Configuration

Create a BabelQueue runtime and point it at your broker with a URL. The transport is chosen from the URL scheme — no separate “broker” flag.

Broker URL

from babelqueue import BabelQueue

# Redis (extra: babelqueue[redis])
app = BabelQueue("redis://localhost:6379/0", queue="orders")

# RabbitMQ (extra: babelqueue[amqp])
# app = BabelQueue("amqp://guest:guest@localhost:5672/", queue="orders")

# Amazon SQS (extra: babelqueue[sqs])
# app = BabelQueue("sqs://eu-central-1", queue="orders")

# Azure Service Bus (extra: babelqueue[azureservicebus])
# app = BabelQueue("sb://<namespace>.servicebus.windows.net", queue="orders")

# Apache Pulsar (extra: babelqueue[pulsar])
# app = BabelQueue("pulsar://localhost:6650", queue="orders")

# In-process, great for tests/local — no broker required
# app = BabelQueue("memory://", queue="orders")

Scheme	Transport	Requires
`memory://`	In-process (tests / local)	built in
`redis://`	Redis (reliable-queue pattern)	`babelqueue[redis]`
`amqp://`	RabbitMQ (via `pika`)	`babelqueue[amqp]`
`sqs://`	Amazon SQS (via `boto3`)	`babelqueue[sqs]`
`sb://`	Azure Service Bus (via `azure-servicebus`)	`babelqueue[azureservicebus]`
`pulsar://`	Apache Pulsar (via `pulsar-client`)	`babelqueue[pulsar]`

The sqs:// URL is sqs://<region> with optional query params: endpoint (LocalStack/ElasticMQ), prefix (a queue-URL prefix that skips GetQueueUrl), fifo=1, group_id, wait_time. The transport sends the canonical envelope with the §3 MessageAttributes and reconciles attempts to ApproximateReceiveCount − 1.

The sb:// URL is sb://<namespace>.servicebus.windows.net and authenticates with DefaultAzureCredential (Azure AD); pass connection_string=... to AsbTransport for SAS auth, or BabelQueue(transport=...) with a built client. It maps the envelope onto native Service Bus fields (§4) and reconciles attempts to max(body, DeliveryCount − 1).

The pulsar:// URL is pulsar://<host>:<port> (or pulsar+ssl://); pass a built client via BabelQueue(transport=...) for TLS/token auth. It projects the envelope onto native Pulsar message properties (bq-job = URN, plus the bq- fields, §5), defaults to a Shared subscription named babelqueue, and reconciles attempts to max(body, redelivery_count) — the redelivery count is 0-based, so no −1.

Options

Option	Default	Description
`queue`	`default`	Queue name written to `meta.queue`
`max_attempts`	—	Retries before a message is exhausted (bumps `attempts`)
`dead_letter`	`False`	Quarantine exhausted messages on `<queue>.dlq`
`on_unknown_urn`	`fail`	`fail` \| `delete` \| `release` \| `dead_letter`

app = BabelQueue(
    "redis://localhost:6379/0",
    queue="orders",
    max_attempts=3,
    dead_letter=True,
    on_unknown_urn="dead_letter",
)

Need just the wire codec, with no broker wiring? Import EnvelopeCodec directly — see Producing messages.

Next: Producing messages.