Dead letters

max_attempts(n) caps deliveries per record; dead_letter(stream) names the stream a spent record leaves for, and a cap without one retires the record.

The cap counts the first delivery too. Kinesis keeps no delivery count, so the count travels with the record in RETRY_COUNT_HEADER. Under a cap every retry is a copy published back to the stream, the immediate retry too, because only a copy carries the count forward. When a retry would make the delivery the n-th one, the runtime settles it and publishes the record to the dead-letter stream instead, without the delay. The record keeps its payload, its headers and its partition key; its retry count says how many times it was delivered. A cap without a dead-letter stream checkpoints past the spent record, as drop does. The dead-letter stream is an ordinary stream of the service's own infrastructure: a subscription of the same service, or of another one, reads it.

Example

An order gets four deliveries; the fourth one that still cannot be settled goes to orders.unsettled.

Macros

examples/kinesis_retry.rs

fn service(broker: KinesisBroker) -> RustStream {
    RustStream::new(AppInfo::new("orders", "0.1.0")).with_broker(broker, |b| {
        // Four deliveries per order, then the record leaves for a stream an operator reads.
        b.include(reconcile)
            .max_attempts(nonzero!(4))
            .dead_letter("orders.unsettled");
    })
}

Manual

examples/manual/kinesis_retry.rs

fn service(broker: KinesisBroker) -> RustStream {
    RustStream::new(AppInfo::new("orders", "0.1.0")).with_broker(broker, |b| {
        // Four deliveries per order, then the record leaves for a stream an operator reads.
        b.include(subscriber(KinesisStream::new("orders"), Reconcile).build())
            .max_attempts(nonzero!(4))
            .dead_letter("orders.unsettled");
    })
}