[KUDU-2455] Don't crash when flushing cmeta with empty config

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.7.0
• Component/s: consensus
• Assignee: Unassigned
• Reporter: Mike Percy
• Created: 24/May/18 22:10
• Updated: 24/May/18 22:10

Description

We saw a case in the wild where there was a missing cmeta file due to a crash in the middle of a tablet copy, resulting in the replica starting up in a tombstoned state. When the replica attempted to vote while tombstoned, it crashed when syncing its vote to disk with the message "RaftConfig must have at least one peer" from VerifyRaftConfig().

I think we can support this scenario. In order to do that, we should remove that check from that location, put it somewhere else (perhaps in ChangeConfig()), and add a test for this scenario.