Event-driven architecture

Event-driven systems decouple services in time and space. That is exactly what makes them scalable and resilient, and exactly what makes them hard to reason about. “Exactly once” is rarely something the infrastructure can promise on its own. Ordering usually holds only within a partition. And an event schema, once published, is a public API for as long as anyone consumes it.

What we do

• Event modelling. Finding the facts the business actually cares about, naming them well, and designing events that stay meaningful as the system evolves.
• Delivery semantics you can state. At-least-once delivery combined with idempotent consumers, deduplication and the transactional outbox pattern, so that “effectively once” is a property of the design rather than a hope.
• Ordering and partitioning. Partition keys that preserve the ordering you need without creating hot spots.
• Event sourcing and CQRS, where an auditable, replayable history earns its keep, and honest advice when it doesn’t.
• Backpressure and flow control. Consumers that slow producers down gracefully instead of falling over, and dead-letter queues that someone actually watches.
• Schema evolution. Versioning strategies and compatibility checks in CI, so producers and consumers can be deployed independently.

Built in Rust

Rust’s async ecosystem lets us build consumers and stream processors that sustain high message rates with predictable memory use and no garbage-collection pauses. The type system keeps message handling exhaustive: add a new event variant and the compiler lists every place that has to handle it.

pub enum AccountEvent {
    Opened { id: AccountId, owner: OwnerId },
    Credited { id: AccountId, amount: Amount },
    Debited { id: AccountId, amount: Amount },
    Frozen { id: AccountId, reason: FreezeReason },
}

fn apply(state: &mut Account, event: &AccountEvent) -> Result<(), ApplyError> {
    match event {
        AccountEvent::Opened { .. } => state.open(),
        AccountEvent::Credited { amount, .. } => state.credit(*amount),
        AccountEvent::Debited { amount, .. } => state.debit(*amount),
        AccountEvent::Frozen { reason, .. } => state.freeze(*reason),
        // No catch-all arm: a new variant is a compile error until handled.
    }
}

Typical engagements

• Designing an event backbone for a growing set of services
• Migrating from synchronous request chains to asynchronous, event-driven flows
• Fixing duplicate, lost or out-of-order processing in an existing pipeline