AMQP (RabbitMQ)

AMQP via RabbitMQ is the production default for distributed deployments. Mature, widely deployed, with excellent tooling.

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Why AMQP

Strength	Benefit
Mature	15+ years of production use
Durable queues	Messages survive broker restarts
Flexible routing	Topic exchanges, headers, fanout
Management UI	Built-in web console
Dead letter queues	Automatic failure handling

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Configuration

[bus]
backend = "amqp"

[bus.amqp]
url = "amqp://guest:guest@localhost:5672"
exchange = "angzarr.events"
prefetch_count = 10

Environment Variables

export AMQP_URL="amqp://guest:guest@localhost:5672"
export BUS_BACKEND="amqp"

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Exchange Topology

Angzarr creates a topic exchange for event routing:

flowchart LR
    EX["Exchange: angzarr.events<br/>(topic)"]
    EX -->|"player.#"| PP[queue: player-projector]
    EX -->|"player.#"| OP[queue: output-projector]
    EX -->|"hand.#"| HS[queue: hand-saga]

Routing Keys

Events are published with routing keys: {domain}.{event_type}

player.PlayerRegistered
player.FundsDeposited
hand.CardsDealt
hand.HandComplete

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Queue Configuration

Each handler gets a dedicated queue with configurable durability:

# Handler queue settings
queues:
  player-projector:
    durable: true
    auto_delete: false
    exclusive: false
    arguments:
      x-dead-letter-exchange: angzarr.dlx

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Dead Letter Handling

Failed messages route to a dead letter exchange:

flowchart LR
    DLX["angzarr.dlx<br/>(fanout)"] --> DLQ["angzarr.dlq<br/>(queue)"]

Monitor the DLQ for processing failures:

# Check DLQ depth
rabbitmqctl list_queues name messages | grep dlq

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Helm Deployment

values.yaml

bus:
  backend: amqp

amqp:
  enabled: true
  host: rabbitmq.messaging.svc.cluster.local
  port: 5672
  credentials:
    secretName: rabbitmq-credentials
    usernameKey: username
    passwordKey: password

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Testing

# Run AMQP tests (requires testcontainers)
cargo test --test bus_amqp --features amqp

# Requires podman socket
systemctl --user start podman.socket

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Management Console

RabbitMQ includes a web management interface:

http://localhost:15672
Default credentials: guest/guest

Monitor:

• Queue depths
• Message rates
• Consumer connections
• Exchange bindings

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When to Use AMQP

• Production default — Most deployments
• Existing RabbitMQ — Already in infrastructure
• Complex routing — Headers, topics, fanout
• Operational maturity — Team familiarity

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Next Steps

• Kafka — High-throughput alternative
• Testcontainers — Container-based testing