Rust SDK

Use this guide for the general-access SDK surface, then continue to the generated API reference for individual types and methods. No Cloud account is required: the primary path uses the published Rust crate with a self-hosted Server. Developers already enrolled in Durable Workflow Cloud controlled early access can instead choose the clearly separate managed-runtime quickstart.

The first-party Rust SDK is a workflow-authoring surface, not only a protocol compatibility client. Rust authors deterministic workflows, activities, and long-running worker services against the same durable execution model used by PHP and Python. The async control-plane client starts, signals, queries, updates, cancels, terminates, and awaits executions; the worker runtime replays workflow history, runs workflow/activity/update handlers, reports worker and activity heartbeats, and exchanges language-neutral payloads with a self-hosted Server or Durable Workflow Cloud namespace runtime.

The Rust documentation landing page provides the SDK index and general entry points. For crate modules, structs, traits, and methods, continue to the generated Rust SDK API reference.

The stable Rust SDK supports durable timers, child workflows, activity retries and timeouts, local activities, worker sessions, sticky execution, signals, replayed query handlers, cancellation and termination, server-enforced workflow deadlines, typed side effects, version markers, updates, and typed terminal/replay failures. It does not yet claim schedule management. Use the 2.0 Capability Index instead of assuming every SDK has identical feature breadth.

Try the local Sample App playground

For the shortest no-Cloud authoring journey, open the current Sample App main branch in GitHub Codespaces and run:

scripts/playground rust

The local playground generates caller-owned workflow and activity source, selects the current stable artifacts, and starts the published Server and Waterline. It waits for a worker registration whose identity, workflow type, activity type, and task queue match the generated contract before starting the workflow. Success requires the expected completed result and history; the terminal then prints the exact local Waterline run link and the path to structured JSON evidence.

This intentionally small, transport-first scaffold uses serde_json::Value; it is not the only recommended Rust application contract. Continue to the crate's existing typed input/output example, retry, timeout, heartbeat, and terminal-failure activity policy example and local activity example. The package, repository example, and generated API reference below remain the direct paths for users who do not want Sample App.

Package and source

• Crate on crates.io
• Source repository

Install the Rust SDK from the last passing qualified tuple. The exact requirement is generated from the same machine-readable authority as the Server quickstart:

cargo add durable-workflow@=3.4.1

Or declare the same qualified requirement directly in Cargo.toml:

[dependencies]
durable-workflow = "=3.4.1"

The crate requires Rust 1.86 or newer. Its package metadata declares the exact qualified Durable Workflow Server range, worker protocol 1.19, and control plane 2. During deployment, the protocol manifests advertised by GET /api/cluster/info remain authoritative.

Server negotiates worker-protocol headers within major 1: a server advertising 1.N accepts a worker header 1.M only when M <= N. Rust SDK ordinary workers send X-Durable-Workflow-Protocol-Version: 1.19 and require a server advertising 1.19 or newer. The qualified Server advertises 1.20. The opt-in cooperative cancellation profile requires 1.20.

Negotiation fails closed. A missing or malformed header, a different major, or a worker minor newer than the server's advertised minor is rejected. The server version range selects the release family; it does not override the runtime protocol manifest.

Local activities

Rust SDK 3.1.0 adds inline local execution on workers configured with Worker::local_activities(true). Register callbacks with the ordinary activity registration methods, then use the workflow context's local activity methods. See the runnable example and LocalActivityOptions reference for retry and timeout configuration.

Server records the terminal result for cold replay. Uncommitted local effects can execute again after worker loss and must be idempotent. Async callbacks must yield to Tokio. Blocking work needs separate process supervision. Inline local execution and prepared cooperative local supervision use separate worker profiles.

Worker sessions

Enable Worker::worker_sessions(true) and declare the requirements your worker satisfies with capabilities(...). Route remote activities with in_worker_session(WorkerSessionOptions::new(session_id)). The activity context provides the shared handle through worker_session(). Explicit handles support create(), renew() and close(reason) after worker registration.

