From 66c729da663e81c3302b67aa6c5fe296984792a7 Mon Sep 17 00:00:00 2001
From: Konstantin Osipov <kostja@scylladb.com>
Date: Sat, 27 Feb 2021 17:35:04 +0300
Subject: [PATCH] raft: set the current leader upon getting InstallSnapshot

If the current leader is set, the follower will not vote
for another candidate. This is also known as "sticky leadership" rule.

Before this change, the rule was enacted only upon receiving
AppendEntries RPC from the leader. Turn it on also upon receiving
InstallSnapshot RPC.
---
 raft/fsm.hh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/raft/fsm.hh b/raft/fsm.hh
index ba222dbcf3..191f2d9f74 100644
--- a/raft/fsm.hh
+++ b/raft/fsm.hh
@@ -386,7 +386,8 @@ void fsm::step(server_id from, Message&& msg) {
         logger.trace("{} [term: {}] received a message with higher term from {} [term: {}]",
             _my_id, _current_term, from, msg.current_term);
 
-        if constexpr (std::is_same_v<Message, append_request>) {
+        if constexpr (std::is_same_v<Message, append_request> ||
+                      std::is_same_v<Message, install_snapshot>) {
             leader = from;
         } else {
             if constexpr (std::is_same_v<Message, vote_request>) {