From 26ce9264a0393086dc0008559b2da4e8d7675ebd Mon Sep 17 00:00:00 2001
From: Erik Grinaker <grinaker@cockroachlabs.com>
Date: Tue, 20 Jun 2023 10:45:36 +0000
Subject: [PATCH 1/3] rafttest: add `log-level` argument for `stabilize`

Signed-off-by: Erik Grinaker <grinaker@cockroachlabs.com>
---
 rafttest/interaction_env_handler.go           | 15 ++---
 rafttest/interaction_env_handler_stabilize.go | 17 +++++-
 rafttest/interaction_env_logger.go            | 34 +++++++++++
 .../async_storage_writes_append_aba_race.txt  |  2 +-
 testdata/campaign_learner_must_vote.txt       |  6 +-
 testdata/checkquorum.txt                      |  2 +-
 testdata/confchange_v1_remove_leader.txt      |  2 +-
 testdata/confchange_v2_replace_leader.txt     |  2 +-
 .../heartbeat_resp_recovers_from_probing.txt  |  2 +-
 testdata/prevote.txt                          |  2 +-
 testdata/prevote_checkquorum.txt              |  2 +-
 testdata/probe_and_replicate.txt              | 58 +++++++++----------
 testdata/replicate_pause.txt                  | 10 ++--
 testdata/slow_follower_after_compaction.txt   |  8 +--
 testdata/snapshot_succeed_via_app_resp.txt    |  6 +-
 15 files changed, 107 insertions(+), 61 deletions(-)

diff --git a/rafttest/interaction_env_handler.go b/rafttest/interaction_env_handler.go
index d78adbb7..3c1ddbfa 100644
--- a/rafttest/interaction_env_handler.go
+++ b/rafttest/interaction_env_handler.go
@@ -182,20 +182,17 @@ func (env *InteractionEnv) Handle(t *testing.T, d datadriven.TestData) string {
 	default:
 		err = fmt.Errorf("unknown command")
 	}
-	if err != nil {
-		env.Output.WriteString(err.Error())
-	}
 	// NB: the highest log level suppresses all output, including that of the
 	// handlers. This comes in useful during setup which can be chatty.
 	// However, errors are always logged.
-	if env.Output.Len() == 0 {
-		return "ok"
-	}
-	if env.Output.Lvl == len(lvlNames)-1 {
-		if err != nil {
+	if err != nil {
+		if env.Output.Quiet() {
 			return err.Error()
 		}
-		return "ok (quiet)"
+		env.Output.WriteString(err.Error())
+	}
+	if env.Output.Len() == 0 {
+		return "ok"
 	}
 	return env.Output.String()
 }
diff --git a/rafttest/interaction_env_handler_stabilize.go b/rafttest/interaction_env_handler_stabilize.go
index d79a9aa4..084022ab 100644
--- a/rafttest/interaction_env_handler_stabilize.go
+++ b/rafttest/interaction_env_handler_stabilize.go
@@ -25,7 +25,22 @@ import (
 )
 
 func (env *InteractionEnv) handleStabilize(t *testing.T, d datadriven.TestData) error {
-	idxs := nodeIdxs(t, d)
+	idxs := nodeIdxs(t, d) // skips key=value args
+	for _, arg := range d.CmdArgs {
+		for i := range arg.Vals {
+			switch arg.Key {
+			case "log-level":
+				defer func(old int) {
+					env.Output.Lvl = old
+				}(env.Output.Lvl)
+				var level string
+				arg.Scan(t, i, &level)
+				if err := env.LogLevel(level); err != nil {
+					return err
+				}
+			}
+		}
+	}
 	return env.Stabilize(idxs...)
 }
 
diff --git a/rafttest/interaction_env_logger.go b/rafttest/interaction_env_logger.go
index 78298f54..0fcf94d6 100644
--- a/rafttest/interaction_env_logger.go
+++ b/rafttest/interaction_env_logger.go
@@ -102,3 +102,37 @@ func (l *RedirectLogger) Panicf(format string, v ...interface{}) {
 	// and testing the cases when panic is expected.
 	panic(fmt.Sprintf(format, v...))
 }
+
+// Override StringBuilder write methods to silence them under NONE.
+
+func (l *RedirectLogger) Quiet() bool {
+	return l.Lvl == len(lvlNames)-1
+}
+
+func (l *RedirectLogger) Write(p []byte) (int, error) {
+	if l.Quiet() {
+		return 0, nil
+	}
+	return l.Builder.Write(p)
+}
+
+func (l *RedirectLogger) WriteByte(c byte) error {
+	if l.Quiet() {
+		return nil
+	}
+	return l.Builder.WriteByte(c)
+}
+
+func (l *RedirectLogger) WriteRune(r rune) (int, error) {
+	if l.Quiet() {
+		return 0, nil
+	}
+	return l.Builder.WriteRune(r)
+}
+
+func (l *RedirectLogger) WriteString(s string) (int, error) {
+	if l.Quiet() {
+		return 0, nil
+	}
+	return l.Builder.WriteString(s)
+}
diff --git a/testdata/async_storage_writes_append_aba_race.txt b/testdata/async_storage_writes_append_aba_race.txt
index b1e82f12..4b68330f 100644
--- a/testdata/async_storage_writes_append_aba_race.txt
+++ b/testdata/async_storage_writes_append_aba_race.txt
@@ -18,7 +18,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level info
 ----
diff --git a/testdata/campaign_learner_must_vote.txt b/testdata/campaign_learner_must_vote.txt
index 14530b55..85617df3 100644
--- a/testdata/campaign_learner_must_vote.txt
+++ b/testdata/campaign_learner_must_vote.txt
@@ -25,7 +25,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 # Propose a conf change on n1 that promotes n3 to voter.
 propose-conf-change 1
@@ -36,13 +36,13 @@ ok
 # Commit and fully apply said conf change. n1 and n2 now consider n3 a voter.
 stabilize 1 2
 ----
-ok (quiet)
+ok
 
 # Drop all inflight messages to 3. We don't want it to be caught up when it is
 # asked to vote.
 deliver-msgs drop=(3)
 ----
-ok (quiet)
+ok
 