Bound worker session count with max_concurrent_worker_sessions(...) and session activity concurrency with max_concurrent_activities(...). Renew idle handles explicitly. Activity heartbeats also renew the holder lease, preserving the original absolute TTL. An async callback that yields to Tokio is dropped when its locally observed lease or TTL expires without requiring application heartbeats.

Session resources live in the holder process. A replacement must rebuild them, and interrupted external effects need idempotency and attempt fencing. Committed results replay without rerunning the callback. Graceful shutdown closes held sessions before deregistration. Local activities cannot use session routing.

Session support starts with Rust SDK 3.2.0. Use Server 2.5.1 or newer. The runnable example reuses a process-local cache across two typed activities and prints its generation. See WorkerSessionOptions and WorkerSession for configuration and lifecycle methods.

Bounded sticky execution

Enable Worker::sticky_cache(StickyCacheOptions::new(capacity)) to retain immutable encoded history for subsequent replay. The cache is disabled by default. Set max_history_bytes(...) and ttl(...) to bound retained history and its lifetime. Allow additional memory for decoding and replay.

The cache uses workflow, run and build identity. Worker replacement, expiry, eviction or an invalid history cursor falls back to complete durable history. Terminal workflows and stopped workers discard their entries. Workflow code must replay correctly with an empty cache.

Support starts with Rust SDK 3.4.0 and the qualified Server baseline. See the configuration reference, runnable example and portable worker-affinity guide.

Prepare the released repository example

The repository's hello_world example registers a Rust worker, starts a workflow, sends a signal, runs an activity, reports an activity heartbeat, and waits for the completed result. Because that example runs the application client and worker in one process, the no-account path below connects it to a self-hosted Server. A provisioned Cloud namespace is an optional secondary runtime with separate role-scoped credentials.

For a reproducible source exercise, obtain the exact crate source recorded by the qualified tuple. The value below is generated from that machine-readable authority. The example directory is absolute so either connection path can enter it directly:

export DURABLE_WORKFLOW_RUST_VERSION=3.4.1
export DURABLE_WORKFLOW_RUST_EXAMPLE_DIR="$PWD/durable-workflow-rust-${DURABLE_WORKFLOW_RUST_VERSION}"
git clone --depth 1 --single-branch --branch "$DURABLE_WORKFLOW_RUST_VERSION" \
  https://github.com/durable-workflow/sdk-rust.git "$DURABLE_WORKFLOW_RUST_EXAMPLE_DIR"

Run the combined example with self-hosted Server

The unmodified hello_world example accepts one token for a self-hosted Durable Workflow Server whose authentication policy allows the same credential to make workflow commands and poll for work:

cd "$DURABLE_WORKFLOW_RUST_EXAMPLE_DIR"
DURABLE_WORKFLOW_SERVER_URL=http://localhost:8080 \
DURABLE_WORKFLOW_TOKEN=dev-token \
cargo run --example hello_world

The example uses the default namespace provisioned by the local Server quickstart. Use TASK_QUEUE to override its default rust-workers task queue. No Cloud enrollment or Cloud credential is involved in this path.

Optional secondary path: connect to Durable Workflow Cloud

For the shortest managed-runtime proof, use the Rust Cloud quickstart. It runs the same symmetric Sample App playground available to PHP and Python, selects current stable artifacts dynamically, verifies exact worker readiness, and waits for a completed result.

Servicio gestionado · grupo limitado

Grupo de lanzamiento de Durable Workflow Cloud

Already enrolled in Cloud? Run the shared Rust playground against your provisioned namespace with separate role-scoped runtime credentials.

