Initial host of the cluster may change

[karol-kokoszka]

Scylla Manager keep 'host' as a property of cluster in the database. This host is coordinator node that is considered to be used as a first node when SM creates the scylla client to interact with Scylla API. If the host value is not correct, then the only possibility of updating this value is by calling sctool cluster update --host <new_host>.

It can be improved, by letting SM to override the host value with one of the existing nodes when the SM realizes that the host doesn't exist anymore.

[karol-kokoszka]

refirement notes

To mitigate the problem which appears when the "coordinator node" is removed, we can:

• on 'validateHostsConnectivity`, to include known hosts to discover others (valid for cluster update operation)
• create more informative error on host validation during the cluster update to warn user that this "coordinator host" is unreachable and the cluster should be updated with the new --host value if the coordinator doesn't exist anymore