Add raft_voter_contact()

[ralight]

This returns the number of voting nodes that are recently in contact with the leader, to allow determining if the cluster is currently in a degraded / at risk state.

I'd be interested on your thoughts on this. At the moment it feels like not being able to find out this information is an omission.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d67cffd) 77.13% compared to head (2e103cb) 77.10%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #492      +/-   ##
==========================================
- Coverage   77.13%   77.10%   -0.03%     
==========================================
  Files          52       52              
  Lines        9839     9847       +8     
  Branches     2514     2516       +2     
==========================================
+ Hits         7589     7593       +4     
- Misses       1068     1072       +4     
  Partials     1182     1182              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[cole-miller]

Not speaking for the rest of the team, but this seems reasonable to me. I would like a note in the docstring that the return value is not to be relied on for correctness (since it could be out of date), and a couple of tests.

[ralight]

@cole-miller Thanks for the feedback. I've added the initialisation to 0 on init, reset to 1 on changing to a leader, and added a test which starts off with 3 nodes, kills off a node, and revives the node, with checks at each step. If you'd like more tests please give me some hints on the direction to go in.

[MathieuBordere]

Thanks for this, seems useful.

[cole-miller]

Thanks!