Solicita acceso anticipado

The lower-level combined SDK example below is useful when adapting an existing Rust process. Export the values returned when Cloud provisions the namespace and creates its two runtime credentials:

See Cloud Managed Runtime for the managed connection boundary.

export DURABLE_WORKFLOW_RUNTIME_URL='https://your-runtime-url'
export DURABLE_WORKFLOW_RUNTIME_NAMESPACE='orders'
export DURABLE_WORKFLOW_CLIENT_TOKEN='dwr_client_credential'
export DURABLE_WORKFLOW_WORKER_TOKEN='dwr_worker_credential'

In $DURABLE_WORKFLOW_RUST_EXAMPLE_DIR/examples/hello_world.rs, replace the existing server_url, token, and Client::builder(...) setup with this split-token builder configuration:

let runtime_url = std::env::var("DURABLE_WORKFLOW_RUNTIME_URL")
    .expect("DURABLE_WORKFLOW_RUNTIME_URL must be set");
let runtime_namespace = std::env::var("DURABLE_WORKFLOW_RUNTIME_NAMESPACE")
    .expect("DURABLE_WORKFLOW_RUNTIME_NAMESPACE must be set");
let client_token = std::env::var("DURABLE_WORKFLOW_CLIENT_TOKEN")
    .expect("DURABLE_WORKFLOW_CLIENT_TOKEN must be set");
let worker_token = std::env::var("DURABLE_WORKFLOW_WORKER_TOKEN")
    .expect("DURABLE_WORKFLOW_WORKER_TOKEN must be set");

let client = Client::builder(runtime_url)
    .namespace(runtime_namespace)
    .control_token(Some(client_token))
    .worker_token(Some(worker_token))
    .build()?;

Then run the example normally:

cd "$DURABLE_WORKFLOW_RUST_EXAMPLE_DIR"
cargo run --example hello_world

The example's workflow start, signal, describe, and result calls use control_token; its Worker registration, polling, heartbeat, and completion calls use worker_token. Both roles use the same Cloud-provided runtime URL, runtime namespace, and task queue, but they do not reuse a credential. Do not replace either Cloud credential with .token(...): that method is the generic single-token fallback used by the self-hosted configuration above.

Start with server-enforced workflow timeouts

The Rust SDK provides WorkflowStartOptions and Client::start_workflow_with_options for workflow deadlines that the server enforces even after the starting process exits. Execution timeout covers the whole workflow instance, including continue-as-new runs; run timeout covers one run and is recomputed when a new run begins.

use durable_workflow::{json, Client, Result, WorkflowStartOptions};

async fn start(client: &Client) -> Result<()> {
    let handle = client.start_workflow_with_options(
        "orders.await-payment",
        "orders",
        "order-42",
        WorkflowStartOptions::new()
            .execution_timeout_seconds(300)
            .run_timeout_seconds(30),
        json!([{"order_id": "order-42"}]),
    ).await?;

    println!("workflow={} run={:?}", handle.workflow_id, handle.run_id);
    Ok(())
}

Both values are seconds, must be positive, and the run timeout cannot exceed the execution timeout. The existing Client::start_workflow convenience method uses WorkflowStartOptions::default(): a 3600-second execution timeout and a 600-second run timeout. See Timeouts for the server's deadline and continue-as-new semantics.

These are workflow policy, not HTTP or result-polling timeouts. In particular, WorkflowResultOptions::timeout only stops the local result() call from waiting. It does not close, cancel, or otherwise change the workflow run. The caller can inspect the returned identity and wait again. An execution or run deadline configured with WorkflowStartOptions is durable server state; when it expires, the server closes the run with a terminal timed_out outcome.

Deterministic parallel groups

WorkflowContext::parallel and its join alias compose activities, child workflows, timers, mixed groups, and nested groups without adding a new Server command. Constructors on ParallelOperation defer every leaf until the entire tree is known:

use durable_workflow::{json, ChildWorkflowOptions, ParallelOperation};
use std::time::Duration;

let results = ctx.parallel(vec![
    ParallelOperation::activity("load-profile", json!(["customer-42"])),
    ParallelOperation::group(vec![
        ParallelOperation::child_workflow(
            "quote-shipping",
            ChildWorkflowOptions::new("shipping-workers"),
            json!(["customer-42"]),
        ),
        ParallelOperation::timer(Duration::from_secs(1)),
    ]),
]).await?;

Every leaf carries the shared stable group identity plus its complete outer-to-inner path. Successful results retain nested input shape and order. Error::ParallelFailed preserves the typed leaf cause, deterministic member path, group path, and completed siblings. Pending and completed histories replay without rescheduling; exact duplicates and late completions do not change the chosen positional outcome.

