ROVolume

Package: flyteplugins.union.io

Immutable, versioned volume — PRD §Core Concepts.

Always mounts read-only. Obtain one by:

• calling RWVolume.commit on a writable working copy;
• reading run.outputs.<name> after a prior task returned an RWVolume (auto-committed at task return);
• passing an already-resolved Volume value through one of the Volume.empty / Volume.new flows once it’s been committed.

There is no commit method here — that’s intentional. The only path from RO back to a writable working copy is fork.

Parameters

class ROVolume(
    kind: typing.Literal['flyte.volume/v1'] = 'flyte.volume/v1',
    name: str,
    bucket: str,
    storage: typing.Literal['s3', 'gs', 'wasb'] = 's3',
    region: typing.Optional[str] = None,
    endpoint: typing.Optional[str] = None,
    index: typing.Optional[flyte.io._file.File] = None,
    metadata_store_type: typing.Optional[str] = None,
    block_size: typing.Optional[str] = None,
    report: typing.Optional[bool] = None,
    used_bytes: typing.Optional[int] = None,
    inode_count: typing.Optional[int] = None,
    index_bytes: typing.Optional[int] = None,
    message: typing.Optional[str] = None,
    produced_by: typing.Optional[flyteplugins.union.io._base_volume.ActionRef] = None,
    parent_produced_by: typing.Optional[flyteplugins.union.io._base_volume.ActionRef] = None,
    artifact: typing.Optional[flyteplugins.union.io._base_volume.VolumeArtifact] = None,
    published_artifact_version: typing.Optional[str] = None,
    last_published_artifact_name: typing.Optional[str] = None,
    last_published_artifact_version: typing.Optional[str] = None,
)

Create a new model by parsing and validating input data from keyword arguments.

Raises ValidationError if the input data cannot be validated to form a valid model.

self is explicitly positional-only to allow self as a field name.

Properties

Methods

commit()

def commit(
    mount_path: Optional[str] = None,
    meta_dir: Optional[str] = None,
    timeout: float = 60.0,
    message: Optional[str] = None,
) -> 'Volume'

Deprecated. Drain + unmount + publish, returning a new Volume.

Prefer the typed lifecycle: create an RWVolume (Volume.new / ROVolume.fork), use RWVolume.commit for a keep-alive snapshot, and let the type transformer call RWVolume.finalize automatically when you return an RWVolume from a task. This base-class method is retained as a thin wrapper so existing Volume callers keep working; it emits DeprecationWarning.

empty()

def empty(
    name: str,
    bucket: Optional[str] = None,
    storage: Optional[StorageBackend] = None,
    region: Optional[str] = None,
    endpoint: Optional[str] = None,
    metadata_store_type: Optional[str] = None,
) -> 'Volume'

Declare a brand-new volume. The first mount() call will bootstrap the namespace (the underlying client refuses to format over a non-empty bucket prefix).

If bucket is omitted, it is derived from the currently active task context as {raw_data_root}/{project}/{domain}/volumes — following Flyte’s own layout for offloaded data. Must be called from inside a task in that case.

Regardless of store type, mounting the returned Volume needs a FUSE-capable image and pod — the fuse3 apt package and flyte.PodTemplate().allow_fuse() — see mount for the full runtime requirements.

metadata_store_type controls the in-pod metadata backend. When omitted it resolves from $UNION_VOLUME_METADATA_STORE and otherwise defaults to "badger".

• "badger" (default) keeps the namespace in an embedded BadgerDB directory — daemon-less like SQLite but with the highest metadata throughput of the three (~5x SQLite creates, ~27x cold random stats at 1M files), published as a backup stream. Requires the forked client binary (checkpoint verbs and --slice-domain), which flyteplugins-union bundles; a writable mount needs a claimed writer-session domain (the default domain-claim path provides one).
• "sqlite" keeps the namespace in a local SQLite file — runs in-process, needs no extra package beyond fuse3, works on a stock juicefs binary, and supports fork.
• "redis" runs an in-process redis-server and persists the namespace as an RDB snapshot; additionally requires redis-server in the image (installed by with_high_throughput_volume_deps, which also sets $UNION_VOLUME_METADATA_STORE=redis). Now that the embedded Badger store is the high-throughput default, Redis is a legacy explicit choice.

The choice is baked into the Volume and travels with it through lineage; subsequent mounts of the same Volume must use the same store type (use migrate_metadata_store_type to change it).

storage is the JuiceFS object-store backend. When omitted it is inferred from the bucket URI scheme (s3:// → s3, gs:// → gs, abfs(s):// → wasb), so a GCS/Azure bucket — including the default one derived from raw_data_path — gets the right backend without the caller spelling it out.

region pins the object-store region onto the Volume (S3 only — it forms the endpoint host). When omitted it’s derived from the ambient AWS_REGION / AWS_DEFAULT_REGION at mount time; pass it to make the Volume self-describing so a cross-region remount doesn’t depend on the consumer’s env.

fork()

def fork(
    name: str,
    meta_dir: Optional[str] = None,
    timeout: float = 60.0,
    artifact: object = Ellipsis,
) -> 'RWVolume'

Branch this immutable into a new writable working copy.

PRD §Lifecycle: ROVolume.fork() → RWVolume. The new RWVolume shares chunk objects with self (copy-on- write) but is allocator-disjoint so both can write without colliding on shared keys.

from_locator()

def from_locator(
    locator: str,
) -> 'ROVolume'

Load a previously published volume version by its locator.

The inverse of locator: download the metadata object at locator (the full serialized Volume value) and reconstruct it as an immutable ROVolume — index, bucket, metadata_store_type, stats and lineage all recovered, so the result is mountable read-only (or fork-able to branch + write) without any other arguments. This is how you reference a specific volume version across runs: stash vol.locator somewhere, then Volume.from_locator it back later.

