RFC: Cargo replication

[leon3s]

Could be nice to brainstorm about how we can define a cargo replication.

We should be able to :

• run only one instance on all nodes
• run only one instance on targeted nodes
• run one instance in one node
• run x defined instances in all node
• run x defined instances in targeted nodes
• run x defined instances in one node
• autoscale on all nodes
• autoscale on targeted nodes
• autoscale on one node

What else we should be able to do ?
And how we define the data ?

Example of the enum that came in my mind:

/// Auto is used to automatically define that the number of replicas in the cluster
/// Number is used to manually set the number of replicas
/// Note: auto will ensure at least 1 replica exists in the cluster
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[cfg_attr(feature = "serde", serde(rename_all = "PascalCase"))]
#[cfg_attr(feature = "dev", derive(ToSchema))]
pub enum ReplicationMode {
  /// Auto is used to automatically define that the number of replicas in the cluster
  /// This will ensure at least 1 replica exists in the cluster
  /// And automatically add more replicas in the cluster if needed for redundancy
  Auto,
  /// Unique is used to ensure that only one replica exists in the cluster
  Unique,
  /// UniqueByNode is used to ensure one replica is running on each node
  UniqueByNode,
  /// UniqueByNodeGroups is used to ensure one replica is running on each node group
  UniqueByNodeGroups { groups: Vec<String> },
  /// UniqueByNodeNames is used to ensure one replica is running on each node name
  UniqueByNodeNames { names: Vec<String> },
  /// Number is used to manually set the number of replicas in one node
  Number(i64),
  /// NumberByNodes is used to manually set the number of replicas in each node
  NumberByNodes(i64),
  /// NumberByNodeGroups is used to manually set the number of replicas in each node group
  NumberByNodeGroups { groups: Vec<String>, number: i64 },
  /// NumberByNodeNames is used to manually set the number of replicas in each node name
  NumberByNodeNames { names: Vec<String>, number: i64 },
}