Durable first-completion selection

WorkflowContext::select and select_keyed start activities, child workflows, timers, signals, condition waits, and nested ordinary groups together, then resume from the winner recorded by the runtime:

use durable_workflow::{json, ParallelOperation, SelectionKey};
use std::time::Duration;

let selected = ctx.select_keyed(vec![
    ("resolver", ParallelOperation::activity("resolve-request", json!([request_id]))),
    ("input", ParallelOperation::signal("resolution.received")),
    ("deadline", ParallelOperation::timer(Duration::from_secs(2))),
]).await?;

if selected.key == SelectionKey::Name("deadline".to_string()) {
    if let Some(resolver) = selected.handle(&SelectionKey::Name("resolver".to_string())) {
        resolver.cancel().await?;
    }
}

SelectionResult preserves the stable key/index, operation kind and identity, typed value or failure, and a DurableOperationHandle for every member. A loser continues unless workflow code later awaits handle.await_result() or awaits handle.cancel(). The cancellation future resolves to unit; only committed SelectionOperationCancelled history proves cancellation won. Replay advances past an unmarked request, and await_result() still returns a completion that committed first. Restart and replay consume the persisted winner; later or duplicate terminal events cannot change it.

Saga compensation

Register a compensation only after the corresponding forward activity has completed, then give the forward result to Saga::finish:

let mut saga = ctx.saga();
let outcome = async {
    let flight = ctx.activity("trip.reserve-flight", json!([])).await?;
    saga.add_compensation("trip.cancel-flight", json!([flight]))?;

    let hotel = ctx.activity("trip.reserve-hotel", json!([])).await?;
    saga.add_compensation("trip.cancel-hotel", json!([hotel]))?;

    ctx.activity("trip.charge", json!([])).await?;
    Ok(json!({"status": "booked"}))
}.await;

saga.finish(outcome).await

Handled failure runs the existing activity command in reverse registration order, one compensation at a time. Compensation stops at its first failure. Error::SagaCompensationFailed preserves both typed errors, the compensation activity type, and its registration order through restart and replay. Terminal cancel_workflow does not resume workflow code to run compensations.

Deterministic side effects and version markers

The Rust SDK records small non-deterministic values with WorkflowContext::side_effect and derives deterministic UUIDv4 values with WorkflowContext::uuid_v4. A cold replay decodes the recorded value instead of invoking the callback again; reordered, missing, duplicate, or codec-incompatible markers return a typed Error::NonDeterministicReplay.

Use WorkflowContext::get_version(change_id, min_supported, max_supported) to keep old and new workflow branches replay-compatible during a rollout. New runs record max_supported; existing runs reuse the durable marker. patched(change_id) provides the boolean rollout form, and deprecate_patch(change_id) preserves the marker after the legacy branch has drained. See Side Effects and Versioning for the shared durable semantics.

Cancel, terminate, and handle terminal outcomes

Service-mode cancel_workflow and terminate_workflow both close the run immediately. They record distinct terminal outcomes, but neither asks workflow code to run cleanup. Use request_cancellation() with cooperating workers for bounded workflow cleanup. See the cooperative cancellation guide for operation policies, supervision and recovery.

use durable_workflow::{Client, WorkflowCommandOptions};

# async fn cancel(client: &Client) -> durable_workflow::Result<()> {
client.cancel_workflow(
    "order-42",
    WorkflowCommandOptions::new()
        .reason("customer withdrew the order")
        .request_id("cancel-order-42"),
).await?;
# Ok(())
# }

Instance-targeted cancel_workflow and terminate_workflow resolve the current run on the server. For selected-run safety, call cancel_workflow_run or terminate_workflow_run, or use a handle's cancel_selected_run and terminate_selected_run methods. If a selected run is stale, Error::WorkflowCommandRejected exposes the stable historical_run_command_rejected reason together with workflow ID, run ID, target scope, HTTP status, and the response body.

