Author here - yes, Failsafe-go definitely took some inspiration from Polly, but it also borrows ideas from the Failsafe JVM library [1]. Polly and Failsafe influenced each other back and forth over the years.
Author here - I do get this critique, and of course API design is subjective, but there was a rationale behind the design choices. Putting each policy in its own package allowed the API to be slightly more concise. And having the API use a generic to represent a function's result type allowed different parts of the API to be independent and composable while still ensuring that result types align. A bit more on that here:
This, usually. It's fair to point out that very specialized clocks, such as Google uses with Spanner, can allow you to achieve some consistency without coordination/locks, but for pretty much anyone else the rule you stated very much applies.
I'm not sure that merely checking the result of some set of operations - whether a mutex is held by the expected process - tells you very much about the validity of how that mutex was obtained (assuming interleaving requests and such). This is where you need to explore the history, which is what the linearizability checker does and which is what Jepsen tests generally use.
It is a bit of work and learning curve writing a Jepsen test suite, but it's not too bad, particularly with the excellent docs that Kyle has recently written:
Leader election generally[1] requires consensus among distributed processes, and global locks generally[1] require consensus as well. The benefit of this is that both problems can be solved on top of a common consensus implementation which is what http://atomix.io does.
1: I say generally because you can do fancy things with fancy clocks to avoid running operations through a quorum under certain circumstances, but these carry caveats that preclude them from being reliable enough to use in many use cases.
The article calls on someone(?) to Jepsen test Redlock, which is a good idea, but I think that the author(s) of such systems should release their own Jepsen test suite along with the software they're purporting to be safe (as others have done [1][2][3]). I would suspect that operations on Redlock, when subjected to nemesis that partition, kill and skew-clocks on various nodes, would not be found linearizable.
In general, I don't understand why one would build a system that attempts to approximate consensus without just using one of the proven consensus algorithms. Redlock is not the only one here, there are other systems that do this as well.