Network Resources Injector

Network Resources Injector is a Kubernetes Dynamic Admission Controller application that provides functionality of patching Kubernetes pod specifications with requests and limits of custom network resources (managed by device plugins such as k8snetworkplumbingwg/sriov-network-device-plugin).

Getting started

To quickly build and deploy admission controller run:

make image
kubectl apply -f deployments/auth.yaml \
              -f deployments/server.yaml

For full installation and troubleshooting steps please see Installation guide.

Network resources injection example

To see mutating webhook in action you're going to need to add custom resources to your Kubernetes node. In real life scenarios you're going to use network resources managed by network devices plugins, such as k8snetworkplumbingwg/sriov-network-device-plugin. There should be net-attach-def CRD already created before you start. In a terminal window start proxy, so that you can easily send HTTP requests to the Kubernetes API server:

kubectl proxy

In another terminal window, execute below command to add 4 example.com/foo resources. Remember to edit <node-name> to match your cluster environment.

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

Next, you need to create a net-attach-def linked to this example.com/foo resource. To achieve that execute below command:

cat <<EOF | kubectl create -f -
apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  annotations:
    k8s.v1.cni.cncf.io/resourceName: example.com/foo
  name: foo-network
  namespace: default
spec:
  config: |
    {
      "cniVersion": "0.3.0",
      "name": "foo-network",
      "type": "bridge",
      "bridge": "br0",
      "isGateway": true,
      "ipam":
      {
        "type": "host-local",
        "subnet": "172.36.0.0/24",
        "dataDir": "/mnt/cluster-ipam"
      }
    }
EOF

Finally, schedule a pod that will take advantage of automated network resources injection. Use below example, to attach 2 foo-network networks and inject resources accordingly.

cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
  name: webhook-demo
  annotations:
    k8s.v1.cni.cncf.io/networks: foo-network, foo-network
spec:
  containers:
  - image: busybox
    resources:
    command: ["tail", "-f", "/dev/null"]
    imagePullPolicy: IfNotPresent
    name: busybox
  restartPolicy: Always
EOF

Now verify that resources requests/limits have been properly injected into the first container in the pod. If you have jq installed run this command:

kubectl get pod webhook-demo -o json | jq .spec.containers[0].resources

Expected output showing injected resources in the pod spec, depsite the fact that we have only defined k8s.v1.cni.cncf.io/networks annotation.

{
  "limits": {
    "example.com/foo": "2"
  },
  "requests": {
    "example.com/foo": "2"
  }
}

Alternatively, grep output of kubectl to get the same information.

kubectl get pod webhook-demo -o yaml | grep resources -A4
    resources:
      limits:
        example.com/foo: "2"
      requests:
        example.com/foo: "2"

As the last step perform cleanup by removing net-attach-def, pod and custom example.com/foo resources. To do that, simply run:

curl --header "Content-Type: application/json-patch+json" \
     --request PATCH \
     --data '[{"op": "remove", "path": "/status/capacity/example.com~1foo"}]' \
     http://localhost:8001/api/v1/nodes/<node-name>/status
kubectl delete net-attach-def foo-network
kubectl delete pod webhook-demo

Vendoring

To create the vendor folder invoke the following which will create a vendor folder.

make vendor

Security

Disable adding client CAs to server TLS endpoint

If you wish to not add any client CAs to the servers TLS endpoint, add --insecure flag to webhook binary arguments (See server.yaml).

Client CAs

By default, we consume the client CA from the Kubernetes service account secrets directory /var/run/secrets/kubernetes.io/serviceaccount/. If you wish to consume a client CA from a different location, please specify flag --client-ca with a valid path. If you wish to add more than one client CA, repeat this flag multiple times. If --client-ca is defined, the default client CA from the service account secrets directory will not be consumed.

Additional features

Expose Hugepages via Downward API

In Kubernetes 1.20, an alpha feature was added to expose the requested hugepages to the container via the Downward API. Being alpha, this feature is disabled in Kubernetes by default. If enabled when Kubernetes is deployed via FEATURE_GATES="DownwardAPIHugePages=true", then Network Resource Injector can be used to mutate the pod spec to publish the hugepage data to the container. To enable this functionality in Network Resource Injector, add --injectHugepageDownApi flag to webhook binary arguments (See server.yaml).

Like the other Downward API provided data, hugepage information for a pod can be located by an application at the path /etc/podnetinfo/ in the container's file system. This directory will contain the request and limit information for 1Gi/2Mb.

1Gi Hugepages:

    Requests: /etc/podnetinfo/hugepages_1G_request_${CONTAINER_NAME}
    Limits: /etc/podnetinfo/hugepages_1G_limit_${CONTAINER_NAME}

2Mb: Hugepages:

    Requests: /etc/podnetinfo/hugepages_2M_request_${CONTAINER_NAME}
    Limits: /etc/podnetinfo/hugepages_2M_limit_${CONTAINER_NAME}

NOTE: To aid the application, when hugepage fields are being requested via the Downward API, Network Resource Injector also mutates the pod spec to add the environment variable CONTAINER_NAME with the container's name applied.

Node Selector

If a NetworkAttachmentDefinition CR annotation k8s.v1.cni.cncf.io/nodeSelector is present and a pod utilizes this network, Network Resources Injector will add this node selection constraint into the pod spec field nodeSelector. Injecting a single node selector label is currently supported.

Example:

apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  name: test-network
  annotations:
    k8s.v1.cni.cncf.io/nodeSelector: master=eno3
spec:
  config: '{
  "cniVersion": "0.3.1",
  "type": "macvlan",
  "master": "eno3",
  "mode": "bridge",
  }'
...

Pod spec after modification by Network Resources Injector:

apiVersion: v1
kind: Pod
metadata:
  name: testpod
  annotations:
    k8s.v1.cni.cncf.io/networks: test-network
spec:
 ..
 nodeSelector:
   master: eno3

Contact Us

For any questions about Network Resources Injector, feel free to ask a question in #network-resources-injector in NPWG slack, or open up a GitHub issue.