Integration / RabbitMQ Interview Questions
Explain the execution flow of a publisher confirm?
Publisher confirms let a producer track, asynchronously, whether each message it published was actually accepted by the broker.
sequenceDiagram
participant P as Producer
participant B as Broker
P->>B: channel.confirm_select()
P->>B: basic.publish (delivery tag 1)
P->>B: basic.publish (delivery tag 2)
B-->>B: route + persist message 1
B-->>P: basic.ack (delivery tag 1)
B-->>B: message 2 could not be routed
B-->>P: basic.nack (delivery tag 2)
P->>P: mark tag 1 confirmed, retry/handle tag 2
The producer typically keeps a map of outstanding delivery tags to messages; on basic.ack it removes the tag as confirmed, and on basic.nack it can log, alert, or retry the failed message. RabbitMQ can also send a single ack covering a range of tags via the multiple flag, which is why batching acks improves throughput.
What must the producer call first to enable publisher confirms on a channel?
What does a basic.nack from the broker to the producer indicate?
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