cachier

Cachier

Cachier is an experimental Kubernetes operator that watches "duck-typed" Kubernetes resources and instantiates Knative's Image "cache` resources for any embedded image references.

The name is a play on the the word "cashier" and the purpose: caching.

You can read more about Knative duck-typing here (access guarded by membership in knative-users@googlegroups.com).

The shape of supported resources

Numerous built-in Kubernetes resources implement this duck-type including: Deployment, ReplicaSet, StatefulSet, DaemonSet, and Job. The expected shape is:

metadata:
  # Standard K8s metadata

spec:
  template:
    metadata:
      # Pod metadata
    spec:
      # Pod spec

How it works

As the operator processes these resources, it creates a Knative resource of type caching.internal.knative.dev/v1alpha1/Image for each of the containers in the "pod spec".

Paired with an implementation of this resource (e.g. the WarmImage poc-cache implementation) the latency effect of pulling images on pod starts should be significantly mitigated.

Try it out

While this is not intended for public use, you can try it out via:

curl https://raw.githubusercontent.com/mattmoor/cachier/master/release.yaml \
  | kubectl apply -f -

Then you can see the effects with:

# Start a dummy deployment
kubectl create namespace demo
kubectl -ndemo run dummy --image=ubuntu --command -- /bin/bash -c "sleep 2592054"

# See the creating image resource:
kubectl -ndemo get image -oyaml

This should show something like:

kubectl -ndemo get image -oyaml
apiVersion: v1
items:
- apiVersion: caching.internal.knative.dev/v1alpha1
  kind: Image
  metadata:
    clusterName: ""
    creationTimestamp: 2018-10-08T01:58:30Z
    generateName: dummy-00-
    generation: 1
    labels:
      controller: a792cd10-ca9d-11e8-b5eb-42010af000a3
      generation: "00001"
    name: dummy-00-nn44b
    namespace: demo
    ownerReferences:
    - apiVersion: apps/v1
      blockOwnerDeletion: true
      controller: true
      kind: Deployment
      name: dummy
      uid: a792cd10-ca9d-11e8-b5eb-42010af000a3
    resourceVersion: "26625108"
    selfLink: /apis/caching.internal.knative.dev/v1alpha1/namespaces/demo/images/dummy-00-nn44b
    uid: a7963987-ca9d-11e8-b5eb-42010af000a3
  spec:
    image: ubuntu
  status: {}
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

Configuring the resources considered

You can customize the collection of resources to which this controller applies by changing the following flag passed to the controller binary:

        # Add PodSpecable types here:
        - "-resource=Deployment.v1.apps"
        - "-resource=ReplicaSet.v1.apps"
        - "-resource=StatefulSet.v1.apps"
        - "-resource=DaemonSet.v1.apps"

These have the form {Kind}.{version}.{group}, so for example a resource like:

apiVersion: foo.mattmoor.io/v1beta2
kind: Bar

Would be passed as: Bar.v1beta2.foo.mattmoor.io

Excluding resources from consideration

You can exclude individual resources from consideration by annotating them with:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: foo
  namespace: bar
  # This annotation excludes resources from consideration.
  annotations:
    cachier.mattmoor.io/decorate: disable