Oleksiy, Where are you specifying the version? Unless I'm missing something, the JoinGroup protocol doesn't include versions so I'm not sure I understand the examples you are giving. Are the version numbers included in the per-protocol metadata?
You can see exactly how the consumer coordinator on the broker selects the protocol here: https://github.com/apache/kafka/blob/trunk/core/src/main/scala/kafka/coordinator/GroupMetadata.scala#L179 It is just taking the candidate protocols (ones that are available for all consumers), then has each consumer "vote" by selecting whichever candidate appears in its list of strategies first, then uses the one with the most votes. Is it possible your example is behaving the way it is because it actually has duplicates for "strategyX", and in the last case it chooses the first strategyX despite the conflicting versions? -Ewen On Wed, Dec 23, 2015 at 9:44 AM, Oleksiy Krivoshey <oleks...@gmail.com> wrote: > Hi, > > I can't understand how the protocol upgrades (to newer version) should > work. When I send GroupJoinRequest with a list of assignment protocols > (same protocol name, different versions) always the first protocol/version > gets picked up as a member version. Even if all consumers in the group are > configured with two versions still always the first specified version will > be selected by coordinator and not the one with highest version number. > > So for example: > consumer1: [ {name:strategyX, version: 0}, {name: strategyX, version: 1} ] > consumer2: [ {name:strategyX, version: 0}, {name: strategyX, version: 1} ] > > Both will be assigned a version 0 in a response to leader. If I make it > this way: > > consumer1: [ {name:strategyX, version: 1}, {name: strategyX, version: 0} ] > consumer2: [ {name:strategyX, version: 1}, {name: strategyX, version: 0} ] > > Both will be assigned version 1. > > In this case: > > consumer1: [ {name:strategyX, version: 10}, {name: strategyX, version: 1} ] > consumer2: [ {name:strategyX, version: 20}, {name: strategyX, version: 1} ] > > Kafka will endlessly try to rebalance the group without success because > consumer1 will have version:10 and consumer2 - version:20 in a > GroupJoinResponse. > > Can anyone please explain the process of the protocol version upgrade? > -- Thanks, Ewen
