How to deserialize Kubernetes YAML file

Question

How can I deserialize a Kubernetes YAML file into an Go struct? I took a look into the kubectl code, but somehow I get an error for every YAML file:

no kind "Deployment" is registered for version "apps/v1beta1"

This is an MWE:

package main

import (
    "fmt"

    "k8s.io/client-go/pkg/api"
)

var service = `
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: my-nginx
spec:
  replicas: 2
  template:
    metadata:
      labels:
        run: my-nginx
    spec:
      containers:
      - name: my-nginx
        image: nginx
        ports:
        - containerPort: 80
`

func main() {
    decode := api.Codecs.UniversalDecoder().Decode
    //decode := api.Codecs.UniversalDeserializer().Decode

    obj, _, err := decode([]byte(service), nil, nil)
    if err != nil {
        panic(err)
    }

    fmt.Printf("%#v\n", obj)
}

I am using client version 2.0.0. The glide.yaml looks like this:

package: test/stackoverflow
import:
- package: k8s.io/client-go
  version: ^2.0.0

These are the references to kubectl:

• https://github.com/kubernetes/kubernetes/blob/43ac38e29e6ecf83e78bc7c5d9f804310b051c95/pkg/kubectl/cmd/apply.go#L637
• https://github.com/kubernetes/kubernetes/blob/43ac38e29e6ecf83e78bc7c5d9f804310b051c95/pkg/kubectl/cmd/util/factory_client_access.go#L205-L213

Unfortunately, the docs are very confusing to me, so I have no idea how to tackle this problem.

Edit:

This problem also exists with other resource types:

• no kind "Service" is registered for version "v1"

Answer 1

You need to import _ "k8s.io/client-go/pkg/apis/extensions/install" otherwise the schema is empty, see also docs.

The complete working example is:

$ go get -u github.com/golang/dep/cmd/dep
$ dep init
$ go run main.go

With the following main.go:

package main

import (
    "fmt"

    "k8s.io/client-go/pkg/api"
    _ "k8s.io/client-go/pkg/api/install"
    _ "k8s.io/client-go/pkg/apis/extensions/install"
)

var deployment = `
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: my-nginx
spec:
replicas: 2
template:
  metadata:
    labels:
      run: my-nginx
  spec:
    containers:
    - name: my-nginx
      image: nginx
      ports:
      - containerPort: 80
`

func main() {
    // decode := api.Codecs.UniversalDecoder().Decode
    decode := api.Codecs.UniversalDeserializer().Decode

    obj, _, err := decode([]byte(deployment), nil, nil)
    if err != nil {
        fmt.Printf("%#v", err)
    }

    fmt.Printf("%#v\n", obj)
}

Note that I also imported _ "k8s.io/client-go/pkg/api/install" for you so that you can use objects in v1 such as pods or services.

EDIT: Kudos to my colleague Stefan Schimanski who proposed the initial solution.

Answer 2

I've been using api machinery'sk8s.io/apimachinery/pkg/util/yaml to decode kubernete's deployment and service manifests.

import (
   "fmt"
   "bytes"
   appsv1 "k8s.io/api/apps/v1"
    k8Yaml "k8s.io/apimachinery/pkg/util/yaml"
)
...

d := &appsv1.Deployment{}
dec := k8Yaml.NewYAMLOrJSONDecoder(bytes.NewReader([]byte(deploymentManifest)), 1000)

if err := dec.Decode(&d); err != nil {
        return nil, err
}

fmt.Printf("%+v", d)