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Baggage#

OpenTelemetry Baggage is a context propagation mechanism that allows you to pass custom metadata or key-value pairs across service boundaries, providing additional context for distributed tracing and observability.

FastStream Baggage#

FastStream provides a convenient abstraction over baggage that allows you to:

  • Initialize the baggage
  • Propagate baggage through headers
  • Modify the baggage
  • Stop propagating baggage

Example#

To initialize the baggage and start distributing it, follow this example:

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from faststream.opentelemetry import Baggage

headers = Baggage({"hello": "world"}).to_headers()
await broker.publish("hello", "first", headers=headers)

All interactions with baggage at the consumption level occurs through the CurrentBaggage object, which is automatically injected from the context:

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from faststream.opentelemetry import CurrentBaggage

@broker.subscriber("first")
@broker.publisher("second")
async def response_handler_first(msg: str, baggage: CurrentBaggage):
    print(baggage.get_all())  # {'hello': 'world'}
    baggage.remove("hello")
    baggage.set("user-id", 1)
    baggage.set("request-id", "UUID")
    print(baggage.get("user-id"))  # 1
    return msg


@broker.subscriber("second")
@broker.publisher("third")
async def response_handler_second(msg: str, baggage: CurrentBaggage):
    print(baggage.get_all())  # {'user-id': '1', 'request-id': 'UUID'}
    baggage.clear()
    return msg


@broker.subscriber("third")
async def response_handler_third(msg: str, baggage: CurrentBaggage):
    print(baggage.get_all())  # {}

Note

If you consume messages in batches, then the baggage from each message will be merged into the common baggage available through the get_all method. However, you can still retrieve a list of all the baggage from the batch using the get_all_batch method.