Reads only the metadata object; the index and chunks are fetched lazily by mount. Needs object-store credentials for locator but no active task context. Raises VolumeError if locator is empty.

get_artifact_metadata()

def get_artifact_metadata()

Artifact declaration for the declarative (returned-as-output) publish path — flyte-sdk’s output conversion calls this on every top-level task output exposing it and, when it returns metadata, emits a ProducedArtifact on the Outputs envelope; the backend registers the artifact atomically with the action record (no RPC from the task).

Returns None — no declaration — when this volume carries no artifact intent, or when this exact seal is already in the registry (it was published imperatively via publish_artifact=True; re-declaring it would duplicate the version and emit a self-parent).

The version is left to the literal’s content hash (version_from_content — the same identity hash an imperative publish defaults to), because for a still-mounted RWVolume the final seal doesn’t exist until the transformer auto-finalizes during conversion. For that same reason stats attrs reflect this handle’s last seal (or are absent on a fresh handle) rather than the final one; the registered value itself always carries the authoritative numbers.

migrate_metadata_store_type()

def migrate_metadata_store_type(
    new_metadata_store_type: str,
    meta_dir: Optional[str] = None,
    new_meta_dir: Optional[str] = None,
) -> 'Volume'

Re-host this Volume’s metadata on new_metadata_store_type without copying data chunks.

new_metadata_store_type must differ from the current store type. The full namespace is exported and re-imported into a fresh meta store pointing at the same bucket. Chunks are addressed by stable IDs that are preserved across the migration, so no chunk traffic is required.

The returned Volume has a fresh index (snapshot of the loaded meta store), parent_produced_by linking to the pre-migration version, the same bucket / storage / name, and the new metadata_store_type.

Intent is migration, not fork: the old store is meant to be retired. As a defense against accidental concurrent use, the loaded store’s chunk-slice / inode / session counters are advanced by a random offset (same mechanism as fork) so that even if the old store is still mounted somewhere, its writes can’t collide with the migrated store’s writes in shared object-store keys.

Does not require a FUSE mount on either side. Safe to call from any task pod running the Volume runtime (Redis tooling is only needed if one of the stores is "redis").

model_post_init()

def model_post_init(
    context: Any,
)

This function is meant to behave like a BaseModel method to initialize private attributes.

It takes context as an argument since that’s what pydantic-core passes when calling it.

mount()

def mount(
    mount_path: Optional[str] = None,
    meta_dir: Optional[str] = None,
    cache_dir: Optional[str] = None,
    timeout: float = 120.0,
    attr_cache: float = 60.0,
    entry_cache: float = 60.0,
    dir_entry_cache: float = 60.0,
    shared_node_cache: Optional[bool] = None,
    cache_size_mb: Optional[int] = None,
    enable_xattr: bool = False,
) -> Path

Mount this volume read-only at mount_path and return the path.

Unset paths default to this volume’s name-keyed locations (see Volume.mount). read_only is intentionally absent from the signature — an ROVolume is statically un-writable, so the writeback / upload-delay knobs that only make sense for write-paths are omitted too.

shared_node_cache matters more here than on the base class: Volume.mount only ever shares for read-only mounts, so an ROVolume is what actually uses a node-shared chunk cache – automatically when the pod exposes one. cache_size_mb caps this mount’s on-disk cache. enable_xattr exposes extended attributes (needed when the mount is an overlayfs lower layer). See Volume.mount for all three. passthrough is absent: a read-only mount never uses the passthrough write path.

new()

def new(
    name: Optional[str] = None,
    bucket: Optional[str] = None,
    storage: Optional[StorageBackend] = None,
    region: Optional[str] = None,
    endpoint: Optional[str] = None,
    metadata_store_type: Optional[str] = None,
    artifact: Union[bool, str, 'ArtifactMetadata', 'VolumeArtifact', None] = None,
) -> 'RWVolume'

PRD §Lifecycle: create a fresh empty RWVolume.

Equivalent in mechanics to empty, but:

• name is optional (auto-generated when omitted, matching the PRD’s flyte.Volume.new(name=None) signature).
• Returns the strictly-typed RWVolume rather than the generic Volume, so mypy / pyright can enforce a task’s RO/RW contract at the signature boundary.

Prefer new in new code; empty is retained for existing callers that already declare -> Volume.

Creating the handle does no I/O; the first mount formats the namespace and needs a FUSE-capable image + pod (fuse3 and allow_fuse() — see mount).

artifact declares the volume’s artifact-registry identity (see VolumeArtifact for what identity does and doesn’t control):

• True — publish under the volume’s own name;
• a string — publish under that artifact name;
• a flyte.artifacts.Metadata (or VolumeArtifact) — full identity: name, description, attrs;
• None (default) — no standing identity.

recover_mount()

def recover_mount(
    timeout: float = 120.0,
) -> Path

Remount this volume after its mount daemon died under it.

The case: the client process is gone (crashed, or torn down without a successor) and its FUSE connection was aborted — by the broker’s auto-abort or by _broker.retire_channel — so every access to the old mount fails with ENOTCONN. The metadata store and cache directories are local to this pod and intact, so the same volume can be served again from a fresh channel with nothing lost that had reached them: writeback resumes uploading what it had staged.

Steps: stop whatever is left of the old adopter and drop its bookkeeping; retire its channel lease (the main premount stays dead for the pod’s lifetime, so a later mount leases a runtime channel); lease a fresh channel; start the client against the SAME meta and cache dirs; repoint the requested-path symlink; restart the report. Returns the new mount path. Only the broker path is supported — a privileged in-pod mount would need fusermount on a dead superblock.

Raises VolumeMountError if this instance has no live mount to recover, or the metadata dir is gone.