Vector was designed with a focus on providing clear guarantees. Below you'll find a support matrix so you know exactly what type of guarantee you can expect for your combination of sources and sinks. This helps you make the appropriate tradeoffs or your usecase.
"At least once" delivery guarantees that an event received by Vector will be delivered at least once to the configured destination(s). While rare, it is possible for an event to be delivered more than once (see the Does Vector support exactly once delivery FAQ below).
To achieve at least once delivery your source must be configured to use
disk based buffers:
[sinks.my_sink_id]# ...[sinks.my_sink_id.buffer]type = "disk"when_full = "block"max_size = 104900000 # 100MiB
Each sink documents the buffer options.
"Best effort" delivery has no guarantees and means that Vector will make a best effort to deliver each event. This means it is possible for the occasional event to not be lost.
One of the unique advantages of the logging use case is that data is usually used for diagnostic purposes only. Therefore, losing the occasional event has little impact on your business. This affords you the opportunity to provision your pipeline towards performance, simplicity, and cost reduction. On the other hand, if you're using your data to perform business critical functions, then data loss is not acceptable and therefore requires "at least once" delivery.
To clarify, even though a source or sink is marked as "best effort" it does not mean Vector takes delivery lightly. In fact, once data is within the boundary of Vector it will not be lost if you've configured on-disk buffers. Data loss for "best effort" sources and sinks are almost always due to the limitations of the underlying protocol.
No, Vector does not support exactly once delivery. There are future plans to partially support this for sources and sinks that support it (Kafka, for example), but it remains unclear if Vector will ever be able to achieve this. We recommend subscribing to our mailing list, which will keep you in the loop if this ever changes.