Expose previous GRANDPA round's missed votes in grandpa_roundState RPC

[wpank]

Right now the current behavior when calling thegrandpa_roundState RPC call is dumping the internal state of GRANDPA, which can include the previous round, background, if it is still in progress.

A useful addition to this endpoint would be to include the previous round's missed votes, regardless of whether the previous round has terminated not, as this will give a strong alert-able condition for a validator if their node is not working correctly. This is also useful for alerting from nodes that are not connected to the validating infrastructure.

[dillu24]

Since the rounds change frequently, would there be any way of accessing historical rounds? Because previous round data would be lost immediately.

[dillu24]

Has there been any movement with regards to this issue? For PANIC we would like to query historical rounds to try and detect whether validators are participating in GRANDPA consensus.

[andresilva]

We added this to the roadmap so it's planned to be tackled but most likely will only happen next year. In the meantime Darwinia has developed a tool for monitoring which maybe suits your use case: https://github.com/darwinia-network/grandma