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a9063f9582
Whenever a Raft configuration change is performed, `raft::server` calls `raft_rpc::add_server`/`raft_rpc::remove_server`. Our `raft_rpc` implementation has a function, `_on_server_update`, passed in the constructor, which it called in `add_server`/`remove_server`; that function would update the set of endpoints detected by the direct failure detector. `_on_server_update` was passed an IP address and that address was added to / removed from the failure detector set (there's another translation layer between the IP addresses and internal failure detector 'endpoint ID's; but we can ignore it for the purposes of this commit). Therefore: the failure detector was pinging a certain set of IP addresses. These IP addresses were updated during Raft configuration changes. To implement the `is_alive(raft::server_id)` function (required by `raft::failure_detector` interface), we would translate the ID using the Raft address map, which is currently also updated during configuration changes, to an IP address, and check if that IP address is alive according to the direct failure detector (which maintained an `_alive_set` of type `unordered_set<gms::inet_address>`). This all works well but it assumes that servers can be identified using IP addresses - it doesn't play well with the fact that servers may change their IP addresses. The only immutable identifier we have for a server is `raft::server_id`. In the future, Raft configurations will not associate IP addresses with Raft servers; instead we will assume that IP addresses can change at any time, and there will be a different mechanism that eventually updates the Raft address map with the latest IP address for each `raft::server_id`. To prepare us for that future, in this commit we no longer operate in terms of IP addresses in the failure detector, but in terms of `raft::server_id`s. Most of the commit is boilerplate, changing `gms::inet_address` to `raft::server_id` and function/variable names. The interesting changes are: - in `is_alive`, we no longer need to translate the `raft::server_id` to an IP address, because now the stored `_alive_set` already contains `raft::server_id`s instead of `gms::inet_address`es. - the `ping` function now takes a `raft::server_id` instead of `gms::inet_address`. To send the ping message, we need to translate this to IP address; we do it by the `raft_address_map` pointer introduced in an earlier commit. Thus, there is still a point where we have to translate between `raft::server_id` and `gms::inet_address`; but observe we now do it at the last possible moment - just before sending the message. If we have no translation, we consider the `ping` to have failed - it's equivalent to a network failure where no route to a given address was found. Closes #11759 * github.com:scylladb/scylladb: direct_failure_detector: get rid of complex `endpoint_id` translations service/raft: ping `raft::server_id`s, not `gms::inet_address`es service/raft: store `raft_address_map` reference in `direct_fd_pinger` gms: gossiper: move `direct_fd_pinger` out to a separate service gms: gossiper: direct_fd_pinger: extract generation number caching to a separate class