Middleware Overview

Add cross-cutting concerns to your sagas.

Middleware Pipeline

Press enter or space to select a node.You can then use the arrow keys to move the node around. Press delete to remove it and escape to cancel.

Press enter or space to select an edge. You can then press delete to remove it or escape to cancel.

Available Middleware

Package	Purpose
Logging	Structured logging
Tracing	OpenTelemetry spans
Metrics	Prometheus metrics
Validation	Schema validation
Idempotency	Deduplication
Tenant	Multi-tenancy

Using Middleware

import { createBus } from '@saga-bus/core';
import { createLoggingMiddleware } from '@saga-bus/middleware-logging';
import { createTracingMiddleware } from '@saga-bus/middleware-tracing';
import { createMetricsMiddleware } from '@saga-bus/middleware-metrics';

const bus = createBus({
  transport,
  store,
  sagas: [{ definition: orderSaga }],
  middleware: [
    createLoggingMiddleware({ level: 'info' }),
    createTracingMiddleware({ serviceName: 'order-worker' }),
    createMetricsMiddleware({ prefix: 'saga_bus' }),
  ],
});

Middleware Order

Order matters! Recommended order:

1. Logging (first - logs everything)
2. Tracing (creates spans for downstream)
3. Metrics (records timing)
4. Validation (reject invalid early)
5. Idempotency (check duplicates)
6. Tenant (extract context)

Creating Custom Middleware

See Custom Middleware.