IRealmPlacement

Remarks

ADR-019. Three backends — Kubernetes, Docker, Process — probed in that order at startup, with the first that answers winning and configuration able to override. The interface is small on purpose: everything above it reasons about shards, and the only thing it needs from the world below is that a process with a given RealmSpec exists, can be told to stop, and can be watched.

⚠ Nothing here is on a frame path, which is why every method is asynchronous without apology. Starting a pod is seconds; ADR-016's rule about never awaiting the control plane from a tick is what keeps that acceptable.

Placement.Process is to this document what Vixen.Net.Transport.Local is to doc 16 — the backend that makes the whole system an ordinary unit test rather than an integration environment. A test that needs eight realms starts eight processes on a laptop, deterministically, and asserts against the same interface production uses.

Methods (5)

• ValueTask<PlacementProbe> ProbeAsync(CancellationToken cancellation)

  Whether this backend can run here, and what it found.

• ValueTask<RealmInstance> StartAsync(RealmSpec spec, CancellationToken cancellation)

  Brings a realm up.

• ValueTask StopAsync(RealmInstanceId instance, StopMode mode, CancellationToken cancellation)

  Takes a realm down.

• ValueTask<IReadOnlyList<RealmInstance>> ListAsync(CancellationToken cancellation)

  What this backend believes is running.

• IAsyncEnumerable<PlacementEvent> WatchAsync(CancellationToken cancellation)

  Everything that happens to instances, as it happens.

Used by (6)

• DockerPlacementVixen.Live.Placement.Docker
• KubernetesPlacementVixen.Live.Placement.Kubernetes
• MapGrainVixen.Live.Orchestrator
• MapOptionsVixen.Live.Orchestrator
• PlacementWatchVixen.Live.Placement.Docker.Tests
• ProcessPlacementVixen.Live.Placement.Process