# Unreliable Async Processing

## The Problem You Recognize

You added async processing to handle background work — sending emails, processing payments, syncing data. But now you have new problems:

* Failed jobs **disappear silently** or retry forever with no visibility
* You **can't replay** a failed message after fixing the bug — the data is gone
* A **duplicate webhook** triggers the same handler twice, leading to double charges or duplicate emails
* Going async **required touching every handler** — adding queue configuration, serialization, and retry logic to each one
* **Retrying a failed event triggers all handlers again** — if one of three event handlers fails, the retry re-executes the two that already succeeded, causing side effects like duplicate emails or double charges

In **Laravel**, you've scattered `dispatch()` calls and `ShouldQueue` implementations across your codebase. In **Symfony**, you've configured Messenger transports and retry strategies in YAML, but each handler still needs custom error handling.

## What the Industry Calls It

**Resilient Messaging** — a combination of patterns: failure isolation (per-handler message delivery), automatic retries, error channels, dead letter queues, the outbox pattern for guaranteed delivery, and idempotency for deduplication.

## How Ecotone Solves It

With Ecotone, making a handler async is a single attribute. Resilience is built into the messaging layer — not bolted on per handler:

```php
// Make any handler async with one attribute
#[Asynchronous("notifications")]
#[EventHandler]
public function sendWelcomeEmail(UserRegistered $event): void
{
    // If this fails, Ecotone retries automatically
    // If it keeps failing, it goes to the dead letter queue
    // You can replay it after fixing the bug
}
```

**Failure isolation** — when multiple handlers subscribe to the same event, Ecotone delivers a separate copy of the message to each handler. If one fails, only that handler is retried — the others are not affected:

```php
#[Asynchronous("notifications")]
#[EventHandler]
public function sendWelcomeEmail(UserRegistered $event): void
{
    // If this fails, only this handler retries
    // The inventory handler below is NOT re-triggered
}

#[Asynchronous("inventory")]
#[EventHandler]
public function reserveInventory(UserRegistered $event): void
{
    // Runs independently — isolated from email handler failures
}
```

Retries, error channels, and dead letter queues are configured once at the channel level — every handler on that channel gets production resilience automatically. No per-handler boilerplate.

## Next Steps

* [Asynchronous Handling](/modelling/asynchronous-handling.md) — Make handlers async with a single attribute
* [Message Handling Isolation](/modelling/recovering-tracing-and-monitoring/message-handling-isolation.md) — Each handler gets its own message copy for safe retries
* [Retries](/modelling/recovering-tracing-and-monitoring/resiliency/retries.md) — Configure automatic retry strategies
* [Error Channel and Dead Letter](/modelling/recovering-tracing-and-monitoring/resiliency/error-channel-and-dead-letter.md) — Store failed messages for replay
* [Outbox Pattern](/modelling/recovering-tracing-and-monitoring/resiliency/outbox-pattern.md) — Guarantee message delivery
* [Idempotency (Deduplication)](/modelling/recovering-tracing-and-monitoring/resiliency/idempotent-consumer-deduplication.md) — Prevent double-processing

{% hint style="success" %}
**As You Scale:** Ecotone Enterprise adds [Command Bus Instant Retries](/modelling/recovering-tracing-and-monitoring/resiliency/retries.md#customized-instant-retries) for synchronous commands, [Command Bus Error Channel](/modelling/recovering-tracing-and-monitoring/resiliency/error-channel-and-dead-letter.md#command-bus-error-channel) for centralized error routing, and [Gateway-Level Deduplication](/modelling/recovering-tracing-and-monitoring/resiliency/idempotent-consumer-deduplication.md#deduplication-with-command-bus) that protects every handler behind a bus automatically.
{% endhint %}


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