NewInstanceSelector creates an instance selector.

NewMapInstanceGroupIDFunc creates a simple lookup function for an instances group, which looks up the group ID for an instance by the instance ID.

NewMirroredCustomGroupSelector constructs a placement.InstanceSelector which assigns shardsets according to their group ID (provided by instanceToGroupID).

NewNonMirroredSelector constructs an instance selector which doesn't mirror traffic (no shardsets) and which takes into account existing shard placement and instance weight in order to choose instances.

NewPortMirroredSelector returns a placement.InstanceSelector which creates groups of instances by their port number and assigns a shardset to each group, taking isolation groups into account while creating groups.

InstanceGroupIDFunc maps an instance to its mirrored group.