Cassandra has a neat feature that lets you expire data in a column. Using this handy little feature, you can create simple leadership election using cassandra. The whole process is described here which talks about leveraging Cassandras consensus and the column expiration to create leadership electors.
The idea is that a user will try and claim a slot for a period of time in a leadership table. If a slot is full, someone else has leadership. While the leader is still active they needs to heartbeat the table faster than the columns TTL to act as a keepalive. If it fails to heartbeat (i.e. it died) then its leadership claim can be relinquished and someone else can claim it. Unlike most leadership algorithms that claim a single “host” as a leader, I needed a way to create leaders sharded by some “group”. I call this a “LeadershipGroup” and we can … Read more