Understanding snapshots for Azure Kubernetes Fleet Manager cluster resource placement

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Fleet Manager keeps a history of the 10 most recently used placement scheduling policies, along with resource versions the placement selected. These policy and resource versions are held as ClusterSchedulingPolicySnapshot and ClusterResourceSnapshot objects respectively.

In this article, we explore these objects so you can understand them should you wish to work with them.

Note

If you aren't already familiar with Fleet Manager's cluster resource placement (CRP), read the conceptual overview of resource placement before reading this article.

Viewing resource snapshots

You can view the resource snapshots held by Fleet Manager using the following steps when connected to the Fleet Manager hub cluster.

For this sample we use a ConfigMap resource that we have modified, leading to two snapshots.

kubectl get clusterresourcesnapshots --show-labels

We see two snapshots, with the most recent one marked as the latest (kubernetes-fleet.io/is-latest-snapshot=true), with a resource-index of 1 (kubernetes-fleet.io/resource-index=1).

NAME                           GEN   AGE    LABELS
example-placement-0-snapshot   1     17m    kubernetes-fleet.io/is-latest-snapshot=false,kubernetes-fleet.io/parent-CRP=example-placement,kubernetes-fleet.io/resource-index=0
example-placement-1-snapshot   1     2m2s   kubernetes-fleet.io/is-latest-snapshot=true,kubernetes-fleet.io/parent-CRP=example-placement,kubernetes-fleet.io/resource-index=1

We can inspect the contents of the example-placement-1-snapshot snapshot as follows.

kubectl get clusterresourcesnapshots example-placement-1-snapshot -o yaml

apiVersion: placement.kubernetes-fleet.io/v1
kind: ClusterResourceSnapshot
metadata:
  ...
  labels:
    kubernetes-fleet.io/is-latest-snapshot: "true"
    kubernetes-fleet.io/parent-CRP: example-placement
    kubernetes-fleet.io/resource-index: "1"
  name: example-placement-1-snapshot
  ...
spec:
  selectedResources:
  - apiVersion: v1
    kind: Namespace
    metadata:
      labels:
        kubernetes.io/metadata.name: test-namespace
      name: test-namespace
    spec:
      finalizers:
      - kubernetes
  - apiVersion: v1
    data:
      key: value2
    kind: ConfigMap
    metadata:
      name: test-cm
      namespace: test-namespace

Using resource snapshots

Snapshots can be used as part of CRP staged rollouts managed via update runs as a rollback mechanism

Modifying the snapshot history limit

To change the number of items held in history, add a revisionHistoryLimit field to your CRP and provide an integer value. The default value is 10.

apiVersion: placement.kubernetes-fleet.io/v1
kind: ClusterResourcePlacement
metadata:
  name: crp-example
spec:
  revisionHistoryLimit: 20   # keep 20 items in history
  resourceSelectors:
    - group: ""
      kind: Namespace
      name: test-namespace
      version: v1
  policy:
    placementType: PickN
    numberOfClusters: 2
    affinity:
      clusterAffinity:
        requiredDuringSchedulingIgnoredDuringExecution:
          clusterSelectorTerms:
            - labelSelector:
                matchLabels:
                  fleet.azure.com/location: chinanorth3
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
      maxSurge: 50%

Next steps