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Karmada (Kubernetes Armada) is a Kubernetes management system that enables cloud-native applications to run across multiple Kubernetes clusters and clouds with no changes to the underlying applications. By speaking Kubernetes-native APIs and providing advanced scheduling capabilities, Karmada truly enables multi-cloud Kubernetes environment. It aims to provide turnkey automation for multi-cluster application management in multi-cloud and hybrid cloud scenarios with key features such as centralized multi-cloud management, high availability, failure recovery, and traffic scheduling.

API2: "Federated Multi-Access Edge Cloud Platform" blueprint specific APIs 

// Cluster represents the desire state and status of a member cluster.
type Cluster struct {
metav1.TypeMeta `json:",inline"`
metav1.ObjectMeta `json:"metadata,omitempty"`

// Spec represents the specification of the desired behavior of member cluster.
Spec ClusterSpec `json:"spec"`

// Status represents the status of member cluster.
// +optional
Status ClusterStatus `json:"status,omitempty"`
}

// ClusterSpec defines the desired state of a member cluster.
type ClusterSpec struct {
// SyncMode describes how a cluster sync resources from karmada control plane.
// +kubebuilder:validation:Enum=Push;Pull
// +required
SyncMode ClusterSyncMode `json:"syncMode"`

// The API endpoint of the member cluster. This can be a hostname,
// hostname:port, IP or IP:port.
// +optional
APIEndpoint string `json:"apiEndpoint,omitempty"`

// SecretRef represents the secret contains mandatory credentials to access the member cluster.
// The secret should hold credentials as follows:
// - secret.data.token
// - secret.data.caBundle
// +optional
SecretRef *LocalSecretReference `json:"secretRef,omitempty"`

// InsecureSkipTLSVerification indicates that the karmada control plane should not confirm the validity of the serving
// certificate of the cluster it is connecting to. This will make the HTTPS connection between the karmada control
// plane and the member cluster insecure.
// Defaults to false.
// +optional
InsecureSkipTLSVerification bool `json:"insecureSkipTLSVerification,omitempty"`

// ProxyURL is the proxy URL for the cluster.
// If not empty, the karmada control plane will use this proxy to talk to the cluster.
// More details please refer to: https://github.com/kubernetes/client-go/issues/351
// +optional
ProxyURL string `json:"proxyURL,omitempty"`

// Provider represents the cloud provider name of the member cluster.
// +optional
Provider string `json:"provider,omitempty"`

// Region represents the region of the member cluster locate in.
// +optional
Region string `json:"region,omitempty"`

// Zone represents the zone of the member cluster locate in.
// +optional
Zone string `json:"zone,omitempty"`

// Taints attached to the member cluster.
// Taints on the cluster have the "effect" on
// any resource that does not tolerate the Taint.
// +optional
Taints []corev1.Taint `json:"taints,omitempty"`
}

// ClusterStatus contains information about the current status of a
// cluster updated periodically by cluster controller.
type ClusterStatus struct {
// KubernetesVersion represents version of the member cluster.
// +optional
KubernetesVersion string `json:"kubernetesVersion,omitempty"`

// APIEnablements represents the list of APIs installed in the member cluster.
// +optional
APIEnablements []APIEnablement `json:"apiEnablements,omitempty"`

// Conditions is an array of current cluster conditions.
// +optional
Conditions []metav1.Condition `json:"conditions,omitempty"`

// NodeSummary represents the summary of nodes status in the member cluster.
// +optional
NodeSummary *NodeSummary `json:"nodeSummary,omitempty"`

// ResourceSummary represents the summary of resources in the member cluster.
// +optional
ResourceSummary *ResourceSummary `json:"resourceSummary,omitempty"`
}

// ResourceSummary represents the summary of resources in the member cluster.
type ResourceSummary struct {
// Allocatable represents the resources of a cluster that are available for scheduling.
// Total amount of allocatable resources on all nodes.
// +optional
Allocatable corev1.ResourceList `json:"allocatable,omitempty"`
// Allocating represents the resources of a cluster that are pending for scheduling.
// Total amount of required resources of all Pods that are waiting for scheduling.
// +optional
Allocating corev1.ResourceList `json:"allocating,omitempty"`
// Allocated represents the resources of a cluster that have been scheduled.
// Total amount of required resources of all Pods that have been scheduled to nodes.
// +optional
Allocated corev1.ResourceList `json:"allocated,omitempty"`
}

// ClusterList contains a list of member cluster
type ClusterList struct {
metav1.TypeMeta `json:",inline"`
metav1.ListMeta `json:"metadata,omitempty"`

// Items holds a list of Cluster.
Items []Cluster `json:"items"`
}

// PropagationPolicy represents the policy that propagates a group of resources to one or more clusters.
type PropagationPolicy struct {
metav1.TypeMeta `json:",inline"`
metav1.ObjectMeta `json:"metadata,omitempty"`

