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https://issues.apache.org/jira/browse/KAFKA-8638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17111427#comment-17111427
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Hai Lin commented on KAFKA-8638:
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What's the current status is this kip? I see this will be very useful when we
do any operation on the cluster. Like during rolling restart, first blacklist
the broker and bounce it, until it got fully replicated, re enable it again.
Most of the time, when a broker come up after a restart, some small partition
will get synced faster than those big ones. And the broker is under a lot of
stressed when replicating for those big partitions, but small partition become
leader and the performance is compromised. I think even a simple blacklist
white-list would be very helpful.
> Preferred Leader Blacklist (deprioritized list)
> -----------------------------------------------
>
> Key: KAFKA-8638
> URL: https://issues.apache.org/jira/browse/KAFKA-8638
> Project: Kafka
> Issue Type: Improvement
> Components: config, controller, core
> Affects Versions: 1.1.1, 2.3.0, 2.2.1
> Reporter: GEORGE LI
> Assignee: GEORGE LI
> Priority: Major
>
> Currently, the kafka preferred leader election will pick the broker_id in the
> topic/partition replica assignments in a priority order when the broker is in
> ISR. The preferred leader is the broker id in the first position of replica.
> There are use-cases that, even the first broker in the replica assignment is
> in ISR, there is a need for it to be moved to the end of ordering (lowest
> priority) when deciding leadership during preferred leader election.
> Let’s use topic/partition replica (1,2,3) as an example. 1 is the preferred
> leader. When preferred leadership is run, it will pick 1 as the leader if
> it's ISR, if 1 is not online and in ISR, then pick 2, if 2 is not in ISR,
> then pick 3 as the leader. There are use cases that, even 1 is in ISR, we
> would like it to be moved to the end of ordering (lowest priority) when
> deciding leadership during preferred leader election. Below is a list of use
> cases:
> * (If broker_id 1 is a swapped failed host and brought up with last segments
> or latest offset without historical data (There is another effort on this),
> it's better for it to not serve leadership till it's caught-up.
> * The cross-data center cluster has AWS instances which have less computing
> power than the on-prem bare metal machines. We could put the AWS broker_ids
> in Preferred Leader Blacklist, so on-prem brokers can be elected leaders,
> without changing the reassignments ordering of the replicas.
> * If the broker_id 1 is constantly losing leadership after some time:
> "Flapping". we would want to exclude 1 to be a leader unless all other
> brokers of this topic/partition are offline. The “Flapping” effect was seen
> in the past when 2 or more brokers were bad, when they lost leadership
> constantly/quickly, the sets of partition replicas they belong to will see
> leadership constantly changing. The ultimate solution is to swap these bad
> hosts. But for quick mitigation, we can also put the bad hosts in the
> Preferred Leader Blacklist to move the priority of its being elected as
> leaders to the lowest.
> * If the controller is busy serving an extra load of metadata requests and
> other tasks. we would like to put the controller's leaders to other brokers
> to lower its CPU load. currently bouncing to lose leadership would not work
> for Controller, because after the bounce, the controller fails over to
> another broker.
> * Avoid bouncing broker in order to lose its leadership: it would be good if
> we have a way to specify which broker should be excluded from serving
> traffic/leadership (without changing the replica assignment ordering by
> reassignments, even though that's quick), and run preferred leader election.
> A bouncing broker will cause temporary URP, and sometimes other issues. Also
> a bouncing of broker (e.g. broker_id 1) can temporarily lose all its
> leadership, but if another broker (e.g. broker_id 2) fails or gets bounced,
> some of its leaderships will likely failover to broker_id 1 on a replica with
> 3 brokers. If broker_id 1 is in the blacklist, then in such a scenario even
> broker_id 2 offline, the 3rd broker can take leadership.
> The current work-around of the above is to change the topic/partition's
> replica reassignments to move the broker_id 1 from the first position to the
> last position and run preferred leader election. e.g. (1, 2, 3) => (2, 3, 1).
> This changes the replica reassignments, and we need to keep track of the
> original one and restore if things change (e.g. controller fails over to
> another broker, the swapped empty broker caught up). That’s a rather tedious
> task.
> KIP is located at
> [KIP-491|https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=120736982]
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