#Snippets

Topics

August 02, 2020

#Read Kubernetes API data using Golang

kubernetes golang development server-side

Get the API client.

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

// use the current context in kubeconfig
config, err := clientcmd.BuildConfigFromFlags("", "<path_to_KUBECONFIG>")
if err != nil {
  panic(err.Error())
}

// create the clientset
clientset, err := kubernetes.NewForConfig(config)
if err != nil {
  panic(err.Error())
}

Usage examples:

read data about servers

nodeList, err := clientset.CoreV1().Nodes().List(context.TODO(), metav1.ListOptions{})
if err != nil {
  panic(err.Error())
}

read data about pods

namespace := "example"  // leave empty to get data from all namespaces
podList, err := clientset.CoreV1().Pods(namespace).List(context.TODO(), metav1.ListOptions{})
if err != nil {
  panic(err.Error())
}

In the above examples, ListOptions can take two important strings, field selectors and label selectors. This can be used for filtering results.

metav1.ListOptions{
  LabelSelector: "labelName=labelKey",
  FieldSelector: "spec.nodeName=<node_name>",  // Example for filtering by node name
}

Field selectors and label selectors on this case operate in the same way that the CLI options for kubectl do. So, the same rules apply here.

#Read Kubernetes metrics-server data using Golang

kubernetes golang development server-side

First, get the metrics API client.

import (
  "fmt"
  "context"
  "k8s.io/client-go/kubernetes"
  "k8s.io/client-go/tools/clientcmd"
  metricsv "k8s.io/metrics/pkg/client/clientset/versioned"
)

// Get the config
config, err := clientcmd.BuildConfigFromFlags("", "<path_to_KUBECONFIG>")
if err != nil {
  panic(err.Error())
}

// Get the metrics client
metricsClientset, err := metricsv.NewForConfig(config)
if err != nil {
  panic(err.Error())
}

Get the data and store it in podMetricsList array.

namespace := "example"  // leave empty to get data from all namespaces
podMetricsList, err := metricsClientset.MetricsV1beta1().PodMetricses(namespace).List(context.TODO(), metav1.ListOptions{})
if err != nil {
  panic(err.Error())
}

Iterate over the results found.

for _, v := range podMetricsList.Items {
  fmt.Printf("%s\n", v.GetName())
  fmt.Printf("%s\n", v.GetNamespace())
  fmt.Printf("%vm\n", v.Containers[0].Usage.Cpu().MilliValue())
  fmt.Printf("%vMi\n", v.Containers[0].Usage.Memory().Value()/(1024*1024))
}

Note: if you’re inspecting pods that may have more than one container, you’ll need to iterate over v.Containers as well.

July 16, 2020

#Bootstrap a Go Cobra application with Go Modules

development golang

To bootstrap a Go application using Cobra Generator and Go Modules, start by installing the Cobra command line:

# Install Cobra
go get github.com/spf13/cobra/cobra

Initialize your Cobra project, but remember to use your package’s fully qualified name, as in: github.com/laurybueno/kubectl-hoggers. Don’t worry if your package is not publicly available yet. And there is no need to put your source code inside GOPATH anymore (since Go 1.11 at least):

cobra init --pkg-name <fully_qualified_package_name>

Initialize your new module:

go mod init <fully_qualified_package_name>

Get recursively all its dependencies and install it:

go get -d -v ./...
go install -v ./...

Your app’s command line is now ready to be used:

kubectl-hoggers

<laury.dev/>

#Snippets

#Read Kubernetes API data using Golang

Further reading

#Read Kubernetes metrics-server data using Golang

#Bootstrap a Go Cobra application with Go Modules

Further reading