> For the complete documentation index, see [llms.txt](https://hanfak.gitbook.io/workspace/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hanfak.gitbook.io/workspace/integration/delivery.md).

# Delivery

* Delivery of messages/requests in distributed systems
* we can’t deliver messages reliably and in order in the face of network partitions and crashes without a high degree of coordination. This coordination, of course, comes at a cost (latency and availability), while still relying on at-least-once semantics.

## at-most-once delivery

## at-least-once delivery

* at-least-once delivery is also impossible because, technically speaking, network partitions are not strictly time-bound.
  * If the connection from you to the server is interrupted indefinitely, you can’t deliver anything.

## Exactly once delivery

* impossible
  * See the two generals problem
* <https://bravenewgeek.com/you-cannot-have-exactly-once-delivery/>