programming kubernetes chapter 3 - client-go [c45d33e0]

Tags: hausenblas - programming kubernetes

• Overview: controllers can be constructed by calling the client-go library, which provides a set of sensible defaults such as work queues and informers

• github.com/kubernetes/client-go

  • most api types can be found under github.com/kubernetes/client-go/tree/master/listers
• api definitions: github.com/kubernetes/api

• github.com/kubernetes/apimachinery - generic building blocks to kube-like API, not restricted to container management

  • most of the generic API types (ObjectMeta, TypeMeta, GetOptions, ListOptions) are in github.com/kubernetes/apimachinery/tree/master/pkg/apis/meta/v1

  // basic client

  import (
      metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
      "k8s.io/client-go/tools/clientcmd"
      "k8s.io/client-go/kubernetes"
  )

  kubeconfig = flag.String("kubeconfig, "~/.kube/config", "kubeconfig file")
  flag.Parse()
  config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
  clientset, err := kubernetes.NewForConfig(config)

  pod, err := clientset.CoreV1().Pods("book").Get("example", metav1.GetOptions{})

This parses the appropriate kubeconfig and then gets the pods using the GetOptions

If you run a binary inside of a pod inside a cluster, kubelet automatically mounts a sservice account into /var/run/secrets/kubernetes.io/serviceaccount

CRUD operations are run through the XOptions, such as CreateOptions or DeleteOptions. ALl of htem are part of ObjectMeta

• alpha/beta/vN verisons are what you would expect (alpha changes, beta is unlikely to break, vN is stable)
• each object stored in etcd is stored as a specific version known as the storage version of that resource

• anything served as a kind is a struct

  • all objects can be retrived and deepcopied
  • each object stores its groupversionkind

  type Pod struct {
      metav1.TypeMeta `json:",inline"`

      metav1.ObjectMeta `json:"metadata,omitempty"`

      Spec PodSpec `json:"spec,omitempty"`

      Status PodStatus `json:"status,omitempty"`
  }