 # We now pretend that n1 is dead, and n2 is trying to become leader.
 
diff --git a/testdata/checkquorum.txt b/testdata/checkquorum.txt
index ed69a529..b25c1e63 100644
--- a/testdata/checkquorum.txt
+++ b/testdata/checkquorum.txt
@@ -18,7 +18,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
diff --git a/testdata/confchange_v1_remove_leader.txt b/testdata/confchange_v1_remove_leader.txt
index 68aab846..8c4c7f91 100644
--- a/testdata/confchange_v1_remove_leader.txt
+++ b/testdata/confchange_v1_remove_leader.txt
@@ -15,7 +15,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
diff --git a/testdata/confchange_v2_replace_leader.txt b/testdata/confchange_v2_replace_leader.txt
index 8074188d..6bfe9fe5 100644
--- a/testdata/confchange_v2_replace_leader.txt
+++ b/testdata/confchange_v2_replace_leader.txt
@@ -21,7 +21,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level info
 ----
diff --git a/testdata/heartbeat_resp_recovers_from_probing.txt b/testdata/heartbeat_resp_recovers_from_probing.txt
index 690f563a..e606a155 100644
--- a/testdata/heartbeat_resp_recovers_from_probing.txt
+++ b/testdata/heartbeat_resp_recovers_from_probing.txt
@@ -20,7 +20,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
diff --git a/testdata/prevote.txt b/testdata/prevote.txt
index d65103ed..db763d35 100644
--- a/testdata/prevote.txt
+++ b/testdata/prevote.txt
@@ -19,7 +19,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
diff --git a/testdata/prevote_checkquorum.txt b/testdata/prevote_checkquorum.txt
index 939d6f36..6db6662b 100644
--- a/testdata/prevote_checkquorum.txt
+++ b/testdata/prevote_checkquorum.txt
@@ -17,7 +17,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
diff --git a/testdata/probe_and_replicate.txt b/testdata/probe_and_replicate.txt
index 8e61b618..d5829704 100644
--- a/testdata/probe_and_replicate.txt
+++ b/testdata/probe_and_replicate.txt
@@ -44,7 +44,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 propose 1 prop_1_12
 ----
@@ -56,7 +56,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 ## Create term 2 entries.
 campaign 2
@@ -65,15 +65,15 @@ ok
 
 stabilize 2
 ----
-ok (quiet)
+ok
 
 stabilize 6
 ----
-ok (quiet)
+ok
 
 stabilize 2 5 7
 ----
-ok (quiet)
+ok
 
 propose 2 prop_2_15
 ----
@@ -85,11 +85,11 @@ ok
 
 stabilize 2 7
 ----
-ok (quiet)
+ok
 
 deliver-msgs drop=(1,2,3,4,5,6,7)
 ----
-ok (quiet)
+ok
 
 ## Create term 3 entries.
 campaign 7
@@ -98,15 +98,15 @@ ok
 
 stabilize 7
 ----
-ok (quiet)
+ok
 
 stabilize 1 2 3 4 5 6
 ----
-ok (quiet)
+ok
 
 stabilize 7
 ----
-ok (quiet)
+ok
 
 propose 7 prop_3_18
 ----
@@ -126,11 +126,11 @@ ok
 
 stabilize 7
 ----
-ok (quiet)
+ok
 
 deliver-msgs drop=(1,2,3,4,5,6,7)
 ----
-ok (quiet)
+ok
 
 ## Create term 4 entries.
 campaign 6
@@ -139,7 +139,7 @@ ok
 
 stabilize 1 2 3 4 5 6
 ----
-ok (quiet)
+ok
 
 propose 6 prop_4_15
 ----
@@ -147,7 +147,7 @@ ok
 
 stabilize 1 2 4 5 6
 ----
-ok (quiet)
+ok
 
 propose 6 prop_4_16
 ----
@@ -159,11 +159,11 @@ ok
 
 stabilize 6
 ----
-ok (quiet)
+ok
 
 deliver-msgs drop=(1,2,3,4,5,6,7)
 ----
-ok (quiet)
+ok
 
 ## Create term 5 entries.
 campaign 5
@@ -172,7 +172,7 @@ ok
 
 stabilize 1 2 4 5
 ----
-ok (quiet)
+ok
 
 propose 5 prop_5_17
 ----
@@ -180,11 +180,11 @@ ok
 
 stabilize 1 2 4 5
 ----
-ok (quiet)
+ok
 
 deliver-msgs drop=(1,2,3,4,5,6,7)
 ----
-ok (quiet)
+ok
 
 ## Create term 6 entries.
 campaign 4
@@ -193,7 +193,7 @@ ok
 
 stabilize 1 2 4 5
 ----
-ok (quiet)
+ok
 
 propose 4 prop_6_19
 ----
@@ -201,7 +201,7 @@ ok
 
 stabilize 1 2 4
 ----
-ok (quiet)
+ok
 
 propose 4 prop_6_20
 ----
@@ -209,7 +209,7 @@ ok
 
 stabilize 1 4
 ----
-ok (quiet)
+ok
 
 propose 4 prop_6_21
 ----
@@ -217,11 +217,11 @@ ok
 
 stabilize 4
 ----
-ok (quiet)
+ok
 
 deliver-msgs drop=(1,2,3,4,5,6,7)
 ----
-ok (quiet)
+ok
 
 ## Create term 7 entries.
 campaign 5
@@ -230,15 +230,15 @@ ok
 
 stabilize 5
 ----
-ok (quiet)
+ok
 
 stabilize 1 3 6 7
 ----
-ok (quiet)
+ok
 
 stabilize 5
 ----
-ok (quiet)
+ok
 
 propose 5 prop_7_20
 ----
@@ -254,11 +254,11 @@ ok
 
 stabilize 5
 ----
-ok (quiet)
+ok
 
 deliver-msgs drop=(1,2,3,4,5,6,7)
 ----
-ok (quiet)
+ok
 
 
 # Show the Raft log from each node.
diff --git a/testdata/replicate_pause.txt b/testdata/replicate_pause.txt
index 67e64a95..d9cee59f 100644
--- a/testdata/replicate_pause.txt
+++ b/testdata/replicate_pause.txt
@@ -18,7 +18,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 # Propose 3 entries.
 propose 1 prop_1_12
@@ -36,7 +36,7 @@ ok
 # Store entries and send proposals.
 process-ready 1
 ----
-ok (quiet)
+ok
 
