The following scenario is possible: a node A changes its IP
from ip1 to ip2 with restart, other nodes are not yet aware of ip2
so they keep gossiping ip1, after restart A receives
ip1 in a gossip message and calls handle_major_state_change
since it considers it as a new node. Then on_join event is
called on the gossiper notification handles, we receive
such event in raft_ip_address_updater and reverts the IP
of the node A back to ip1.
The essence of the problem is that we don't pass the proper
generation when we add ip2 as a local IP during initialization
when node A restarts, so the zero generation is used
in raft_address_map::add_or_update_entry and the gossiper
message owerwrites ip2 to ip1.
In this commit we fix this problem by passing the new generation.
To do that we move the increment_and_get_generation call
from join_token_ring to scylla_main, so that we have a new generation
value before init_address_map is called.
Also we remove the load_initial_raft_address_map function from
raft_group0 since it's redundant. The comment above its call site
says that it's needed to not miss gossiper updates, but
the function storage_service::init_address_map where raft_address_map
is now initialized is called before gossiper is started. This
function does both - it load the previously persisted host_id<->IP
mappings from system.local and subscribes to gossiper notifications,
so there is no room for races.
Note that this problem reproduces less likely with the
'raft topology: ip change: purge old IP' commit - other
nodes remove the old IP before it's send back to the
just restarted node. This is also the reason why this
problem doesn't occur in gossiper mode.
fixesscylladb/scylladb#17199
4b33ba2894