, what you want to act on, like pods, deployments, or services. And last, optionally, a name, and some flags. So, kube control get pods, lists pods. Kube control delete pod web, deletes the pod named web. Once you see the pattern, a new command is never a surprise.
Reading the cluster
Let's read the cluster. The get verb lists resources. Here are the namespaces, which are folders that group objects, and here, the nodes. Kubernetes knows many resource types, and the command, A P I resources, lists all of them, with their short names. For example, pods can be shortened to p o, services to s v c, and deployments to deploy. Short names save a lot of typing.
kubectl get namespaces NAME STATUS AGE default Active 14m kube-node-lease Active 14m kube-public Active 14m kube-system Active 14m kubectl get nodes NAME STATUS ROLES AGE VERSION k8s Ready control-plane 14m v1.34.0 k8s-m02 Ready <none> 14m v1.34.0 k8s-m03 Ready <none> 14m v1.34.0 kubectl api-resources | head -8 | cut -c1-100 NAME SHORTNAMES APIVERSION NAMESPACED KIND bindings v1 true Bind componentstatuses cs v1 false Comp configmaps cm v1 true Conf endpoints ep v1 true Endp events ev v1 true Even limitranges limits v1 true Limi namespaces ns v1 false Name
The verbs you will use most
Here are the verbs that you will use daily. Get, to list things. Describe, to see full details and recent events, and it is the best debugging command. Create and apply, to make things, and we will compare them later. Delete, to remove things. Logs, to read what a container printed. Exec, to run a command inside a container. And explain, which is built in documentation, for any field, so you almost never need to search the web.
| Verb | What it does |
|---|---|
| get | list resources |
| describe | details and recent events |
| apply | create or update from a file |
| delete | remove resources |
| logs | read container output |
| exec | run a command in a container |
| explain | built-in documentation |
Documentation in your terminal
The explain command is a hidden gem. Let's ask about a pod. It prints the description of the object straight from the cluster's own schema, so it always matches your version. We can go deeper, by following the dots. Asking for pod dot spec dot containers, explains that field, and so on, all the way down. When you forget what a field means, ask the cluster.
kubectl explain pod | head -12 KIND: Pod VERSION: v1 DESCRIPTION: Pod is a collection of containers that can run on a host. This resource is created by clients and scheduled onto hosts. FIELDS: apiVersion <string> APIVersion defines the versioned schema of this representation of an object. Servers should convert recognized schemas to the latest internal value, and may reject unrecognized values. More info: kubectl explain pod.spec.containers | head -12 KIND: Pod VERSION: v1 FIELD: containers <[]Container> DESCRIPTION: List of containers belonging to the pod. Containers cannot currently be added or removed. There must be at least one container in a Pod. Cannot be updated. A single application container that you want to run within a pod.
Summary
Excellent. Kube control follows one pattern, verb, resource, name. Get lists, describe explains, apply creates, delete removes, and explain documents. Now we are ready for the big moment, running our very first pod.
Key takeaways- Pattern: verb + resource + name
- get and describe to look
- explain is built-in documentation