 # Re-enable log messages.
 log-level debug
@@ -57,7 +57,7 @@ ok
 # Commit entries between nodes 1 and 2.
 stabilize 1 2
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
@@ -105,7 +105,7 @@ ok
 # Commit entries between nodes 1 and 2 again.
 stabilize 1 2
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
@@ -176,7 +176,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
diff --git a/testdata/slow_follower_after_compaction.txt b/testdata/slow_follower_after_compaction.txt
index 0b169b78..0d3d48c8 100644
--- a/testdata/slow_follower_after_compaction.txt
+++ b/testdata/slow_follower_after_compaction.txt
@@ -16,7 +16,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 # Propose 3 entries.
 propose 1 prop_1_12
@@ -33,7 +33,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 # Re-enable log messages.
 log-level debug
@@ -70,7 +70,7 @@ ok
 # Commit entries on nodes 1 and 2.
 stabilize 1 2
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
@@ -107,7 +107,7 @@ ok
 
 stabilize
 ----
-ok (quiet)
+ok
 
 log-level debug
 ----
diff --git a/testdata/snapshot_succeed_via_app_resp.txt b/testdata/snapshot_succeed_via_app_resp.txt
index a52a683e..80ed3646 100644
--- a/testdata/snapshot_succeed_via_app_resp.txt
+++ b/testdata/snapshot_succeed_via_app_resp.txt
@@ -23,16 +23,16 @@ ok
 # Fully replicate everything, including the leader's empty index.
 stabilize
 ----
-ok (quiet)
+ok
 
 compact 1 11
 ----
-ok (quiet)
+ok
 
 # Drop inflight messages to n3.
 deliver-msgs drop=(3)
 ----
-ok (quiet)
+ok
 
 # Show the Raft log messages from now on.
 log-level debug

From 09ea4c5573e3b0d5a50d31164f510467244389c8 Mon Sep 17 00:00:00 2001
From: Erik Grinaker <grinaker@cockroachlabs.com>
Date: Fri, 16 Jun 2023 17:29:23 +0000
Subject: [PATCH 2/3] rafttest: show term and leader for `raft-state`

Signed-off-by: Erik Grinaker <grinaker@cockroachlabs.com>
---
 rafttest/interaction_env_handler_raftstate.go |  3 +-
 testdata/confchange_v1_remove_leader.txt      | 24 +++++++--------
 testdata/confchange_v2_replace_leader.txt     | 30 +++++++++----------
 3 files changed, 29 insertions(+), 28 deletions(-)

diff --git a/rafttest/interaction_env_handler_raftstate.go b/rafttest/interaction_env_handler_raftstate.go
index 3117b2f7..e40a192b 100644
--- a/rafttest/interaction_env_handler_raftstate.go
+++ b/rafttest/interaction_env_handler_raftstate.go
@@ -42,7 +42,8 @@ func (env *InteractionEnv) handleRaftState() error {
 		} else {
 			voterStatus = "(Non-Voter)"
 		}
-		fmt.Fprintf(env.Output, "%d: %s %s\n", st.ID, st.RaftState, voterStatus)
+		fmt.Fprintf(env.Output, "%d: %s %s Term:%d Lead:%d\n",
+			st.ID, st.RaftState, voterStatus, st.Term, st.Lead)
 	}
 	return nil
 }
diff --git a/testdata/confchange_v1_remove_leader.txt b/testdata/confchange_v1_remove_leader.txt
index 8c4c7f91..1de8d98f 100644
--- a/testdata/confchange_v1_remove_leader.txt
+++ b/testdata/confchange_v1_remove_leader.txt
@@ -23,9 +23,9 @@ ok
 
 raft-state
 ----
-1: StateLeader (Voter)
-2: StateFollower (Voter)
-3: StateFollower (Voter)
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
 
 # Start removing n1.
 propose-conf-change 1 v1=true
@@ -35,9 +35,9 @@ ok
 
 raft-state
 ----
-1: StateLeader (Voter)
-2: StateFollower (Voter)
-3: StateFollower (Voter)
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
 
 # Propose an extra entry which will be sent out together with the conf change.
 propose 1 foo
@@ -109,9 +109,9 @@ stabilize 1
 
 raft-state
 ----
-1: StateLeader (Non-Voter)
-2: StateFollower (Voter)
-3: StateFollower (Voter)
+1: StateLeader (Non-Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
 
 # n2 responds, n3 doesn't yet. Quorum for 'bar' should not be reached...
 stabilize 2
@@ -244,6 +244,6 @@ stabilize
 # Just confirming the issue above - leader does not automatically step down.
 raft-state
 ----
-1: StateLeader (Non-Voter)
-2: StateFollower (Voter)
-3: StateFollower (Voter)
+1: StateLeader (Non-Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
diff --git a/testdata/confchange_v2_replace_leader.txt b/testdata/confchange_v2_replace_leader.txt
index 6bfe9fe5..27a3e1ab 100644
--- a/testdata/confchange_v2_replace_leader.txt
+++ b/testdata/confchange_v2_replace_leader.txt
@@ -29,9 +29,9 @@ ok
 
 raft-state
 ----
-1: StateLeader (Voter)
-2: StateFollower (Voter)
-3: StateFollower (Voter)
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
 
 log-level info
 ----
@@ -168,10 +168,10 @@ INFO 1 sends MsgTimeoutNow to 4 immediately as 4 already has up-to-date log
 # Leadership transfer wasn't processed yet.
 raft-state
 ----
-1: StateLeader (Voter)
-2: StateFollower (Voter)
-3: StateFollower (Voter)
-4: StateFollower (Voter)
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
+4: StateFollower (Voter) Term:1 Lead:1
 
 # Leadership transfer is happening here.
 stabilize
@@ -328,10 +328,10 @@ stabilize
 # Leadership transfer succeeded.
 raft-state
 ----
-1: StateFollower (Voter)
-2: StateFollower (Voter)
-3: StateFollower (Voter)
-4: StateLeader (Voter)
+1: StateFollower (Voter) Term:2 Lead:4
+2: StateFollower (Voter) Term:2 Lead:4
+3: StateFollower (Voter) Term:2 Lead:4
+4: StateLeader (Voter) Term:2 Lead:4
 
 # n4 will propose a transition out of the joint config.
 propose-conf-change 4
@@ -426,10 +426,10 @@ stabilize
 # n1 is out of the configuration.
 raft-state
 ----
-1: StateFollower (Non-Voter)
-2: StateFollower (Voter)
-3: StateFollower (Voter)
-4: StateLeader (Voter)
+1: StateFollower (Non-Voter) Term:2 Lead:4
+2: StateFollower (Voter) Term:2 Lead:4
+3: StateFollower (Voter) Term:2 Lead:4
+4: StateLeader (Voter) Term:2 Lead:4
 
 # Make sure n1 cannot campaign to become leader.
 campaign 1

From 115946606301da0fcf300f8790e847d641699225 Mon Sep 17 00:00:00 2001
From: Erik Grinaker <grinaker@cockroachlabs.com>
Date: Fri, 16 Jun 2023 17:41:42 +0000
Subject: [PATCH 3/3] add `ForgetLeader`

This patch adds `ForgetLeader()`, which causes a follower to forget its
current leader, changing it to None. It remains a leaderless follower in
the current term, without campaigning.

This is particularly useful with PreVote+CheckQuorum, if the caller has
strong reason to believe the leader is dead, since it will grant
prevotes but also revert to follower if it hears from the leader. A
quorum of such leaderless followers can thus allow a pre-candidate to
hold an election if they believe the leader to be dead.

