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Drivers and runtime status

See the portable contracts, the tested Cloudflare internals, and what is still missing from a deployable runtime path.

The Astilba Cache kernel depends on small typed contracts. Runtime adapters can change without duplicating the cache semantics they host.

This page is for runtime authors and readers evaluating production readiness. Application developers can start with Core concepts and return here when choosing or implementing a backend.

Driver model

Section titled “Driver model”
Contract Role
Store Key/value I/O for local L1, shared L2, and replication-mirror objects.
Registry The authoritative record used for tag checks and soft or hard mutations.
Bus The live delivery path for ordered invalidation events, resets, and declared gaps.
Lock Optional cross-isolate exclusion with a monotone fence token.
Codec Value encoding plus a wire identity checked before decode.
Cdn Planned edge purge queue boundary; not wired today.
Clock, Rng Explicit time and randomness for portable, deterministic behavior.
store.ts
interface Store {
  get(key: string): Promise<StoreValue | undefined>
  set(
    key: string,
    value: string,
    options?: StoreWriteOptions,
  ): Promise<void>
  delete(key: string): Promise<void>
}

Classified writes use the structural StoreWriteError shape. throttled and unavailable failures may leave a successful fill at durable: false; too_large is permanent and propagates rather than truncating the value.

Runtime implementation status

Section titled “Runtime implementation status”
Surface Status Detail
Portable contracts and kernel Implemented in source The public types, read/fill path, invalidation rules, codecs, scopes, singleflight, and write classification are exercised by deterministic tests.
Cloudflare KV Store Internal preview The real KV-backed Store passes applicable conformance and workerd tests. It enforces the 25 MiB value limit and floors supplied write residency at 60 seconds.
Coordinator Durable Object Internal preview The DO journals Registry commands, coalesces flush alarms, writes delta batches and snapshots, advances one terminal pointer, and serves live Registry RPC checks.
DO Registry client Internal preview The thin RPC client passes the Registry contract against the Coordinator under workerd.
Replication reader Internal preview A suspect read can replay a contiguous delta sequence and fails closed on missing, corrupt, or non-contiguous data. The documented reader does not bridge a gap with a snapshot.
Replication poller Not implemented The documented snapshot has no periodic poller; resynchronization happens reactively on a suspect read.
Durable Object Bus Not implemented The transport contract exists, but the Coordinator intentionally drops broadcast effects because there are no production subscribers yet.
Memory, Redis, Lock, CDN, and framework adapters Not implemented or unsupported No supported package entry point or deployment guide exists for these paths.

Cloudflare availability boundary

Section titled “Cloudflare availability boundary”

The Cloudflare files are exercised against workerd bindings, but they are not exported through a supported package subpath. The integration worker is a test host, not a deployment template. Do not import adapter source files directly.

The Coordinator writes replication snapshots, but the documented reader does not consume them as a recovery bridge. The Coordinator also replays an append-only command journal and does not yet checkpoint and truncate it for long-lived production operation.

Still required for a complete Workers path

Section titled “Still required for a complete Workers path”
  • Production Bus delivery, reconnect, backpressure, and subscriber lifecycle
  • Supported Cloudflare package exports and deployment configuration
  • Periodic replication polling and a supported driver for its ticks
  • Coordinator journal checkpointing and truncation
  • Background refresh adoption, retry, and completion tracking
  • CDN purge queue and honest completion promises
  • Deployed measurements for platform consistency and caching assumptions
Section titled “Related”