feat: add disable_proposal_forwarding config params (#552)

Signed-off-by: Dat Tien Nguyen <[email protected]>

harness/tests/integration_cases/test_raw_node.rs

@@ -1876,6 +1876,77 @@ fn test_committed_entries_pagination_after_restart() {
     }
 }
 
+#[test]
+fn test_disable_proposal_forwarding() {
+    let l = default_logger();
+
+    let n1 = new_test_raft_with_config(
+        &Config {
+            id: 1,
+            heartbeat_tick: 1,
+            election_tick: 10,
+            disable_proposal_forwarding: false,
+            ..Default::default()
+        },
+        MemStorage::new_with_conf_state((vec![1, 2, 3], vec![])),
+        &l,
+    );
+
+    let n2 = new_test_raft_with_config(
+        &Config {
+            id: 2,
+            heartbeat_tick: 1,
+            election_tick: 10,
+            disable_proposal_forwarding: false,
+            ..Default::default()
+        },
+        MemStorage::new_with_conf_state((vec![1, 2, 3], vec![])),
+        &l,
+    );
+
+    let n3 = new_test_raft_with_config(
+        &Config {
+            id: 3,
+            heartbeat_tick: 1,
+            election_tick: 10,
+            disable_proposal_forwarding: true,
+            ..Default::default()
+        },
+        MemStorage::new_with_conf_state((vec![1, 2, 3], vec![])),
+        &l,
+    );
+
+    let mut network = Network::new(vec![Some(n1), Some(n2), Some(n3)], &l);
+
+    // node 1 starts campaign to become leader.
+    network.send(vec![new_message(1, 1, MessageType::MsgHup, 0)]);
+
+    // send proposal to n2(follower) where DisableProposalForwarding is false
+    assert_eq!(
+        network
+            .peers
+            .get_mut(&2)
+            .unwrap()
+            .step(new_message(2, 2, MessageType::MsgPropose, 1)),
+        Ok(())
+    );
+
+    // verify n2(follower) does forward the proposal when DisableProposalForwarding is false
+    assert_eq!(network.peers.get(&2).unwrap().msgs.len(), 1);
+
+    // send proposal to n3(follower) where DisableProposalForwarding is true
+    assert_eq!(
+        network
+            .peers
+            .get_mut(&3)
+            .unwrap()
+            .step(new_message(3, 3, MessageType::MsgPropose, 1)),
+        Err(Error::ProposalDropped)
+    );
+
+    assert!(network.peers.get(&3).unwrap().msgs.is_empty());
+}
+
 #[derive(Default)]
 struct IgnoreSizeHintMemStorage {
     inner: MemStorage,

src/config.rs

@@ -102,6 +102,9 @@ pub struct Config {
     /// Maximum raft log number that can be applied after commit but before persist.
     /// The default value is 0, which means apply after both commit and persist.
     pub max_apply_unpersisted_log_limit: u64,
+
+    /// If enable, followers will not forward proposal to leader.
+    pub disable_proposal_forwarding: bool,
 }
 
 impl Default for Config {
@@ -125,6 +128,7 @@ impl Default for Config {
             max_uncommitted_size: NO_LIMIT,
             max_committed_size_per_ready: NO_LIMIT,
             max_apply_unpersisted_log_limit: 0,
+            disable_proposal_forwarding: false,
         }
     }
 }

src/raft.rs

@@ -233,6 +233,7 @@ pub struct RaftCore<T: Storage> {
 
     skip_bcast_commit: bool,
     batch_append: bool,
+    disable_proposal_forwarding: bool,
 
     heartbeat_timeout: usize,
     election_timeout: usize,
@@ -363,6 +364,7 @@ impl<T: Storage> Raft<T> {
                     last_log_tail_index: 0,
                 },
                 max_committed_size_per_ready: c.max_committed_size_per_ready,
+                disable_proposal_forwarding: c.disable_proposal_forwarding,
             },
         };
         confchange::restore(&mut r.prs, r.r.raft_log.last_index(), conf_state)?;
@@ -2337,6 +2339,15 @@ impl<T: Storage> Raft<T> {
                         term = self.term;
                     );
                     return Err(Error::ProposalDropped);
+                } else if self.disable_proposal_forwarding {
+                    info!(
+                        self.logger,
+                        "{from} not forwarding to leader {to} at term {term}; dropping proposal",
+                        from = self.id,
+                        to = self.leader_id,
+                        term = self.term;
+                    );
+                    return Err(Error::ProposalDropped);
                 }
                 m.to = self.leader_id;
                 self.r.send(m, &mut self.msgs);