Signed-off-by: Erik Grinaker <grinaker@cockroachlabs.com>
---
 node.go                                       |  30 +++
 raft.go                                       |  11 +
 raftpb/raft.pb.go                             | 141 ++++++-----
 raftpb/raft.proto                             |   1 +
 rafttest/interaction_env_handler.go           |   7 +
 rafttest/interaction_env_handler_add_nodes.go |   9 +
 .../interaction_env_handler_forget_leader.go  |  32 +++
 rawnode.go                                    |   6 +
 rawnode_test.go                               |   3 +
 testdata/forget_leader.txt                    | 192 ++++++++++++++
 .../forget_leader_prevote_checkquorum.txt     | 235 ++++++++++++++++++
 .../forget_leader_read_only_lease_based.txt   |  30 +++
 12 files changed, 628 insertions(+), 69 deletions(-)
 create mode 100644 rafttest/interaction_env_handler_forget_leader.go
 create mode 100644 testdata/forget_leader.txt
 create mode 100644 testdata/forget_leader_prevote_checkquorum.txt
 create mode 100644 testdata/forget_leader_read_only_lease_based.txt

diff --git a/node.go b/node.go
index 9c53aed2..fe8f8dee 100644
--- a/node.go
+++ b/node.go
@@ -189,6 +189,32 @@ type Node interface {
 	// TransferLeadership attempts to transfer leadership to the given transferee.
 	TransferLeadership(ctx context.Context, lead, transferee uint64)
 
+	// ForgetLeader forgets a follower's current leader, changing it to None. It
+	// remains a leaderless follower in the current term, without campaigning.
+	//
+	// This is useful with PreVote+CheckQuorum, where followers will normally not
+	// grant pre-votes if they've heard from the leader in the past election
+	// timeout interval. Leaderless followers can grant pre-votes immediately, so
+	// if a quorum of followers have strong reason to believe the leader is dead
+	// (for example via a side-channel or external failure detector) and forget it
+	// then they can elect a new leader immediately, without waiting out the
+	// election timeout. They will also revert to normal followers if they hear
+	// from the leader again, or transition to candidates on an election timeout.
+	//
+	// For example, consider a three-node cluster where 1 is the leader and 2+3
+	// have just received a heartbeat from it. If 2 and 3 believe the leader has
+	// now died (maybe they know that an orchestration system shut down 1's VM),
+	// we can instruct 2 to forget the leader and 3 to campaign. 2 will then be
+	// able to grant 3's pre-vote and elect 3 as leader immediately (normally 2
+	// would reject the vote until an election timeout passes because it has heard
+	// from the leader recently). However, 3 can not campaign unilaterally, a
+	// quorum have to agree that the leader is dead, which avoids disrupting the
+	// leader if individual nodes are wrong about it being dead.
+	//
+	// This does nothing with ReadOnlyLeaseBased, since it would allow a new
+	// leader to be elected without the old leader knowing.
+	ForgetLeader(ctx context.Context) error
+
 	// ReadIndex request a read state. The read state will be set in the ready.
 	// Read state has a read index. Once the application advances further than the read
 	// index, any linearizable read requests issued before the read request can be
@@ -575,6 +601,10 @@ func (n *node) TransferLeadership(ctx context.Context, lead, transferee uint64)
 	}
 }
 
+func (n *node) ForgetLeader(ctx context.Context) error {
+	return n.step(ctx, pb.Message{Type: pb.MsgForgetLeader})
+}
+
 func (n *node) ReadIndex(ctx context.Context, rctx []byte) error {
 	return n.step(ctx, pb.Message{Type: pb.MsgReadIndex, Entries: []pb.Entry{{Data: rctx}}})
 }
diff --git a/raft.go b/raft.go
index 535889ea..63b4e08c 100644
--- a/raft.go
+++ b/raft.go
@@ -1284,6 +1284,8 @@ func stepLeader(r *raft, m pb.Message) error {
 		sendMsgReadIndexResponse(r, m)
 
 		return nil
+	case pb.MsgForgetLeader:
+		return nil // noop on leader
 	}
 
 	// All other message types require a progress for m.From (pr).
@@ -1661,6 +1663,15 @@ func stepFollower(r *raft, m pb.Message) error {
 		}
 		m.To = r.lead
 		r.send(m)
+	case pb.MsgForgetLeader:
+		if r.readOnly.option == ReadOnlyLeaseBased {
+			r.logger.Error("ignoring MsgForgetLeader due to ReadOnlyLeaseBased")
+			return nil
+		}
+		if r.lead != None {
+			r.logger.Infof("%x forgetting leader %x at term %d", r.id, r.lead, r.Term)
+			r.lead = None
+		}
 	case pb.MsgTimeoutNow:
 		r.logger.Infof("%x [term %d] received MsgTimeoutNow from %x and starts an election to get leadership.", r.id, r.Term, m.From)
 		// Leadership transfers never use pre-vote even if r.preVote is true; we
diff --git a/raftpb/raft.pb.go b/raftpb/raft.pb.go
index 14802639..7dcdef0c 100644
--- a/raftpb/raft.pb.go
+++ b/raftpb/raft.pb.go
@@ -95,6 +95,7 @@ const (
 	MsgStorageAppendResp MessageType = 20
 	MsgStorageApply      MessageType = 21
 	MsgStorageApplyResp  MessageType = 22
+	MsgForgetLeader      MessageType = 23
 )
 
 var MessageType_name = map[int32]string{
@@ -121,6 +122,7 @@ var MessageType_name = map[int32]string{
 	20: "MsgStorageAppendResp",
 	21: "MsgStorageApply",
 	22: "MsgStorageApplyResp",
+	23: "MsgForgetLeader",
 }
 
 var MessageType_value = map[string]int32{
@@ -147,6 +149,7 @@ var MessageType_value = map[string]int32{
 	"MsgStorageAppendResp": 20,
 	"MsgStorageApply":      21,
 	"MsgStorageApplyResp":  22,
+	"MsgForgetLeader":      23,
 }
 
 func (x MessageType) Enum() *MessageType {
@@ -726,76 +729,76 @@ func init() {
 func init() { proto.RegisterFile("raft.proto", fileDescriptor_b042552c306ae59b) }
 
