fix: handle missing previous_cluster in pre_append_log_follower#600
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kjnilsson merged 6 commits intorabbitmq:mainfrom Mar 26, 2026
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@Qian-Cheng-nju thank you for contributing to RabbitMQ. Please add a license header to the new test module and sign our CLA when you have a moment. |
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Thanks! @michaelklishin License header added. I've sent an email to sign the CLA. |
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Hi all! I have signed the CLA! Please feel free to contact me if you need anything else. |
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@Qian-Cheng-nju I think the fix looks fine but I would like the test for it to be added to one of the existing test suites, not a new suite of it's own. |
kjnilsson
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Please add the test to one of the existing test suites
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Thanks @kjnilsson! Moved the test into ra_server_SUITE as follower_cluster_change_overwrite. |
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Hi, thanks for ra!
I found a crash scenario in pre_append_log_follower and put together a fix.
When a follower receives an uncommitted cluster change entry at index I, then a new leader overwrites that index with a regular entry, pre_append_log_follower crashes with {badkey, previous_cluster}. This happens because the follower path doesn't store previous_cluster in the state map when processing cluster changes, but the overwrite path assumes it's always there.
The trigger scenario: follower gets AER with cluster change at index 4 (term 5), then gets AER from a new leader overwriting index 4 with a regular entry (term 6). The second AER crashes the follower process.