What does auto.offset.reset=earliest vs latest do?

auto.offset.reset applies when Kafka has no initial offset for the consumer group (for example a new group) or when the current offset no longer exists on the server (for example because it was deleted). earliest resets to the earliest offset still available in the partition; latest resets to the latest offset, the end of the partition, so only records produced afterwards are read. none throws an exception if no previous offset exists for the group, and by_duration:<ISO 8601 duration> resets to a point in the past. The default is latest. If the group already has a valid committed offset, the setting is not used. With latest, adding partitions can cause message loss, because producers may write to a new partition before the consumers have offsets for it. A common practice is to pick earliest when existing records must be processed and latest when only new ones matter.

Expected key concepts: auto.offset.reset, earliest, latest, none, no initial offset, new group, committed offset, no longer exists, by_duration, exception