 var fileDescriptor_b042552c306ae59b = []byte{
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+	0xef, 0x2b, 0xb8, 0xfb, 0xbb, 0x0d, 0xa0, 0x44, 0x6f, 0x9f, 0x13, 0x16, 0x50, 0xfc, 0x89, 0xb9,
+	0x0b, 0x8e, 0xbe, 0x0b, 0x8f, 0x8b, 0x77, 0x3b, 0x61, 0xdc, 0xbb, 0x0e, 0x2f, 0xa0, 0xc2, 0xb8,
+	0x4f, 0x4f, 0x42, 0xdf, 0x98, 0xd2, 0x54, 0xc1, 0xdb, 0xb7, 0x4f, 0xcb, 0x07, 0xdc, 0xa7, 0x7b,
+	0x3b, 0xc3, 0xb2, 0x0a, 0xef, 0xf9, 0xd8, 0xcb, 0x47, 0x9a, 0x3c, 0x34, 0xd9, 0x30, 0x57, 0xc1,
+	0x09, 0x7d, 0x33, 0x08, 0x30, 0xa7, 0x9d, 0xbd, 0x9d, 0xa1, 0x13, 0xfa, 0xdd, 0x09, 0xa0, 0xbc,
+	0xf8, 0x61, 0xc8, 0x82, 0x71, 0x2e, 0xd2, 0xfe, 0x3f, 0x22, 0x9d, 0xf7, 0x89, 0xec, 0xfe, 0x61,
+	0x43, 0x23, 0xcf, 0x73, 0xdc, 0xc7, 0x5b, 0x00, 0x52, 0x10, 0x16, 0x87, 0x32, 0xe4, 0xcc, 0x54,
+	0x5c, 0x7b, 0xa0, 0x62, 0xc6, 0x49, 0x3f, 0xe6, 0xfc, 0x14, 0xfe, 0x1c, 0x2a, 0x23, 0xcd, 0x4a,
+	0x26, 0x5e, 0x78, 0xa7, 0xe6, 0x5b, 0x4b, 0xaf, 0xad, 0xa1, 0x17, 0x3d, 0x2b, 0xcd, 0x78, 0xb6,
+	0xbe, 0x0b, 0xb5, 0xec, 0x31, 0xc7, 0x4b, 0x50, 0xd7, 0x9b, 0x03, 0x2e, 0x26, 0x64, 0x8c, 0x2c,
+	0xbc, 0x02, 0x4b, 0x1a, 0xc8, 0xf3, 0x23, 0x1b, 0x3f, 0x82, 0xe5, 0x39, 0xf0, 0xb8, 0x8f, 0x9c,
+	0xf5, 0xbf, 0x4a, 0x50, 0x2f, 0xbc, 0x75, 0x18, 0xa0, 0x3c, 0x88, 0x83, 0xdd, 0x69, 0x84, 0x2c,
+	0x5c, 0x87, 0xca, 0x20, 0x0e, 0xb6, 0x28, 0x91, 0xc8, 0x36, 0x9b, 0xd7, 0x82, 0x47, 0xc8, 0x31,
+	0xac, 0xcd, 0x28, 0x42, 0x25, 0xdc, 0x04, 0x48, 0xd6, 0x43, 0x1a, 0x47, 0xc8, 0x35, 0xc4, 0x63,
+	0x2e, 0x29, 0x5a, 0x50, 0xda, 0xcc, 0x46, 0x47, 0xcb, 0x26, 0xaa, 0x5e, 0x0f, 0x54, 0xc1, 0x08,
+	0x1a, 0xaa, 0x18, 0x25, 0x42, 0x9e, 0xaa, 0x2a, 0x55, 0xdc, 0x02, 0x54, 0x44, 0xf4, 0xa1, 0x1a,
+	0xc6, 0xd0, 0x1c, 0xc4, 0xc1, 0x1b, 0x26, 0x28, 0x19, 0x9d, 0x93, 0xd3, 0x31, 0x45, 0x80, 0x97,
+	0x61, 0xd1, 0x24, 0x52, 0x37, 0x6e, 0x1a, 0xa3, 0xba, 0xa1, 0x6d, 0x9f, 0xd3, 0xd1, 0x0f, 0xdf,
+	0x4c, 0xb9, 0x98, 0x4e, 0x50, 0x43, 0xb5, 0x3d, 0x88, 0x03, 0x3d, 0xa0, 0x33, 0x2a, 0xf6, 0x29,
+	0xf1, 0xa9, 0x40, 0x8b, 0xe6, 0xf4, 0x51, 0x38, 0xa1, 0x7c, 0x2a, 0x0f, 0xf8, 0x8f, 0xa8, 0x69,
+	0xc4, 0x0c, 0x29, 0xf1, 0xf5, 0x4f, 0x14, 0x2d, 0x19, 0x31, 0x19, 0xa2, 0xc5, 0x20, 0xd3, 0xef,
+	0x6b, 0x41, 0x75, 0x8b, 0xcb, 0xa6, 0xaa, 0xd9, 0x6b, 0x0e, 0x36, 0x27, 0x0f, 0x25, 0x17, 0x24,
+	0xa0, 0x9b, 0x51, 0x44, 0x99, 0x8f, 0x56, 0xb0, 0x07, 0xad, 0x79, 0x54, 0xf3, 0x5b, 0x6a, 0x62,
+	0x33, 0x91, 0xf1, 0x15, 0x7a, 0x84, 0x9f, 0xc0, 0xca, 0x1c, 0xa8, 0xd9, 0x8f, 0x0d, 0xfb, 0x4b,
+	0x2e, 0x02, 0x2a, 0x4d, 0x47, 0x4f, 0xd6, 0x7f, 0xb1, 0xa1, 0xf5, 0xd0, 0x17, 0x89, 0xd7, 0xc0,
+	0x7b, 0x08, 0xdf, 0x9c, 0x4a, 0x8e, 0x2c, 0xfc, 0x21, 0x7c, 0xf0, 0x50, 0xf4, 0x2b, 0x1e, 0x32,
+	0xb9, 0x37, 0x89, 0xc6, 0xe1, 0x28, 0x54, 0xd3, 0x7f, 0x1f, 0xed, 0xd5, 0xa5, 0xa1, 0x39, 0xeb,
+	0x57, 0xd0, 0x9c, 0xbd, 0x87, 0xca, 0xff, 0x1c, 0xd9, 0xf4, 0x7d, 0x75, 0xe3, 0x90, 0xa5, 0xac,
+	0xc8, 0xe1, 0x21, 0x9d, 0xf0, 0x0b, 0xaa, 0x23, 0xf6, 0x6c, 0xe4, 0x4d, 0xe4, 0x13, 0x99, 0x44,
+	0x9c, 0xd9, 0x46, 0x36, 0x7d, 0x7f, 0x3f, 0x79, 0xee, 0x74, 0xb4, 0xb4, 0xf5, 0xfc, 0xfa, 0x5d,
+	0xdb, 0xba, 0x79, 0xd7, 0xb6, 0xae, 0x6f, 0xdb, 0xf6, 0xcd, 0x6d, 0xdb, 0xfe, 0xe7, 0xb6, 0x6d,
+	0xff, 0x7a, 0xd7, 0xb6, 0x7e, 0xbb, 0x6b, 0x5b, 0x37, 0x77, 0x6d, 0xeb, 0xef, 0xbb, 0xb6, 0xf5,
+	0x5f, 0x00, 0x00, 0x00, 0xff, 0xff, 0x67, 0x2b, 0x47, 0x0c, 0x83, 0x09, 0x00, 0x00,
 }
 
