Distributed database seems like a quite complex project. Let's say I could do a minimal version of etcd using raft or paxos over the weekend but it would probably take most of my weekend's time, I think 10-20 hours work at least. That is not reasonable as a home work for job interview.
Something which takes 2-3 hours is much more reasonable and I am willing to do that because it leaves me with enough time for family / life over the weekend or to do homework for few different companies to not put all my eggs into single basket when interviewing.
If you are looking for a job you would rarely only concentrate on one opportunity. For sure you would try to compare at least 2-3 comparable jobs to choose the one which fits you best. So these sort of tests / home work assignments should be quite simple, probably algorithmic questions which can be completed in 50-100 lines of code.
Raft or Paxos are used for partition tolerance and there are implementations that you can use. Maybe you will spend more time but you will learn something useful.
You will easily spend 10-20h for "normal" coding interview.
5h to refresh basic algorithms BFS, DFS, sorts, Trees.
2h for hackerrank challenge from clueless HR person
3h for another preparation before whiteboarding on site
1h whiteboarding before any design question is asked
A benefit of "normal" interview process is that you chase multiple opportunities and your prep time will compound for better results.
I think it depends on the applicant, I'm willing to do such a project but the prices I will demand if hired will be markedly higher than a firm that offered me a simpler project that consumed less time. The way I see it is you have limited the risk you have undertaken in hiring me thus I can see more of the fruits of my labor.
Something which takes 2-3 hours is much more reasonable and I am willing to do that because it leaves me with enough time for family / life over the weekend or to do homework for few different companies to not put all my eggs into single basket when interviewing.
If you are looking for a job you would rarely only concentrate on one opportunity. For sure you would try to compare at least 2-3 comparable jobs to choose the one which fits you best. So these sort of tests / home work assignments should be quite simple, probably algorithmic questions which can be completed in 50-100 lines of code.