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Understanding snapshots for Azure Kubernetes Fleet Manager resource placement

Applies to: ✔️ Fleet Manager with hub cluster

Fleet Manager keeps a history of the 10 most recently used placement scheduling policies, along with resource versions the placement selected. It holds these policy and resource versions as snapshot objects:

  • For ClusterResourcePlacement (CRP): ClusterSchedulingPolicySnapshot and ClusterResourceSnapshot (cluster-scoped)
  • For ResourcePlacement (RP): SchedulingPolicySnapshot and ResourceSnapshot (namespace-scoped)

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

Note

If you're not already familiar with Fleet Manager's resource placement:

How resource snapshots are created

Any change to resources covered by the scope of CRP or RP resource selector automatically triggers the creation of a new resource snapshot within 60 seconds.

Viewing resource snapshots

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

Viewing ClusterResourceSnapshot (for ClusterResourcePlacement)

For cluster-scoped placements that use ClusterResourcePlacement, view ClusterResourceSnapshot objects.

In this sample, we use an updated ConfigMap, which creates two snapshots.

kubectl get clusterresourcesnapshots --show-labels

You see two snapshots, and the most recent one is marked as the latest (kubernetes-fleet.io/is-latest-snapshot=true) and has 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

You can inspect the contents of the example-placement-1-snapshot object 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

Viewing ResourceSnapshot (for ResourcePlacement)

For namespace-scoped placements that use ResourcePlacement, view ResourceSnapshot objects within the namespace.

In this example, you have a ResourcePlacement in the my-app namespace with updated ConfigMaps, which creates two snapshots.

kubectl get resourcesnapshots -n my-app --show-labels

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

NAME                               GEN   AGE    LABELS
app-configs-rp-0-snapshot          1     15m    kubernetes-fleet.io/is-latest-snapshot=false,kubernetes-fleet.io/parent-CRP=app-configs-rp,kubernetes-fleet.io/resource-index=0
app-configs-rp-1-snapshot          1     1m3s   kubernetes-fleet.io/is-latest-snapshot=true,kubernetes-fleet.io/parent-CRP=app-configs-rp,kubernetes-fleet.io/resource-index=1

You can inspect the contents of the app-configs-rp-1-snapshot object as follows.

kubectl get resourcesnapshots app-configs-rp-1-snapshot -n my-app -o yaml

apiVersion: placement.kubernetes-fleet.io/v1
kind: ResourceSnapshot
metadata:
  ...
  labels:
    kubernetes-fleet.io/is-latest-snapshot: "true"
    kubernetes-fleet.io/parent-CRP: app-configs-rp
    kubernetes-fleet.io/resource-index: "1"
  name: app-configs-rp-1-snapshot
  namespace: my-app
  ...
spec:
  selectedResources:
  - apiVersion: v1
    data:
      config: updated-value
    kind: ConfigMap
    metadata:
      name: app-config
      namespace: my-app
      labels:
        app: my-application

Using resource snapshots

Use snapshots as part of staged rollouts that update runs manage. They also serve as a rollback mechanism. Both ClusterResourcePlacement and ResourcePlacement support staged rollouts with their respective snapshot types:

  • ClusterResourcePlacement uses ClusterResourceSnapshot objects with ClusterStagedUpdateRun.
  • ResourcePlacement uses ResourceSnapshot objects with StagedUpdateRun.

For details about how to implement staged rollouts for both resource placement types, see Staged rollout strategy.

Modifying the snapshot history limit

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

For ClusterResourcePlacement

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: westus
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
      maxSurge: 50%

For ResourcePlacement

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

Next steps

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