 func (m *Entry) Marshal() (dAtA []byte, err error) {
diff --git a/raftpb/raft.proto b/raftpb/raft.proto
index a70f736a..a8598ee5 100644
--- a/raftpb/raft.proto
+++ b/raftpb/raft.proto
@@ -62,6 +62,7 @@ enum MessageType {
 	MsgStorageAppendResp = 20;
 	MsgStorageApply      = 21;
 	MsgStorageApplyResp  = 22;
+	MsgForgetLeader      = 23;
 	// NOTE: when adding new message types, remember to update the isLocalMsg and
 	// isResponseMsg arrays in raft/util.go and update the corresponding tests in
 	// raft/util_test.go.
diff --git a/rafttest/interaction_env_handler.go b/rafttest/interaction_env_handler.go
index 3c1ddbfa..c4c84fe6 100644
--- a/rafttest/interaction_env_handler.go
+++ b/rafttest/interaction_env_handler.go
@@ -142,6 +142,13 @@ func (env *InteractionEnv) Handle(t *testing.T, d datadriven.TestData) string {
 		//
 		// transfer-leadership from=1 to=4
 		err = env.handleTransferLeadership(t, d)
+	case "forget-leader":
+		// Forgets the current leader of the given node.
+		//
+		// Example:
+		//
+		// forget-leader 1
+		err = env.handleForgetLeader(t, d)
 	case "propose":
 		// Propose an entry.
 		//
diff --git a/rafttest/interaction_env_handler_add_nodes.go b/rafttest/interaction_env_handler_add_nodes.go
index 3f2dd629..1c3ed773 100644
--- a/rafttest/interaction_env_handler_add_nodes.go
+++ b/rafttest/interaction_env_handler_add_nodes.go
@@ -54,6 +54,15 @@ func (env *InteractionEnv) handleAddNodes(t *testing.T, d datadriven.TestData) e
 				arg.Scan(t, i, &cfg.PreVote)
 			case "checkquorum":
 				arg.Scan(t, i, &cfg.CheckQuorum)
+			case "read-only":
+				switch arg.Vals[i] {
+				case "safe":
+					cfg.ReadOnlyOption = raft.ReadOnlySafe
+				case "lease-based":
+					cfg.ReadOnlyOption = raft.ReadOnlyLeaseBased
+				default:
+					return fmt.Errorf("invalid read-only option %q", arg.Vals[i])
+				}
 			}
 		}
 	}
diff --git a/rafttest/interaction_env_handler_forget_leader.go b/rafttest/interaction_env_handler_forget_leader.go
new file mode 100644
index 00000000..8884e0d6
--- /dev/null
+++ b/rafttest/interaction_env_handler_forget_leader.go
@@ -0,0 +1,32 @@
+// Copyright 2023 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package rafttest
+
+import (
+	"testing"
+
+	"github.com/cockroachdb/datadriven"
+)
+
+func (env *InteractionEnv) handleForgetLeader(t *testing.T, d datadriven.TestData) error {
+	idx := firstAsNodeIdx(t, d)
+	env.ForgetLeader(t, idx)
+	return nil
+}
+
+// ForgetLeader makes the follower at the given index forget its leader.
+func (env *InteractionEnv) ForgetLeader(t *testing.T, idx int) {
+	env.Nodes[idx].ForgetLeader()
+}
diff --git a/rawnode.go b/rawnode.go
index bad7ae98..a474f97c 100644
--- a/rawnode.go
+++ b/rawnode.go
@@ -544,6 +544,12 @@ func (rn *RawNode) TransferLeader(transferee uint64) {
 	_ = rn.raft.Step(pb.Message{Type: pb.MsgTransferLeader, From: transferee})
 }
 
+// ForgetLeader forgets a follower's current leader, changing it to None.
+// See (Node).ForgetLeader for details.
+func (rn *RawNode) ForgetLeader() error {
+	return rn.raft.Step(pb.Message{Type: pb.MsgForgetLeader})
+}
+
 // ReadIndex requests a read state. The read state will be set in ready.
 // Read State has a read index. Once the application advances further than the read
 // index, any linearizable read requests issued before the read request can be
diff --git a/rawnode_test.go b/rawnode_test.go
index 553d74fd..e570be3b 100644
--- a/rawnode_test.go
+++ b/rawnode_test.go
@@ -41,6 +41,9 @@ func (a *rawNodeAdapter) TransferLeadership(ctx context.Context, lead, transfere
 	a.RawNode.TransferLeader(transferee)
 }
 
+// ForgetLeader takes a context, RawNode doesn't need it.
+func (a *rawNodeAdapter) ForgetLeader(context.Context) error { return a.RawNode.ForgetLeader() }
+
 // Stop when node has a goroutine, RawNode doesn't need this.
 func (a *rawNodeAdapter) Stop() {}
 
