[KAFKA-14426] Add documentation for Kraft limtations that have open KIPs

• Type: Task
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: documentation, kraft
• Assignee: Unassigned
• Reporter: Greg Harris
• Created: 30/Nov/22 21:42
• Updated: 06/Jul/23 22:27

Description

Currently there are a number of limitations for Kraft, which are described as the motivation for the following open KIPs:

• https://cwiki.apache.org/confluence/display/KAFKA/KIP-853%3A+KRaft+Controller+Membership+Changes
• https://cwiki.apache.org/confluence/display/KAFKA/KIP-856%3A+KRaft+Disk+Failure+Recovery
• https://cwiki.apache.org/confluence/display/KAFKA/KIP-650%3A+Enhance+Kafkaesque+Raft+semantics#KIP650:EnhanceKafkaesqueRaftsemantics-Pre-vote 

These limitations are:

• No online method of resizing the controller quorum
• No online method of recovering from controller disk loss
• No support for heterogeneous voter lists in running controller nodes
• When using a quorum size 3, there is no live-upgrade roll which is tolerant of a single unplanned machine failure.
• When using a quorum size >3, there is a risk of zombie leaders causing extended outages without the pre-vote feature.

These are significant enough concerns for operations of a Kraft-enabled cluster that they should be documented as official limitations in the ops documentation.

Optionally, we may wish to provide or link to more detailed operations documentation about performing the offline-resize or offline-recovery stages, in addition to describing that such offline procedures are necessary.

Issue Links

• is related to: KAFKA-14207 Add a 6.10 section for KRaft
• relates to: KAFKA-14094 KIP-853: KRaft controller membership changes
• relates to: KAFKA-14113 KIP-856: KRaft Disk Failure Recovery