How to retrieve kubernetes metrics via client-go and golang

Question

I want to access metrics from kubernetes with golang. Something like cpu and memory per node as well as the same for pods and/or namespaces.

I am kind of lost here because the documentation is not as clear as it could be.

I have learned that there is heapster (which is deprecated according to the github repo). There is also metric server and a rest api.

Where can I find some examples to get started? I do not want to install another app, package or service in kubernetes. I'd like to get the information as native as possible. What is the preferred way to access these information with client-go and golang?

Answer 1

There's a much better API for this: https://github.com/kubernetes/metrics. Using this, you don't have to create the data structs or handle row byte slices.

import (
  metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
  metricsv "k8s.io/metrics/pkg/client/clientset/versioned"
  ...
)

...
clientset, err := metricsv.NewForConfig(config)
podMetricsList, err := clientset.MetricsV1beta1().PodMetricses("").List(metav1.ListOptions{})

Answer 2

As explained in the question, the documentations are not clear for a beginner. Even go-client examples retrieve the data, I wanted to get Type support.

As it explained by above answer, you can get the data in []byte in JSON format. This is how I did it.

package main

import (
    "encoding/json"
    "fmt"
    "time"

    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/rest"
)

// PodMetricsList : PodMetricsList
type PodMetricsList struct {
    Kind       string `json:"kind"`
    APIVersion string `json:"apiVersion"`
    Metadata   struct {
        SelfLink string `json:"selfLink"`
    } `json:"metadata"`
    Items []struct {
        Metadata struct {
            Name              string    `json:"name"`
            Namespace         string    `json:"namespace"`
            SelfLink          string    `json:"selfLink"`
            CreationTimestamp time.Time `json:"creationTimestamp"`
        } `json:"metadata"`
        Timestamp  time.Time `json:"timestamp"`
        Window     string    `json:"window"`
        Containers []struct {
            Name  string `json:"name"`
            Usage struct {
                CPU    string `json:"cpu"`
                Memory string `json:"memory"`
            } `json:"usage"`
        } `json:"containers"`
    } `json:"items"`
}

func getMetrics(clientset *kubernetes.Clientset, pods *PodMetricsList) error {
    data, err := clientset.RESTClient().Get().AbsPath("apis/metrics.k8s.io/v1beta1/pods").DoRaw()
    if err != nil {
        return err
    }
    err = json.Unmarshal(data, &pods)
    return err
}

func main() {
    // creates the in-cluster config
    // https://github.com/kubernetes/client-go/tree/master/examples#configuration
    config, err := rest.InClusterConfig()
    if err != nil {
        panic(err.Error())
    }
    // creates the clientset
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        panic(err.Error())
    }
    var pods PodMetricsList
    err = getMetrics(clientset, &pods)
    if err != nil {
        panic(err.Error())
    }
    for _, m := range pods.Items {
        fmt.Println(m.Metadata.Name, m.Metadata.Namespace, m.Timestamp.String())
    }
}

Install following Go packages: go get -u k8s.io/client-go/kubernetes k8s.io/client-go/rest

You can use following endpoints to retrieve the data as you want;

• Nodes: apis/metrics.k8s.io/v1beta1/nodes
• Pods: apis/metrics.k8s.io/v1beta1/pods
• Pods of default namespace: apis/metrics.k8s.io/v1beta1/namespaces/default/pods
• Specific Pod: /apis/metrics.k8s.io/v1beta1/namespaces/default/pods/<POD-NAME>

NOTE: You may need to change the Type before json.Unmarshal. You can define the Type only for the field which you are interested with.