rustfs/docs/architecture/ecstore-module-split-plan.md

ECStore Module Split Plan

This plan records the remaining ECStore split work after the final audit remediation pass. It is intentionally design-only: no crate movement should start until each candidate boundary has explicit contracts, compatibility coverage, dependency evidence, and rollback steps.

Current Shape

Area	Current owner	Size	Split status
Bucket lifecycle	crates/ecstore/src/bucket/lifecycle/	8,657 lines	Proposal only
Bucket replication	crates/ecstore/src/bucket/replication/	8,730 lines	Proposal only
Set disks	crates/ecstore/src/set_disk/	state carrier plus operation modules	Keep in ECStore
Public ECStore facade	crates/ecstore/src/api/mod.rs	broad compatibility surface	Shrink only through guarded PRs

The file split inside set_disk/ is already operation-oriented: read, write, list, multipart, lock, heal, and replication code live in separate modules. The remaining large surface is the shared SetDisks state and cross-cutting contracts, not only file layout.

Non-Negotiable Rules

• Do not split crates in the same PR that moves runtime state or changes startup behavior.
• Do not change object placement, quorum, reader semantics, lifecycle queues, replication queues, notification dispatch, audit events, or scanner repair behavior during inventory and contract PRs.
• Do not expose new direct ECStore internals to outer crates; use the existing storage-api and owner-local facade boundaries.
• Keep rustfs_ecstore::api compatibility visible until each consumer path has compile coverage and an explicit replacement.

SetDisks Split Direction

Do not replace SetDisks with several runtime structs in one change. The safe path is:

1. Keep SetDisks as the shared state carrier while operation modules continue to own read/write/list/multipart/lock/heal/replication behavior.
2. Extract pure contracts first: shard source, disk error, bitrot IO, namespace lock, metrics labels, and file metadata access.
3. Move one operation family only after its contracts are covered by focused tests and the facade compatibility path is explicit.
4. Preserve the old rustfs_ecstore::api::set_disk surface until downstream compatibility tests prove no caller depends on removed names.

The first executable SetDisks follow-up should be an inventory or guardrail PR, not a runtime split PR.

Lifecycle Candidate

bucket/lifecycle is not ready for a standalone crate yet.

Current coupling:

• lifecycle workers and transition state read ECStore runtime sources for object-store handles, expiry state, transition state, tier config, deployment IDs, and local node names;
• stale multipart cleanup depends on SetDisks internals and bucket metadata through the lifecycle metadata boundary;
• lifecycle expiry schedules bucket replication delete work through the replication lifecycle bridge contract;
• lifecycle evaluation shares S3 DTOs, object metadata, object lock, replication config reads through lifecycle-local boundaries, scanner metrics, notification/audit side effects, and tier services.

Required contracts before crate movement:

• LifecycleObjectStore: object stat, delete, transition, restore, multipart cleanup, and version-aware metadata operations needed by lifecycle workers.
• LifecycleMetadataStore: lifecycle, object-lock, replication, bucket versioning, and stale multipart metadata lookups without importing ECStore implementation modules. Current lifecycle config reads are concentrated in crates/ecstore/src/bucket/lifecycle/metadata_boundary.rs.
• LifecycleRuntime: expiry state, transition state, tier config, deployment ID, local node name, queue metrics, cancellation, and worker sizing.
• LifecycleReplicationSink: schedule lifecycle-originated replication deletes without depending on the replication implementation module.
• LifecycleAuditSink: lifecycle audit and notification emission boundary.

First safe PR:

• add a lifecycle extraction inventory section or module-level README;
• list current ECStore/runtime dependencies and the target contract owner for each dependency;
• add no code movement and no behavior changes.

The module-level inventory lives in crates/ecstore/src/bucket/lifecycle/README.md.

Focused verification for the first code-bearing lifecycle PR:

• cargo test -p rustfs-ecstore lifecycle --lib
• cargo check -p rustfs-ecstore --tests
• ./scripts/check_architecture_migration_rules.sh
• git diff --check

Replication Candidate

rustfs-replication now owns the resync status contracts and persisted resync status wire format. The remaining bucket/replication worker runtime is not ready for a full standalone crate yet.

