Getting Started

Here is a complete durable workflow in Zart. Every step persists its result — if your process dies and restarts, completed steps are skipped and the workflow continues from where it stopped.

use zart::{zart_durable, zart_step};
use zart::prelude::*;

// 1. Define steps as plain async functions
#[zart_step("send-email", retry = "exponential(3, 2s)")]
async fn send_email(email: &str) -> Result<(), StepError> {
    mailer.send(email, "Welcome!").await
}

#[zart_step("setup-billing")]
async fn setup_billing(email: &str) -> Result<CustomerId, StepError> {
    stripe.create_customer(email).await
}

// 2. Compose steps inside a durable handler — just call and await
#[zart_durable("onboarding")]
async fn onboarding(data: OnboardingData) -> Result<(), TaskError> {
    send_email(&data.email).await?;       // ✓ persisted, retried on failure
    setup_billing(&data.email).await?;    // ✓ persisted
    Ok(())
}

No context objects to thread through your code. Steps look and feel like plain async functions — they just happen to be durable.

Prerequisites

Rust 1.75 or later
A PostgreSQL 14+ database
A tokio runtime

Step 1: Add Dependencies

[dependencies]
zart          = "0.2"   # includes zart-macros — #[zart_durable] and #[zart_step] are ready to use
async-trait   = "0.1"
tokio         = { version = "1", features = ["full"] }
serde         = { version = "1", features = ["derive"] }
serde_json    = "1"
sqlx          = { version = "0.8", features = ["runtime-tokio", "postgres"] }

Step 2: Run Migrations

use sqlx::PgPool;
use zart::PgBackend;

let pool = PgPool::connect(&std::env::var("DATABASE_URL")?).await?;
let pg = PgBackend::new(pool);
pg.run_migrations().await?;

This creates the zart_tasks, zart_executions, zart_execution_runs, zart_steps, zart_step_attempts, and zart_pause_rules tables. Migrations are idempotent — safe to run on every deploy.

You can also run them from the CLI:

just migrate

Step 3: Register Handlers and Start a Worker

use zart::prelude::*;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let pool = PgPool::connect(&std::env::var("DATABASE_URL")?).await?;
    let pg = zart::PgBackend::new(pool);
    pg.run_migrations().await?;

    let config = zart::WorkerConfig {
        poll_interval: Duration::from_millis(200),
        max_tasks_per_poll: 10,
        max_concurrent_tasks: 4,
        shutdown_timeout: Duration::from_secs(5),
        orphan_timeout: Duration::from_secs(30),
        ..Default::default()
    };

    let worker = Arc::new(
        zart::WorkerBuilder::from_backend(&pg)
            .register_durable_task("onboarding", Onboarding)
            .config(config)
            .build(),
    );
    let w = worker.clone();
    tokio::spawn(async move { w.run().await });

    Ok(())
}

The worker polls PostgreSQL for due tasks and dispatches them to registered handlers. Multiple worker instances can run against the same database — SKIP LOCKED ensures each task is processed by exactly one worker.

Step 4: Schedule an Execution

Call this from anywhere — a web handler, a background task, a test:

let durable = DurableScheduler::from_backend(&pg);

durable
    .start_for::<Onboarding>(
        "signup-user-42",   // idempotency key — safe to call twice
        "onboarding",
        &OnboardingData { email: "alice@example.com".into() },
    )
    .await?;

Step 5: Wait for Completion (Optional)

The simplest approach is wait_completion, which blocks until the execution completes and automatically deserializes the result to your output type:

let output: MyOutput = durable
    .wait_completion("signup-user-42", Duration::from_secs(60), None)
    .await?;

println!("Workflow completed with output: {:?}", output);

No manual serde_json::from_value needed — the type parameter tells Zart exactly what to expect.

You can also combine start and wait into a single call:

let output = durable
    .start_and_wait_for::<Onboarding>("signup-user-42", "onboarding", &input, Duration::from_secs(60))
    .await?;

Run the Examples

The repository ships with runnable examples:

# Start PostgreSQL
docker compose up -d

# Run migrations
just migrate

# Try the sleep example
just example-sleep

# Try the brewery finder
just example-brewery

See the full Examples section for detailed walkthroughs.

Next Steps

Durable Execution — the core concept, lifecycle, and idempotency
Steps — defining steps, retries, sleeps, events, and durable values
Flow Control — parallel steps and durable loops
Error Handling — the three-way outcome model