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Clarify documentation for :on_success and :on_failure #73

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Sep 24, 2020
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Clarify documentation for :on_success and :on_failure #73

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16 changes: 11 additions & 5 deletions lib/broadway_rabbitmq/producer.ex
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Expand Up @@ -177,16 +177,22 @@ defmodule BroadwayRabbitMQ.Producer do
* `:ack` - acknowledge the message. RabbitMQ will mark the message as acked and
will not redeliver it to any other consumer.

* `:reject` - rejects the message without requeuing (basically, discards the message).
RabbitMQ will not redeliver the message to any other consumer.
* `:reject` - rejects the message without requeuing (basically, discards
the message). RabbitMQ will not redeliver the message to any other
consumer, but a queue can be configured to send rejected messages to a
[dead letter exchange](https://www.rabbitmq.com/dlx.html), where another
consumer can see why it was dead lettered, how many times, etc, and
potentially republish it.

* `:reject_and_requeue` - rejects the message and tells RabbitMQ to requeue it so
that it can be delivered to a consumer again. `:reject_and_requeue` always
requeues the message.
that it can be delivered to a consumer again. `:reject_and_requeue`
always requeues the message. If the message is unprocessable, this will
cause an infinite loop of retries.
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@nathanl nathanl Sep 24, 2020 •
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The infinite loop of retries bit us in production, which is why I think this clarification is important.

I would like to suggest that, rather than defaulting to :reject_and_requeue, the user be required to specify one of these options. This would prompt them to consider the tradeoffs.


* `:reject_and_requeue_once` - rejects the message and tells RabbitMQ to requeue it
the first time. If a message was already requeued and redelivered, it will be
rejected and not requeued again.
rejected and not requeued again. This feature uses Broadway-specific message metadata,
not RabbitMQ's dead lettering feature.

## Metadata

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