Successful WorkflowHandle::result calls continue to return the decoded JSON value. Match the typed terminal variants for every other outcome. Branch on the stable reason and category fields instead of display text:

use durable_workflow::{Error, WorkflowHandle, WorkflowResultOptions};

# async fn wait(handle: WorkflowHandle) -> durable_workflow::Result<()> {
match handle.result(WorkflowResultOptions::default()).await {
    Ok(value) => println!("completed: {value}"),
    Err(Error::WorkflowCancelled(outcome)) => {
        println!("cancelled {:?}: {}", outcome.run_id, outcome.reason);
    }
    Err(Error::WorkflowTerminated(outcome)) => {
        println!("terminated: {}", outcome.reason);
    }
    Err(Error::WorkflowFailed(outcome)) => {
        println!("failure {:?}: {:?}", outcome.failure_id, outcome.exception_class);
    }
    Err(Error::WorkflowTimedOut(outcome)) => match (
        outcome.reason.as_str(),
        outcome.failure_category.as_deref(),
    ) {
        ("result_wait_timeout", Some("client_timeout")) => {
            println!(
                "caller deadline for {} / {:?}; the run may still be open",
                outcome.workflow_id, outcome.run_id,
            );
        }
        ("execution_timeout" | "run_timeout", category) => {
            println!(
                "server timeout for {} / {:?}: reason={} category={:?}",
                outcome.workflow_id, outcome.run_id, outcome.reason, category,
            );
        }
        (reason, category) => {
            println!("other typed timeout: reason={reason} category={category:?}");
        }
    }
    Err(error) => return Err(error),
}
# Ok(())
# }

Each terminal outcome carries workflow and run identity. It also retains the public reason, failure category and identity, exception type and class, non-retryable state, message, and exception payload when the server supplies them. A local wait deadline has reason result_wait_timeout and category client_timeout; a server timeout is a terminal timed_out run whose stable reason is execution_timeout or run_timeout.

Handles returned by either start method retain the selected run_id. WorkflowHandle::result describes that run-specific route, so reusing the same workflow ID for a newer run cannot make a wait silently report the newer run's outcome. Preserve both outcome.workflow_id and outcome.run_id in logs, metrics, and retry records; use instance-level lookups only when following the current run is intentional.

Workflow updates

Rust supports durable updates across application-client, selected-handle, and worker-authoring roles. Use Client::update_workflow or WorkflowHandle::update for JSON-compatible values, and the matching update_workflow_avro_value or update_avro_value methods for explicitly typed Avro values.

Workers register named handlers with Worker::register_update; use register_update_avro_value when the handler consumes and returns Avro values directly. An update is a durable, result-bearing workflow mutation. It is separate from fire-and-forget signals and read-only replayed queries.

Payload envelope

Workflow input, signals, activities, queries, and results use the published PayloadEnvelope contract: a codec plus encoded blob. The SDK's default avro path uses its declared apache-avro dependency and the platform's fixed versioned Value schema; do not hand-roll the blob or replace the envelope with an implementation-specific record.

use durable_workflow::{decode_payload, json, PayloadEnvelope, Result, Value};

fn round_trip() -> Result<()> {
    let envelope = PayloadEnvelope::avro(&json!({"order_id": "order-42"}))?;
    assert_eq!(envelope.codec, "avro");

    let decoded: Value = decode_payload(&envelope)?;
    assert_eq!(decoded["order_id"], "order-42");
    Ok(())
}

start_workflow and start_workflow_with_options apply this envelope automatically to their serializable input. Use the public helpers only when a program needs to exchange an envelope directly.

Long-running activities should heartbeat and inspect should_stop(). On cancellation, release temporary files, connections, or other process-local resources and return promptly. A late completion is rejected by durable state and cannot convert a cancelled or terminated run into success; managed workers continue polling after that definitive rejection and after restart.

For server images, authentication, and production topology, continue with the server setup guide.