Advertise Extended Resources for a Node

This page shows how to specify extended resources for a Node. Extended resources allow cluster administrators to advertise node-level resources that would otherwise be unknown to Kubernetes.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

To check the version, enter kubectl version.

Get the names of your Nodes

  1. kubectl get nodes

Choose one of your Nodes to use for this exercise.

Advertise a new extended resource on one of your Nodes

To advertise a new extended resource on a Node, send an HTTP PATCH request to the Kubernetes API server. For example, suppose one of your Nodes has four dongles attached. Here’s an example of a PATCH request that advertises four dongle resources for your Node.

  1. PATCH /api/v1/nodes/<your-node-name>/status HTTP/1.1
  2. Accept: application/json
  3. Content-Type: application/json-patch+json
  4. Host: k8s-master:8080
  6. [
  7.   {
  8.     "op": "add",
  9.     "path": "/status/capacity/example.com~1dongle",
  10.     "value": "4"
  11.   }
  12. ]

Note that Kubernetes does not need to know what a dongle is or what a dongle is for. The preceding PATCH request tells Kubernetes that your Node has four things that you call dongles.

Start a proxy, so that you can easily send requests to the Kubernetes API server:

  1. kubectl proxy

In another command window, send the HTTP PATCH request. Replace <your-node-name> with the name of your Node:

  1. curl --header "Content-Type: application/json-patch+json" \
  2.   --request PATCH \
  3.   --data '[{"op": "add", "path": "/status/capacity/example.com~1dongle", "value": "4"}]' \
  4.   http://localhost:8001/api/v1/nodes/<your-node-name>/status

Note:

In the preceding request, ~1 is the encoding for the character / in the patch path. The operation path value in JSON-Patch is interpreted as a JSON-Pointer. For more details, see IETF RFC 6901, section 3.

The output shows that the Node has a capacity of 4 dongles:

  1. "capacity": {
  2.   "cpu": "2",
  3.   "memory": "2049008Ki",
  4.   "example.com/dongle": "4",

Describe your Node:

  1. kubectl describe node <your-node-name>

Once again, the output shows the dongle resource:

  1. Capacity:
  2.   cpu: 2
  3.   memory: 2049008Ki
  4.   example.com/dongle: 4

Now, application developers can create Pods that request a certain number of dongles. See Assign Extended Resources to a Container.

Discussion

Extended resources are similar to memory and CPU resources. For example, just as a Node has a certain amount of memory and CPU to be shared by all components running on the Node, it can have a certain number of dongles to be shared by all components running on the Node. And just as application developers can create Pods that request a certain amount of memory and CPU, they can create Pods that request a certain number of dongles.

Extended resources are opaque to Kubernetes; Kubernetes does not know anything about what they are. Kubernetes knows only that a Node has a certain number of them. Extended resources must be advertised in integer amounts. For example, a Node can advertise four dongles, but not 4.5 dongles.

Storage example

Suppose a Node has 800 GiB of a special kind of disk storage. You could create a name for the special storage, say example.com/special-storage. Then you could advertise it in chunks of a certain size, say 100 GiB. In that case, your Node would advertise that it has eight resources of type example.com/special-storage.

  1. Capacity:
  2.  ...
  3.  example.com/special-storage: 8

If you want to allow arbitrary requests for special storage, you could advertise special storage in chunks of size 1 byte. In that case, you would advertise 800Gi resources of type example.com/special-storage.

  1. Capacity:
  2.  ...
  3.  example.com/special-storage:  800Gi

Then a Container could request any number of bytes of special storage, up to 800Gi.

Clean up

Here is a PATCH request that removes the dongle advertisement from a Node.

  1. PATCH /api/v1/nodes/<your-node-name>/status HTTP/1.1
  2. Accept: application/json
  3. Content-Type: application/json-patch+json
  4. Host: k8s-master:8080
  6. [
  7.   {
  8.     "op": "remove",
  9.     "path": "/status/capacity/example.com~1dongle",
  10.   }
  11. ]

Start a proxy, so that you can easily send requests to the Kubernetes API server:

  1. kubectl proxy

In another command window, send the HTTP PATCH request. Replace <your-node-name> with the name of your Node:

  1. curl --header "Content-Type: application/json-patch+json" \
  2.   --request PATCH \
  3.   --data '[{"op": "remove", "path": "/status/capacity/example.com~1dongle"}]' \
  4.   http://localhost:8001/api/v1/nodes/<your-node-name>/status

Verify that the dongle advertisement has been removed:

  1. kubectl describe node <your-node-name> | grep dongle

(you should not see any output)

What’s next

For application developers

For cluster administrators