diff --git a/testdata/forget_leader.txt b/testdata/forget_leader.txt
new file mode 100644
index 00000000..a674b346
--- /dev/null
+++ b/testdata/forget_leader.txt
@@ -0,0 +1,192 @@
+log-level none
+----
+ok
+
+add-nodes 4 voters=(1,2,3) learners=(4) index=10
+----
+ok
+
+campaign 1
+----
+ok
+
+stabilize
+----
+ok
+
+log-level debug
+----
+ok
+
+# ForgetLeader is a noop on the leader.
+forget-leader 1
+----
+ok
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
+4: StateFollower (Non-Voter) Term:1 Lead:1
+
+# ForgetLeader causes a follower to forget its leader, but remain in the current
+# term. It's a noop if it's called again.
+forget-leader 2
+----
+INFO 2 forgetting leader 1 at term 1
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:0
+3: StateFollower (Voter) Term:1 Lead:1
+4: StateFollower (Non-Voter) Term:1 Lead:1
+
+forget-leader 2
+----
+ok
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:0
+3: StateFollower (Voter) Term:1 Lead:1
+4: StateFollower (Non-Voter) Term:1 Lead:1
+
+# ForgetLeader also works on learners.
+forget-leader 4
+----
+INFO 4 forgetting leader 1 at term 1
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:0
+3: StateFollower (Voter) Term:1 Lead:1
+4: StateFollower (Non-Voter) Term:1 Lead:0
+
+# When receiving a heartbeat from the leader, they revert to followers.
+tick-heartbeat 1
+----
+ok
+
+stabilize
+----
+> 1 handling Ready
+  Ready MustSync=false:
+  Messages:
+  1->2 MsgHeartbeat Term:1 Log:0/0 Commit:11
+  1->3 MsgHeartbeat Term:1 Log:0/0 Commit:11
+  1->4 MsgHeartbeat Term:1 Log:0/0 Commit:11
+> 2 handling Ready
+  Ready MustSync=false:
+  Lead:0 State:StateFollower
+> 4 handling Ready
+  Ready MustSync=false:
+  Lead:0 State:StateFollower
+> 2 receiving messages
+  1->2 MsgHeartbeat Term:1 Log:0/0 Commit:11
+> 3 receiving messages
+  1->3 MsgHeartbeat Term:1 Log:0/0 Commit:11
+> 4 receiving messages
+  1->4 MsgHeartbeat Term:1 Log:0/0 Commit:11
+> 2 handling Ready
+  Ready MustSync=false:
+  Lead:1 State:StateFollower
+  Messages:
+  2->1 MsgHeartbeatResp Term:1 Log:0/0
+> 3 handling Ready
+  Ready MustSync=false:
+  Messages:
+  3->1 MsgHeartbeatResp Term:1 Log:0/0
+> 4 handling Ready
+  Ready MustSync=false:
+  Lead:1 State:StateFollower
+  Messages:
+  4->1 MsgHeartbeatResp Term:1 Log:0/0
+> 1 receiving messages
+  2->1 MsgHeartbeatResp Term:1 Log:0/0
+  3->1 MsgHeartbeatResp Term:1 Log:0/0
+  4->1 MsgHeartbeatResp Term:1 Log:0/0
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
+4: StateFollower (Non-Voter) Term:1 Lead:1
+
+# ForgetLeader is a noop on candidates.
+campaign 3
+----
+INFO 3 is starting a new election at term 1
+INFO 3 became candidate at term 2
+INFO 3 [logterm: 1, index: 11] sent MsgVote request to 1 at term 2
+INFO 3 [logterm: 1, index: 11] sent MsgVote request to 2 at term 2
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateCandidate (Voter) Term:2 Lead:0
+4: StateFollower (Non-Voter) Term:1 Lead:1
+
+forget-leader 3
+----
+ok
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateCandidate (Voter) Term:2 Lead:0
+4: StateFollower (Non-Voter) Term:1 Lead:1
+
+stabilize log-level=none
+----
+ok
+
+raft-state
+----
+1: StateFollower (Voter) Term:2 Lead:3
+2: StateFollower (Voter) Term:2 Lead:3
+3: StateLeader (Voter) Term:2 Lead:3
+4: StateFollower (Non-Voter) Term:2 Lead:3
+
+# ForgetLeader shouldn't affect the election timeout: if a follower
+# forgets the leader 1 tick before the election timeout fires, it
+# will still campaign on the next tick.
+set-randomized-election-timeout 2 timeout=3
+----
+ok
+
+tick-heartbeat 2
+----
+ok
+
+tick-heartbeat 2
+----
+ok
+
+forget-leader 2
+----
+INFO 2 forgetting leader 3 at term 2
+
+tick-heartbeat 2
+----
+INFO 2 is starting a new election at term 2
+INFO 2 became candidate at term 3
+INFO 2 [logterm: 2, index: 12] sent MsgVote request to 1 at term 3
+INFO 2 [logterm: 2, index: 12] sent MsgVote request to 3 at term 3
+
+stabilize log-level=none
+----
+ok
+
+raft-state
+----
+1: StateFollower (Voter) Term:3 Lead:2
+2: StateLeader (Voter) Term:3 Lead:2
+3: StateFollower (Voter) Term:3 Lead:2
+4: StateFollower (Non-Voter) Term:3 Lead:2
diff --git a/testdata/forget_leader_prevote_checkquorum.txt b/testdata/forget_leader_prevote_checkquorum.txt
new file mode 100644
index 00000000..9b3b80ff
--- /dev/null
+++ b/testdata/forget_leader_prevote_checkquorum.txt
@@ -0,0 +1,235 @@
+# Tests that a follower with PreVote+CheckQuorum can forget the leader, allowing
+# it to grant prevotes despite having heard from the leader recently.
+#
+# Also tests that forgetting the leader still won't grant prevotes to a
+# replica that isn't up-to-date.
+log-level none
+----
+ok
+
+add-nodes 3 voters=(1,2,3) index=10 prevote=true checkquorum=true
+----
+ok
+
+campaign 1
+----
+ok
+
+stabilize
+----
+ok
+
+log-level debug
+----
+ok
+
+# If 3 attempts to campaign, 2 rejects it because it has a leader.
+campaign 3
+----
+INFO 3 is starting a new election at term 1
+INFO 3 became pre-candidate at term 1
+INFO 3 [logterm: 1, index: 11] sent MsgPreVote request to 1 at term 1
+INFO 3 [logterm: 1, index: 11] sent MsgPreVote request to 2 at term 1
+
+stabilize 3
+----
+> 3 handling Ready
+  Ready MustSync=false:
+  Lead:0 State:StatePreCandidate
+  Messages:
+  3->1 MsgPreVote Term:2 Log:1/11
+  3->2 MsgPreVote Term:2 Log:1/11
+  INFO 3 received MsgPreVoteResp from 3 at term 1
+  INFO 3 has received 1 MsgPreVoteResp votes and 0 vote rejections
+
+deliver-msgs 1 2
+----
+3->1 MsgPreVote Term:2 Log:1/11
+INFO 1 [logterm: 1, index: 11, vote: 1] ignored MsgPreVote from 3 [logterm: 1, index: 11] at term 1: lease is not expired (remaining ticks: 3)
+3->2 MsgPreVote Term:2 Log:1/11