Current coupling:

• replication workers depend on ReplicationStorage, ECStore object APIs and owner storage-api contracts through the replication storage boundary, bucket target clients, bucket metadata, file metadata replication state through the filemeta boundary, config-derived storage class labels through the config store, scanner repair classification, runtime replication pool/stat handles, bucket monitor and bandwidth reader access through local boundaries, local node names, and notification events;
• resync and delete replication paths call metadata paths through the metadata boundary, while bucket target system access, target config types, and target operation types are concentrated behind the replication target boundary;
• lifecycle delete paths schedule replication work through ReplicationLifecycleBridge, while scanner heal paths schedule replication work through ReplicationScannerBridge, and app/SetDisks object write/delete paths use ReplicationObjectBridge;
• bucket metadata migration and bucket target removal checks use local replication bridges instead of importing resyncer codec or config helper internals;
• resync options, bucket/target resync status DTOs, status display labels, and the persisted resync status wire format live in crates/replication, with ECStore retaining only error mapping and MRF persistence locally;
• ReplicationCrateFileMetaIndependence: replication status, decision, MRF, resync, and target-reset wire contracts are owned inside rustfs-replication instead of importing rustfs-filemeta;
• ReplicationCrateStorageApiIndependence: delete work DTOs are owned inside rustfs-replication; ECStore converts storage-api delete DTOs at the replication storage boundary instead of rustfs-replication importing rustfs-storage-api;
• direct ECStore replication imports from rustfs-replication are limited to *_boundary.rs modules;
• storage-api delete replication status/state helpers use the local crates/storage-api/src/replication.rs contract boundary; ECStore converts those owner DTOs at the replication storage boundary before queueing work;
• admin replication extension target filtering and resync request construction stay behind the admin storage boundary instead of exposing replication work DTO construction to handlers;
• scanner, admin, storage-owner, and app storage replication status/DTO/helper consumers import those contracts through the ECStore replication facade;
• app object and multipart writes call object-replication boundary helpers instead of constructing replication work DTOs or choosing object replication operation types at the use-case layer;
• RustFS runtime consumers receive replication pool/stat handles through storage-owner wrapper types instead of carrying ECStore replication handles through app, admin, startup, or workload-admission layers;
• global replication pool/stat initialization still lives with ECStore runtime compatibility state;
• modules inside bucket/replication use local relative paths rather than the ECStore owner path for replication self-imports;
• replication runtime source access uses storage/bandwidth boundary aliases for ECStore object store and bucket monitor implementation types;
• the ECStore replication facade in mod.rs uses explicit compatibility exports instead of wildcard re-exports from implementation modules.

Required contracts before crate movement:

• ReplicationObjectIO: object read/write primitives for config, MRF, resync status, and multipart replication paths. ECStore object API reader/writer types and storage-api object IO contracts are concentrated in crates/ecstore/src/bucket/replication/replication_storage_boundary.rs.
• ReplicationStorage: keep the existing trait as the starting point, then split object read/write/delete, walk, and metadata update responsibilities only when call sites prove a narrower shape. ECStore object API, storage-api contracts, and read option types are concentrated in crates/ecstore/src/bucket/replication/replication_storage_boundary.rs.
• ReplicationMetadataStore: replication config, target reset headers, MRF/resync state, and status persistence. Metadata sys access and replication metadata path constants are exposed through the contract type in crates/ecstore/src/bucket/replication/replication_metadata_boundary.rs.
• ReplicationConfigStore: replication config persistence and config-derived labels used by target options. Config read/save helpers and storage class labels are exposed through the contract type in crates/ecstore/src/bucket/replication/replication_config_store.rs.
• ReplicationFileMeta: replication status, decisions, MRF entries, resync decisions, and target reset helpers. ECStore concentrates filemeta-to- replication compatibility conversions in crates/ecstore/src/bucket/replication/replication_filemeta_boundary.rs, while FileInfo remains in the storage boundary for storage trait bindings and walk options.
• ReplicationCrateFileMetaIndependence: filemeta wire contracts consumed by replication workers are owned in crates/replication/src/filemeta.rs, and rustfs-replication must not import or depend on rustfs-filemeta.
• ReplicationCrateStorageApiIndependence: delete work DTOs consumed by replication delete/queue/operation helpers are owned in crates/replication/src/storage_api.rs, and rustfs-replication must not import or depend on rustfs-storage-api.
• EcstoreReplicationBoundaryImports: ECStore-side imports from rustfs-replication are concentrated in replication *_boundary.rs modules.
• RuntimeReplicationFacadeConsumers: scanner, admin, storage-owner, and app storage replication status/DTO/helper consumers import through rustfs-ecstore; runtime code under rustfs/src does not import rustfs-replication directly, and the RustFS runtime/scanner crates do not depend on it.
• StorageApiReplicationContracts: owner-facing storage-api delete DTO replication state/status helpers remain concentrated in crates/storage-api/src/replication.rs, while replication worker DTOs live in rustfs-replication.
• ReplicationErrorBoundary: ECStore error/result contracts and replication-specific error classifiers. crate::error imports are concentrated in crates/ecstore/src/bucket/replication/replication_error_boundary.rs.
• ReplicationTargetStore: bucket target listing, target client lookup, target offline checks, target config types, and target operation option types. Bucket target sys access, BucketTargets, and target operation types are exposed through the contract type in crates/ecstore/src/bucket/replication/replication_target_boundary.rs.
• ReplicationRuntime: pool, stats, worker admission, bucket monitor, local node identity, cancellation, and queue sizing. Concrete ECStore object store and bucket monitor types stay behind local storage/bandwidth boundaries.
• ReplicationBandwidthLimiter: target reader wrapping for replication bandwidth accounting and throttling.
• ReplicationVersioningStore, ReplicationLockTiming, ReplicationMsgpCodec, and ReplicationTagFilter: smaller state/codec/filter contracts that keep bucket versioning, SetDisks lock timing, MessagePack helpers, and bucket tagging helper access behind local replication boundary types.
• ReplicationEventSink: notification/audit events for skipped, failed, and completed replication operations, including local event host selection.
• ReplicationLifecycleBridge: lifecycle-originated delete and version-purge scheduling is exposed through the contract type in crates/ecstore/src/bucket/replication/replication_lifecycle_bridge.rs.
• ReplicationMigrationBridge: persisted resync status decode/encode access for bucket metadata migration is exposed through the contract type in crates/ecstore/src/bucket/replication/replication_migration_bridge.rs.
• ReplicationResyncContracts: resync options, target/bucket resync status, status labels, and persisted status encoding live in crates/replication.
• ReplicationObjectBridge: app and SetDisks object write/delete replication decisions and scheduling are exposed through the contract type in crates/ecstore/src/bucket/replication/replication_object_bridge.rs.
• ObsReplicationStatsSnapshot: observability reads replication bucket/site metrics through obs-local snapshot DTOs in crates/obs/src/metrics/storage_api.rs instead of carrying the ECStore replication stats handle through collectors.
• StorageReplicationPoolHandle / StorageReplicationStatsHandle: RustFS app, admin, startup, and workload-admission code use storage-owner wrapper types from rustfs/src/storage/storage_api.rs for pool activity, resync, queue counts, proxy stats, and site metrics snapshots.
• ReplicationScannerBridge: scanner-originated replication heal scheduling is exposed through the contract type in crates/ecstore/src/bucket/replication/replication_scanner_bridge.rs. Scanner consumers receive scanner-local replication config/admission/heal object DTOs from crates/scanner/src/storage_api.rs instead of constructing or inspecting replication queue DTOs directly.
• ReplicationTargetConfigBridge: bucket target removal checks against replication target rules are exposed through the contract type in crates/ecstore/src/bucket/replication/replication_target_config_bridge.rs.
• ReplicationFacade: the current rustfs_ecstore::api::bucket::replication compatibility surface is an explicit symbol list guarded against wildcard re-exports while downstream owners migrate to narrower contracts.

First safe PR:

• add a replication extraction inventory section or module-level README;
• list current ECStore/runtime dependencies and the target contract owner for each dependency;
• keep global pool/stat initialization and queue behavior unchanged.

The module-level inventory lives in crates/ecstore/src/bucket/replication/README.md.

Focused verification for the first code-bearing replication PR:

• cargo test -p rustfs-ecstore replication --lib
• cargo check -p rustfs-ecstore --tests
• ./scripts/check_architecture_migration_rules.sh
• git diff --check

Facade Shrink Plan

The broad rustfs_ecstore::api facade remains a compatibility boundary, not a new architecture target. The current facade groups and external consumers are recorded in ecstore-api-facade-inventory.md. Shrinking it must be monotonic:

1. Inventory every public facade group and consumer.
2. Add compile-time coverage before removing or narrowing a facade item.
3. Move outer consumers to storage-api or owner-local compatibility boundaries.
4. Remove one facade group per PR only after downstream compatibility tests pass.

Do not delete facade groups only because the underlying module moved. Keep the facade stable until the replacement path is visible and tested.

Ready-To-Split Checklist

A candidate split is ready for code movement only when all items below are true:

• dependency graph shows no cycle with ECStore, storage-api, runtime sources, or owner-local compatibility modules;
• contract traits compile without importing ECStore implementation modules;
• old facade names have compatibility tests or explicit deprecation coverage;
• focused tests cover the changed owner path before any full gate is attempted;
• rollback preserves object IO, quorum, lifecycle/replication queues, scanner repair, notification/audit events, and metadata compatibility.