k8s how to update specific value in secret

I need to update a secret with specific value,(the secret contain additional data) my question is how I can update just the value and not all the secret data (I don't want to override the existing data). I mean if the secret have additional values I don’t want to override them just the entry foo

updSec := v1.Secret{
	TypeMeta: metav1.TypeMeta{},
	ObjectMeta: metav1.ObjectMeta{
		Name:      "d-values",
		Namespace: "terv”,
	},
	Immutable:  nil,
	Data:       nil,
	StringData: nil,
	Type:       "Opaque",
}
updSec.Data[“foo”] = newVal
if err := r.Client.Update(ctx, &updSec); err != nil {
	return ctrl.Result{}, err
}

The issue is that the secret is already exist and here im creating new object and not sure how to do it right ...I need for secret that called d-values just update the newVal for key foo

update

when trying the code in the answer after I run the

patch, err := yaml.Marshal(updSec)
the data looks like following
and the patch are failed with error, any idea if its related ?

if I try with the c.Client.Update it works but not with Patch but the Patch is the right way as if I've ties before is should keep them..

I don't think you can update a single key using the Update method, but you can certainly do that using Patch instead. Here's an example that uses a StrategicMergePatch; it will replace the key val2 in a secret with the value newval:

package main

import (
  "context"
  "encoding/json"
  "flag"
  "fmt"
  "path/filepath"

  v1 "k8s.io/api/core/v1"
  metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
  "k8s.io/apimachinery/pkg/types"
  "k8s.io/client-go/kubernetes"
  "k8s.io/client-go/tools/clientcmd"
  "k8s.io/client-go/util/homedir"
)

func main() {
  var kubeconfig *string
  var namespace *string
  var secretname *string

  namespace = flag.String("namespace", "", "namespace of secret")
  secretname = flag.String("name", "", "name of secret")

  if home := homedir.HomeDir(); home != "" {
    kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional) absolute path to the kubeconfig file")
  } else {
    kubeconfig = flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
  }

  flag.Parse()

  if *namespace == "" {
    panic(fmt.Errorf("you must specify a namespace"))
  }

  if *secretname == "" {
    panic(fmt.Errorf("you must specify a secret name"))
  }

  config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
  if err != nil {
    panic(err)
  }

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

  secretClient := clientset.CoreV1().Secrets(*namespace)
  ctx := context.TODO()

  updSec := v1.Secret{
    Data: map[string][]byte{
      "val2": []byte("newval"),
    },
  }

  payloadBytes, err := json.Marshal(updSec)
  if err != nil {
    panic(err)
  }

  if _, err = secretClient.Patch(ctx, *secretname,
    types.StrategicMergePatchType, payloadBytes, metav1.PatchOptions{}); err != nil {
    panic(err)
  }

  // Fetch updated secret
  sec, err := secretClient.Get(ctx, *secretname, metav1.GetOptions{})
  if err != nil {
    panic(err)
  }
  secJson, err := json.MarshalIndent(sec, "", "  ")
  if err != nil {
    panic(err)
  }

  fmt.Print(string(secJson))
}

For example, if I create a secret like this:

kubectl create secret generic \
--from-literal val1=key1 \
--from-literal val2=key2 example

And then run the above code like this:

go run main.go -namespace default -name example

The code will output the update secret. Looking at the data section, we see:

  "data": {
"val1": "a2V5MQ==",
"val2": "bmV3dmFs"
},

And if we decode val2 we see:

$ kubectl get secret example -o json | jq '.data.val2|@base64d'
"newval"

Using the Operator SDK

If you're working with the Operator SDK, you can use Update if you're first reading the existing value, like this:

  // Read the existing secret
secret := &corev1.Secret{}
if err := r.Get(ctx, req.NamespacedName, secret); err != nil {
panic(err)
}
// Check if it needs to be modified
val, ok := secret.Data["val2"]
// If yes, update the secret with a new value and then write
// the entire object back with Update
if !ok || !bytes.Equal(val, []byte("val2")) {
ctxlog.Info("needs update", "secret", secret)
secret.Data["val2"] = []byte("newval")
if err := r.Update(ctx, secret); err != nil {
panic(err)
}
}

You can use the Patch method if you only want to submit a partial update:

  if !ok || !bytes.Equal(val, []byte("val2")) {
ctxlog.Info("needs update", "secret", secret)
newVal := corev1.Secret{
Data: map[string][]byte{
"val2": []byte("newval"),
},
}
patch, err := json.Marshal(newVal)
if err != nil {
panic(err)
}
if err := r.Client.Patch(ctx, secret, client.RawPatch(types.StrategicMergePatchType, patch)); err != nil {
panic(err)
}
}

This is pretty much identical to the earlier example. There are examples of using the client.Patch method in the docs, but I'll be honest, I don't find the example very clear.