Clusters unique per cluster

🟡 Intermediate · Lesson 25

Clusters - named groups of dynamic conduits that AUTO-SHARE cluster-scoped spells. unique_per_conduit_cluster finally comes alive: one instance per cluster, shared by every member. (This completes the declaration parked in the expert tier's example 01.)

Before you run

Use the Intermediate guide for prerequisite concepts. Run from a checkout with Melder installed and Python 3.14 free-threading selected. The collection download includes the level's local helper modules.

Run the saved script

python UX_and_AIX_experiences/02_intermediate/25_clusters_unique_per_cluster.py

py -3.14t UX_and_AIX_experiences/02_intermediate/25_clusters_unique_per_cluster.py

Download this collection · Source on GitHub

Public surface

create_cluster, add_conduit_to_cluster, existence="unique_per_conduit_cluster"

Code

"""
TIER: intermediate (25)
GOAL: Clusters - named groups of dynamic conduits that AUTO-SHARE
      cluster-scoped spells. unique_per_conduit_cluster finally comes
      alive: one instance per cluster, shared by every member. (This
      completes the declaration parked in the expert tier's example 01.)
SURFACE EXERCISED: create_cluster, add_conduit_to_cluster,
                   existence="unique_per_conduit_cluster"
"""
import sys
from pathlib import Path

sys.path.insert(0, str(Path(__file__).parent))  # local helper (see _dynamic_world)
from _dynamic_world import dynamic_spellbook

import melder as md


class ClusterBus:
    pass


def main() -> None:
    """Build a linked cluster and assert that its members resolve the same bus."""
    owner_book = dynamic_spellbook()
    # permissions="create" matters: cluster auto-sharing contracts the
    # spell to each joining member WITH the spell's own permissions.
    owner_book.bind(spell=ClusterBus,
                    existence="unique_per_conduit_cluster",
                    permissions="create")
    owner = owner_book.conjure(dynamic=True, name="cluster-owner")
    member = dynamic_spellbook().conjure(dynamic=True, name="cluster-member")

    # Contracts ride LINKS: the cluster auto-share adds spells into the
    # members' existing contracts, and the contract bucket is born at
    # link(). Unlinked members share NOTHING.
    owner.link(member)

    cloud = owner.get_conduit_cloud()
    cloud.create_cluster("workers")
    cloud.add_conduit_to_cluster(owner, "workers")

    # ELECT THE LEADER before more members join: the cluster's shared
    # store belongs to the elected leader, and joins auto-share against
    # the armed cluster - then the rest falls into place.
    cloud.get_cluster("workers").elect_leader(owner.id)

    cloud.add_conduit_to_cluster(member, "workers")

    bus_a = owner.meld(spell=ClusterBus)
    bus_b = member.meld(spell=ClusterBus)
    assert bus_a is bus_b, "cluster members must share the elected leader's bus"
    print("one bus per cluster, shared by members:", bus_a is bus_b)


if __name__ == "__main__":
    main()

Check the outcome

The script contains its own assertions or demonstrated refusal paths. Run it to evaluate those checks against your installed version. The code above is taken directly from the saved file; no run output is invented here.

More intermediate examples · Level guide