Get a specific apiVersion manifest from k8s

TL;DR

To get a manifest from k8s in any supported API version you can use an extended kubectl get notation like kubectl get deployments.v1beta1.extensions mydeploy -o yaml

Briefly and with examples

Everybody knows how to get a resource manifest from Kubernetes. But do you know that you can put a manifest with one apiVersion set and get the same resource manifest with another apiVersion back?

Imagine

1. You have a deployment in a cluster, that uses api-version extensions/v1beta1 from a git repo.

2. You've updated the cluster (1.15 => 1.16). Old deployment works fine, but you can't deploy nothing new with the old manifest because in k8s 1.16 api-version extensions/v1beta1 is absent.

3. You have two options:

   1. Rewrite it manually or

   2. Get it from the cluster in updated spec format (apps/v1)

To get manifest from k8s you can:

below there is an example for v1.15, where extensions/v1beta1 is not removed yet

# from extensions
kubectl get deployments.extensions ext -o yaml
# from extensions, but for v1beta1
kubectl get deployments.v1beta1.extensions ext -o yaml
# from apps
kubectl get deployments.apps ext -o yaml
# from apps, but v1
kubectl get deployments.v1.apps ext -o yaml

Notice that if you do just kubectl get deployments ext -o yaml, you will get a manifest from extensions/v1beta1 nevertheless you've even applied apps/v1 before. Details here.

Prove it

1. Start 1.15

    minikube start --kubernetes-version=v1.15.12
   

2. Make 2 manifests for deployments with different versions. Note the absence of spec.selector in extensions/v1beta1

    apiVersion: apps/v1
    kind: Deployment
    metadata:
      creationTimestamp: null
      labels:
        run: apps
      name: apps
    spec:
      replicas: 1
      selector:
        matchLabels:
          run: apps
      template:
        metadata:
          creationTimestamp: null
          labels:
            run: apps
        spec:
          containers:
          - image: nginx
            name: apps
    ---
    apiVersion: extensions/v1beta1
    kind: Deployment
    metadata:
      labels:
        run: ext
      name: ext
    spec:
      replicas: 1
      template:
        metadata:
          creationTimestamp: null
          labels:
            run: ext
        spec:
          containers:
          - image: nginx
            name: ext
   

3. Apply

    ❯ minikube kubectl -- apply -f .
    deployment.apps/apps created
    deployment.extensions/ext created
   

4. Check that resources apps and ext are in extensions/v1beta1 and in apps/v1 too

   • The hard way - curl:

    ❯ minikube kubectl -- proxy
    Starting to serve on 127.0.0.1:8001
    ❯ curl -s 127.0.0.1:8001/apis/extensions/v1beta1/namespaces/default/deployments/apps | yq . --yaml-output
    kind: Deployment
    apiVersion: extensions/v1beta1
    # ...
    ❯ curl -s 127.0.0.1:8001/apis/extensions/v1beta1/namespaces/default/deployments/ext | yq . --yaml-output
    kind: Deployment
    apiVersion: extensions/v1beta1
    # ...
    ❯ curl -s 127.0.0.1:8001/apis/apps/v1/namespaces/default/deployments/apps | yq . --yaml-output
    kind: Deployment
    apiVersion: apps/v1
    # ...
    ❯ curl -s 127.0.0.1:8001/apis/apps/v1/namespaces/default/deployments/ext | yq . --yaml-output
    kind: Deployment
    apiVersion: apps/v1
    # ...

• Or kubectl:

    # from extensions
    kubectl get deployments.extensions ext -o yaml
    # from extensions, but v1beta1
    kubectl get deployments.v1beta1.extensions ext -o yaml
    # from apps
    kubectl get deployments.apps ext -o yaml
    # from apps, but v1
    kubectl get deployments.v1.apps ext -o yaml

Bonus: kubectl explain

If you do kubectl explain deployment than (surprise!) you'll get a description for extensions/v1beta1. Because kubectl explain works the same way, just like kubectl get:

If you want a specific version, use an --api-version flag :

minikube kubectl -- explain deployment.spec --api-version apps/v1
minikube kubectl -- explain deployment.spec --api-version extensions/v1beta1