Boyang Chen created KAFKA-7995:
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Summary: Augment singleton protocol type to list for Kafka
Consumer
Key: KAFKA-7995
URL: https://issues.apache.org/jira/browse/KAFKA-7995
Project: Kafka
Issue Type: Improvement
Components: consumer, core
Reporter: Boyang Chen
Right now Kafka consumer protocol uses a singleton marker to distinguish Kafka
Connect worker and normal consumer. This is not upgrade-friendly approach since
the protocol type could potential change over time. A better approach is to
support multiple candidacies so that the no downtime protocol type switch could
achieve.
For example, if we are trying to upgrade a Kafka Streams application towards a
protocol type called "stream", right now there is no way to do this without
downtime since broker will reject changing protocol type to a different one
unless the group is back to empty. If we allow new member to provide a list of
protocol type instead ("consumer", "stream"), there would be no compatibility
issue.
Alternative approach is to invent an admin API to change group's protocol type
on runtime. However, the burden introduced on administrator is not trivial,
since we need to guarantee the operation series to be correct, otherwise we
will see limp-upgrade experience in the midpoint, for example while we are
changing protocol type there was unexpected rebalance that causes old members
join failure.
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