Apache Zookeeper's poison packet

The leader election and failure detection mechanisms are fairly mature, and typically just work… until they don’t.
Four different bugs resulting in random cluster-wide lockups. Two of those bugs laid in ZooKeeper, and the other two were lurking in the Linux kernel. This is the story.
https://www.pagerduty.com/blog/the-discovery-of-apache-zookeepers-poison-packet/