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import-cluster-resources.md

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[Beta] Import your real cluster's resources

There are two ways to import resources from your cluster. These methods cannot be used simultaneously.

  • Import resources from your cluster once when initializing the simulator.
  • Keep importing resources from your cluster.

One-shot import: Import resources once when initializing the simulator

To use this, you need to follow these two steps in the simulator configuration:

  • Set true to externalImportEnabled.
  • Set the path of the kubeconfig file for the your cluster to KubeConfig.
    • This feature only requires the read permission for resources.
externalImportEnabled: true
kubeConfig: "/path/to/your-cluster-kubeconfig"

Syncer: Keep importing resources

To use this, you need to follow these two steps in the scheduler configuration:

  • Set true to resourceSyncEnabled.
  • Set the path of the kubeconfig file for the your cluster to KubeConfig.
    • This feature only requires the read permission for resources.
resourceSyncEnabled: true
kubeConfig: "/path/to/your-cluster-kubeconfig"

Note

When you enable resourceSyncEnabled, adding/updating/deleting resources directly in the simulator cluster could cause a problem of syncing. You can do them for debugging etc purposes though, make sure you reboot the simulator and the fake source cluster afterward.

How it syncs Pods

We cannot simply sync all changes to Pods, because the real cluster has the scheduler, and it schedules all Pods in the cluster. If we simply synced all changes to Pods, the scheduling result would also be synced, and may conflicted with the decision of another scheduler which is in a fake cluster.

So, we don't sync any of updated events to scheduled Pods. Pods are synced like:

  1. In a real cluster, Pod-a is created
  2. In a fake cluster, Pod-a is created. (synced)
  3. In a real cluster, the scheduler schedules Pod-a to Node-a. We don't copy this change to a fake cluster.
  4. In a fake cluster, the scheduler, which is different one from (3), schedules Pod-a to Node-x.

It means that the scheduling results may be different between a real cluster and a fake cluster. But, it's OK. Our purpose is to create a fake cluster for testing the scheduling, which gets the same load as the production cluster.

Resources to import

It imports the following resources, which the scheduler's default plugins take into account during scheduling.

  • Pods
  • Nodes
  • PersistentVolumes
  • PersistentVolumeClaims
  • StorageClasses

If you need to, you can tweak which resources to import via the option in /simulator/cmd/simulator/simulator.go:

dic, err := di.NewDIContainer(..., syncer.Options{
	// GVRsToSync is a list of GroupVersionResource that will be synced.
	// If GVRsToSync is nil, defaultGVRs are used.
	GVRsToSync: []schema.GroupVersionResource{
    		{Group: "your-group", Version: "v1", Resource: "your-custom-resources"},
  	}

	// Actually, more options are available...
 
	// AdditionalMutatingFunctions is a list of mutating functions that users add.
	AdditionalMutatingFunctions:  map[schema.GroupVersionResource]MutatingFunction{...}
	// AdditionalFilteringFunctions is a list of filtering functions that users add.
	AdditionalFilteringFunctions: map[schema.GroupVersionResource]FilteringFunction{...}
})

Note

Right now, one-shot import cannot change which resources to import.