// Spec represents the desired behavior of PropagationPolicy.
// +required
Spec PropagationSpec `json:"spec"`
}

// PropagationSpec represents the desired behavior of PropagationPolicy.
type PropagationSpec struct {
// ResourceSelectors used to select resources.
// +required
ResourceSelectors []ResourceSelector `json:"resourceSelectors"`

// Association tells if relevant resources should be selected automatically.
// e.g. a ConfigMap referred by a Deployment.
// default false.
// +optional
Association bool `json:"association,omitempty"`

// Placement represents the rule for select clusters to propagate resources.
// +optional
Placement Placement `json:"placement,omitempty"`

// DependentOverrides represents the list of overrides(OverridePolicy)
// which must present before the current PropagationPolicy takes effect.
//
// It used to explicitly specify overrides which current PropagationPolicy rely on.
// A typical scenario is the users create OverridePolicy(ies) and resources at the same time,
// they want to ensure the new-created policies would be adopted.
//
// Note: For the overrides, OverridePolicy(ies) in current namespace and ClusterOverridePolicy(ies),
// which not present in this list will still be applied if they matches the resources.
// +optional
DependentOverrides []string `json:"dependentOverrides,omitempty"`

// SchedulerName represents which scheduler to proceed the scheduling.
// If specified, the policy will be dispatched by specified scheduler.
// If not specified, the policy will be dispatched by default scheduler.
// +optional
SchedulerName string `json:"schedulerName,omitempty"`
}

// ResourceSelector the resources will be selected.
type ResourceSelector struct {
// APIVersion represents the API version of the target resources.
// +required
APIVersion string `json:"apiVersion"`

// Kind represents the Kind of the target resources.
// +required
Kind string `json:"kind"`

// Namespace of the target resource.
// Default is empty, which means inherit from the parent object scope.
// +optional
Namespace string `json:"namespace,omitempty"`

// Name of the target resource.
// Default is empty, which means selecting all resources.
// +optional
Name string `json:"name,omitempty"`

// A label query over a set of resources.
// If name is not empty, labelSelector will be ignored.
// +optional
LabelSelector *metav1.LabelSelector `json:"labelSelector,omitempty"`
}

// FieldSelector is a field filter.
type FieldSelector struct {
// A list of field selector requirements.
MatchExpressions []corev1.NodeSelectorRequirement `json:"matchExpressions,omitempty"`
}

// Placement represents the rule for select clusters.
type Placement struct {
// ClusterAffinity represents scheduling restrictions to a certain set of clusters.
// If not set, any cluster can be scheduling candidate.
// +optional
ClusterAffinity *ClusterAffinity `json:"clusterAffinity,omitempty"`

// ClusterTolerations represents the tolerations.
// +optional
ClusterTolerations []corev1.Toleration `json:"clusterTolerations,omitempty"`

// SpreadConstraints represents a list of the scheduling constraints.
// +optional
SpreadConstraints []SpreadConstraint `json:"spreadConstraints,omitempty"`

// ReplicaScheduling represents the scheduling policy on dealing with the number of replicas
// when propagating resources that have replicas in spec (e.g. deployments, statefulsets) to member clusters.
// +optional
ReplicaScheduling *ReplicaSchedulingStrategy `json:"replicaScheduling,omitempty"`
}

// SpreadFieldValue is the type to define valid values for SpreadConstraint.SpreadByField
type SpreadFieldValue string

// Available fields for spreading are: cluster, region, zone, and provider.
const (
SpreadByFieldCluster SpreadFieldValue = "cluster"
SpreadByFieldRegion SpreadFieldValue = "region"
SpreadByFieldZone SpreadFieldValue = "zone"
SpreadByFieldProvider SpreadFieldValue = "provider"
)

// SpreadConstraint represents the spread constraints on resources.
type SpreadConstraint struct {
// SpreadByField represents the fields on Karmada cluster API used for
// dynamically grouping member clusters into different groups.
// Resources will be spread among different cluster groups.
// Available fields for spreading are: cluster, region, zone, and provider.
// SpreadByField should not co-exist with SpreadByLabel.
// If both SpreadByField and SpreadByLabel are empty, SpreadByField will be set to "cluster" by system.
// +kubebuilder:validation:Enum=cluster;region;zone;provider
// +optional
SpreadByField SpreadFieldValue `json:"spreadByField,omitempty"`

// SpreadByLabel represents the label key used for
// grouping member clusters into different groups.
// Resources will be spread among different cluster groups.
// SpreadByLabel should not co-exist with SpreadByField.
// +optional
SpreadByLabel string `json:"spreadByLabel,omitempty"`

// MaxGroups restricts the maximum number of cluster groups to be selected.
// +optional
MaxGroups int `json:"maxGroups,omitempty"`