+INFO 2 [logterm: 1, index: 11, vote: 1] ignored MsgPreVote from 3 [logterm: 1, index: 11] at term 1: lease is not expired (remaining ticks: 3)
+
+# Make 1 assert leadership over 3 again.
+tick-heartbeat 1
+----
+ok
+
+stabilize
+----
+> 1 handling Ready
+  Ready MustSync=false:
+  Messages:
+  1->2 MsgHeartbeat Term:1 Log:0/0 Commit:11
+  1->3 MsgHeartbeat Term:1 Log:0/0 Commit:11
+> 2 receiving messages
+  1->2 MsgHeartbeat Term:1 Log:0/0 Commit:11
+> 3 receiving messages
+  1->3 MsgHeartbeat Term:1 Log:0/0 Commit:11
+  INFO 3 became follower at term 1
+> 2 handling Ready
+  Ready MustSync=false:
+  Messages:
+  2->1 MsgHeartbeatResp Term:1 Log:0/0
+> 3 handling Ready
+  Ready MustSync=false:
+  Lead:1 State:StateFollower
+  Messages:
+  3->1 MsgHeartbeatResp Term:1 Log:0/0
+> 1 receiving messages
+  2->1 MsgHeartbeatResp Term:1 Log:0/0
+  3->1 MsgHeartbeatResp Term:1 Log:0/0
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1
+
+# If 2 forgets the leader, then 3 can obtain prevotes and hold an election
+# despite 2 having heard from the leader recently.
+forget-leader 2
+----
+INFO 2 forgetting leader 1 at term 1
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:0
+3: StateFollower (Voter) Term:1 Lead:1
+
+campaign 3
+----
+INFO 3 is starting a new election at term 1
+INFO 3 became pre-candidate at term 1
+INFO 3 [logterm: 1, index: 11] sent MsgPreVote request to 1 at term 1
+INFO 3 [logterm: 1, index: 11] sent MsgPreVote request to 2 at term 1
+
+stabilize 3
+----
+> 3 handling Ready
+  Ready MustSync=false:
+  Lead:0 State:StatePreCandidate
+  Messages:
+  3->1 MsgPreVote Term:2 Log:1/11
+  3->2 MsgPreVote Term:2 Log:1/11
+  INFO 3 received MsgPreVoteResp from 3 at term 1
+  INFO 3 has received 1 MsgPreVoteResp votes and 0 vote rejections
+
+stabilize 2
+----
+> 2 handling Ready
+  Ready MustSync=false:
+  Lead:0 State:StateFollower
+> 2 receiving messages
+  3->2 MsgPreVote Term:2 Log:1/11
+  INFO 2 [logterm: 1, index: 11, vote: 1] cast MsgPreVote for 3 [logterm: 1, index: 11] at term 1
+> 2 handling Ready
+  Ready MustSync=false:
+  Messages:
+  2->3 MsgPreVoteResp Term:2 Log:0/0
+
+stabilize 3
+----
+> 3 receiving messages
+  2->3 MsgPreVoteResp Term:2 Log:0/0
+  INFO 3 received MsgPreVoteResp from 2 at term 1
+  INFO 3 has received 2 MsgPreVoteResp votes and 0 vote rejections
+  INFO 3 became candidate at term 2
+  INFO 3 [logterm: 1, index: 11] sent MsgVote request to 1 at term 2
+  INFO 3 [logterm: 1, index: 11] sent MsgVote request to 2 at term 2
+> 3 handling Ready
+  Ready MustSync=true:
+  Lead:0 State:StateCandidate
+  HardState Term:2 Vote:3 Commit:11
+  Messages:
+  3->1 MsgVote Term:2 Log:1/11
+  3->2 MsgVote Term:2 Log:1/11
+  INFO 3 received MsgVoteResp from 3 at term 2
+  INFO 3 has received 1 MsgVoteResp votes and 0 vote rejections
+
+stabilize log-level=none
+----
+ok
+
+raft-state
+----
+1: StateFollower (Voter) Term:2 Lead:3
+2: StateFollower (Voter) Term:2 Lead:3
+3: StateLeader (Voter) Term:2 Lead:3
+
+# Test that forgetting the leader still won't grant prevotes if the candidate
+# isn't up-to-date. We first replicate a proposal on 3 and 2.
+propose 3 prop_1
+----
+ok
+
+stabilize 3
+----
+> 3 handling Ready
+  Ready MustSync=true:
+  Entries:
+  2/13 EntryNormal "prop_1"
+  Messages:
+  3->1 MsgApp Term:2 Log:2/12 Commit:12 Entries:[2/13 EntryNormal "prop_1"]
+  3->2 MsgApp Term:2 Log:2/12 Commit:12 Entries:[2/13 EntryNormal "prop_1"]
+
+stabilize 2
+----
+> 2 receiving messages
+  3->2 MsgApp Term:2 Log:2/12 Commit:12 Entries:[2/13 EntryNormal "prop_1"]
+> 2 handling Ready
+  Ready MustSync=true:
+  Entries:
+  2/13 EntryNormal "prop_1"
+  Messages:
+  2->3 MsgAppResp Term:2 Log:0/13
+
+forget-leader 2
+----
+INFO 2 forgetting leader 3 at term 2
+
+# 1 is now behind on its log. It tries to campaign, but fails.
+raft-log 1
+----
+1/11 EntryNormal ""
+2/12 EntryNormal ""
+
+campaign 1
+----
+INFO 1 is starting a new election at term 2
+INFO 1 became pre-candidate at term 2
+INFO 1 [logterm: 2, index: 12] sent MsgPreVote request to 2 at term 2
+INFO 1 [logterm: 2, index: 12] sent MsgPreVote request to 3 at term 2
+
+process-ready 1
+----
+Ready MustSync=false:
+Lead:0 State:StatePreCandidate
+Messages:
+1->2 MsgPreVote Term:3 Log:2/12
+1->3 MsgPreVote Term:3 Log:2/12
+INFO 1 received MsgPreVoteResp from 1 at term 2
+INFO 1 has received 1 MsgPreVoteResp votes and 0 vote rejections
+
+stabilize 2
+----
+> 2 handling Ready
+  Ready MustSync=false:
+  Lead:0 State:StateFollower
+> 2 receiving messages
+  1->2 MsgPreVote Term:3 Log:2/12
+  INFO 2 [logterm: 2, index: 13, vote: 3] rejected MsgPreVote from 1 [logterm: 2, index: 12] at term 2
+> 2 handling Ready
+  Ready MustSync=false:
+  Messages:
+  2->1 MsgPreVoteResp Term:2 Log:0/0 Rejected (Hint: 0)
+
+stabilize log-level=none
+----
+ok
+
+raft-state
+----
+1: StateFollower (Voter) Term:2 Lead:3
+2: StateFollower (Voter) Term:2 Lead:3
+3: StateLeader (Voter) Term:2 Lead:3
diff --git a/testdata/forget_leader_read_only_lease_based.txt b/testdata/forget_leader_read_only_lease_based.txt
new file mode 100644
index 00000000..4d4bd188
--- /dev/null
+++ b/testdata/forget_leader_read_only_lease_based.txt
@@ -0,0 +1,30 @@
+log-level none
+----
+ok
+
+add-nodes 3 voters=(1,2,3) index=10 checkquorum=true read-only=lease-based
+----
+ok
+
+campaign 1
+----
+ok
+
+stabilize
+----
+ok
+
+log-level debug
+----
+ok
+
+# ForgetLeader fails with lease-based reads, as it's not safe.
+forget-leader 2
+----
+ERROR ignoring MsgForgetLeader due to ReadOnlyLeaseBased
+
+raft-state
+----
+1: StateLeader (Voter) Term:1 Lead:1
+2: StateFollower (Voter) Term:1 Lead:1
+3: StateFollower (Voter) Term:1 Lead:1