resonate-external-system-of-record-pattern-rust

Resonate External System of Record Pattern — Rust

SDK note (0.6.0). ctx.get_dependency::<T>() and resonate.with_dependency::<T>(value) are real pub fns in the Rust SDK source (resonate-sdk-rs:resonate/src/context.rs, resonate.rs) but are not yet covered in docs/develop/rust.mdx. The APIs are safe to use; cite source paths when reviewers ask.

Overview

When a Rust workflow touches an external system with its own durability (a database, a ledger, a message broker), that system often is or should be the system of record (SoR). Resonate coordinates the workflow and guarantees at-least-once execution; the SoR enforces consistency via its own primitives (transactions, idempotency keys, CAS operations).

Rust's type-dispatched dependency injection makes this pattern particularly clean: register typed resources once at process start with resonate.with_dependency<T>(value), retrieve inside durable functions with ctx.get_dependency::<T>().

For the language-agnostic framing, see resonate-external-system-of-record-pattern-typescript. Rust's shape adds: Arc<T> returns from DI, serde-derived input types, and idiomatic sqlx / ledger-crate usage.

Core principle

Write to the system of record first. Read from it as ground truth. Never let Resonate's promise state contradict the SoR.

Resonate stores workflow state (what step succeeded, what the result was). The SoR stores business state (the account balance, the order status). When they disagree, the SoR wins; Resonate's job is to converge toward it.

Dependency setup (ephemeral world)

use resonate::prelude::*;
use sqlx::PgPool;
use std::sync::Arc;

#[tokio::main]
async fn main() -> Result<()> {
    let pool = PgPool::connect(&std::env::var("DATABASE_URL")?).await?;
    let stripe = stripe::Client::new(std::env::var("STRIPE_SECRET_KEY")?);

    let resonate = Resonate::new(ResonateConfig::default())
        .with_dependency(pool)
        .with_dependency(stripe);

    resonate.register(create_order).unwrap();
    resonate.register(charge_card).unwrap();

    tokio::signal::ctrl_c().await?;
    resonate.stop().await?;
    Ok(())
}