// MinGroups restricts the minimum number of cluster groups to be selected.
// Defaults to 1.
// +optional
MinGroups int `json:"minGroups,omitempty"`
}

// ClusterAffinity represents the filter to select clusters.
type ClusterAffinity struct {
// LabelSelector is a filter to select member clusters by labels.
// If non-nil and non-empty, only the clusters match this filter will be selected.
// +optional
LabelSelector *metav1.LabelSelector `json:"labelSelector,omitempty"`

// FieldSelector is a filter to select member clusters by fields.
// If non-nil and non-empty, only the clusters match this filter will be selected.
// +optional
FieldSelector *FieldSelector `json:"fieldSelector,omitempty"`

// ClusterNames is the list of clusters to be selected.
// +optional
ClusterNames []string `json:"clusterNames,omitempty"`

// ExcludedClusters is the list of clusters to be ignored.
// +optional
ExcludeClusters []string `json:"exclude,omitempty"`
}

// ReplicaSchedulingType describes scheduling methods for the "replicas" in a resouce.
type ReplicaSchedulingType string

const (
// ReplicaSchedulingTypeDuplicated means when propagating a resource,
// each candidate member cluster will directly apply the original replicas.
ReplicaSchedulingTypeDuplicated ReplicaSchedulingType = "Duplicated"
// ReplicaSchedulingTypeDivided means when propagating a resource,
// each candidate member cluster will get only a part of original replicas.
ReplicaSchedulingTypeDivided ReplicaSchedulingType = "Divided"
)

// ReplicaDivisionPreference describes options of how replicas can be scheduled.
type ReplicaDivisionPreference string

const (
// ReplicaDivisionPreferenceAggregated divides replicas into clusters as few as possible,
// while respecting clusters' resource availabilities during the division.
ReplicaDivisionPreferenceAggregated ReplicaDivisionPreference = "Aggregated"
// ReplicaDivisionPreferenceWeighted divides replicas by weight according to WeightPreference.
ReplicaDivisionPreferenceWeighted ReplicaDivisionPreference = "Weighted"
)

// ReplicaSchedulingStrategy represents the assignment strategy of replicas.
type ReplicaSchedulingStrategy struct {
// ReplicaSchedulingType determines how the replicas is scheduled when karmada propagating
// a resource. Valid options are Duplicated and Divided.
// "Duplicated" duplicates the same replicas to each candidate member cluster from resource.
// "Divided" divides replicas into parts according to number of valid candidate member
// clusters, and exact replicas for each cluster are determined by ReplicaDivisionPreference.
// +kubebuilder:validation:Enum=Duplicated;Divided
// +optional
ReplicaSchedulingType ReplicaSchedulingType `json:"replicaSchedulingType,omitempty"`

// ReplicaDivisionPreference determines how the replicas is divided
// when ReplicaSchedulingType is "Divided". Valid options are Aggregated and Weighted.
// "Aggregated" divides replicas into clusters as few as possible,
// while respecting clusters' resource availabilities during the division.
// "Weighted" divides replicas by weight according to WeightPreference.
// +kubebuilder:validation:Enum=Aggregated;Weighted
// +optional
ReplicaDivisionPreference ReplicaDivisionPreference `json:"replicaDivisionPreference,omitempty"`

// WeightPreference describes weight for each cluster or for each group of cluster
// If ReplicaDivisionPreference is set to "Weighted", and WeightPreference is not set, scheduler will weight all clusters the same.
// +optional
WeightPreference *ClusterPreferences `json:"weightPreference,omitempty"`
}

// PropagationPolicyList contains a list of PropagationPolicy.
type PropagationPolicyList struct {
metav1.TypeMeta `json:",inline"`
metav1.ListMeta `json:"metadata,omitempty"`
Items []PropagationPolicy `json:"items"`
}

// ClusterPropagationPolicy represents the cluster-wide policy that propagates a group of resources to one or more clusters.
// Different with PropagationPolicy that could only propagate resources in its own namespace, ClusterPropagationPolicy
// is able to propagate cluster level resources and resources in any namespace other than system reserved ones.
// System reserved namespaces are: karmada-system, karmada-cluster, karmada-es-*.
type ClusterPropagationPolicy struct {
metav1.TypeMeta `json:",inline"`
metav1.ObjectMeta `json:"metadata,omitempty"`

// Spec represents the desired behavior of ClusterPropagationPolicy.
// +required
Spec PropagationSpec `json:"spec"`
}

// ClusterPropagationPolicyList contains a list of ClusterPropagationPolicy.
type ClusterPropagationPolicyList struct {
metav1.TypeMeta `json:",inline"`
metav1.ListMeta `json:"metadata,omitempty"`
Items []ClusterPropagationPolicy `json:"items"`
}"Federated Multi-Access Edge Cloud Platform" blueprint specific APIs would be designed and built out as part of the future Akraino releases. Currently, the blueprint publishes APIs related to open source Karmada project only.