Fixed the local-cluster test case test_optimistic_confirmation_violation_detection (#27580)

* Fixed the local-cluster test case test_optimistic_confirmation_violation_detection, which is an existing test issue exposed when we disable the udp based tpu port. In the test, when we restart the node, we restarted the entry point validator. And when the gossip port of the restarted node changes, the two nodes are not able to talk to each other via gossip. I have changed the restart the logic to make the second validator the heavier node and restart it instead of the entypoint one (the first node).

* Addressed a review comment from Carl

local-cluster/tests/local_cluster.rs

@@ -1594,7 +1594,7 @@ fn test_optimistic_confirmation_violation_detection() {
     solana_logger::setup_with_default(RUST_LOG_FILTER);
     // First set up the cluster with 2 nodes
     let slots_per_epoch = 2048;
-    let node_stakes = vec![51 * DEFAULT_NODE_STAKE, 50 * DEFAULT_NODE_STAKE];
+    let node_stakes = vec![50 * DEFAULT_NODE_STAKE, 51 * DEFAULT_NODE_STAKE];
     let validator_keys: Vec<_> = vec![
         "4qhhXNTbKD1a5vxDDLZcHKj7ELNeiivtUBxn3wUK1F5VRsQVP89VUhfXqSfgiFB14GfuBgtrQ96n9NvWQADVkcCg",
         "3kHBzVwie5vTEaY6nFCPeFT8qDpoXzn7dCEioGRNBTnUDpvwnG85w8Wq63gVWpVTP8k2a8cgcWRjSXyUkEygpXWS",
@@ -1603,6 +1603,12 @@ fn test_optimistic_confirmation_violation_detection() {
     .map(|s| (Arc::new(Keypair::from_base58_string(s)), true))
     .take(node_stakes.len())
     .collect();
+
+    // Do not restart the validator which is the cluster entrypoint because its gossip port
+    // might be changed after restart resulting in the two nodes not being able to
+    // to form a cluster. The heavier validator is the second node.
+    let node_to_restart = validator_keys[1].0.pubkey();
+
     let mut config = ClusterConfig {
         cluster_lamports: DEFAULT_CLUSTER_LAMPORTS + node_stakes.iter().sum::<u64>(),
         node_stakes: node_stakes.clone(),
@@ -1617,12 +1623,11 @@ fn test_optimistic_confirmation_violation_detection() {
         ..ClusterConfig::default()
     };
     let mut cluster = LocalCluster::new(&mut config, SocketAddrSpace::Unspecified);
-    let entry_point_id = cluster.entry_point_info.id;
     // Let the nodes run for a while. Wait for validators to vote on slot `S`
     // so that the vote on `S-1` is definitely in gossip and optimistic confirmation is
     // detected on slot `S-1` for sure, then stop the heavier of the two
     // validators
-    let client = cluster.get_validator_client(&entry_point_id).unwrap();
+    let client = cluster.get_validator_client(&node_to_restart).unwrap();
     let mut prev_voted_slot = 0;
     loop {
         let last_voted_slot = client
@@ -1638,7 +1643,7 @@ fn test_optimistic_confirmation_violation_detection() {
         sleep(Duration::from_millis(100));
     }
 
-    let exited_validator_info = cluster.exit_node(&entry_point_id);
+    let exited_validator_info = cluster.exit_node(&node_to_restart);
 
     // Mark fork as dead on the heavier validator, this should make the fork effectively
     // dead, even though it was optimistically confirmed. The smaller validator should
@@ -1658,7 +1663,7 @@ fn test_optimistic_confirmation_violation_detection() {
         // on ancestors of last vote)
         // 2) Won't reset to this earlier ancestor becasue reset can only happen on same voted fork if
         // it's for the last vote slot or later
-        remove_tower(&exited_validator_info.info.ledger_path, &entry_point_id);
+        remove_tower(&exited_validator_info.info.ledger_path, &node_to_restart);
         blockstore.set_dead_slot(prev_voted_slot).unwrap();
     }
 
@@ -1668,7 +1673,7 @@ fn test_optimistic_confirmation_violation_detection() {
             .err()
             .map(|_| BufferRedirect::stderr().unwrap());
         cluster.restart_node(
-            &entry_point_id,
+            &node_to_restart,
             exited_validator_info,
             SocketAddrSpace::Unspecified,
         );
@@ -1676,7 +1681,7 @@ fn test_optimistic_confirmation_violation_detection() {
         // Wait for a root > prev_voted_slot to be set. Because the root is on a
         // different fork than `prev_voted_slot`, then optimistic confirmation is
         // violated
-        let client = cluster.get_validator_client(&entry_point_id).unwrap();
+        let client = cluster.get_validator_client(&node_to_restart).unwrap();
         loop {
             let last_root = client
                 .get_slot_with_commitment(CommitmentConfig::finalized())
@@ -1716,7 +1721,7 @@ fn test_optimistic_confirmation_violation_detection() {
     // Make sure validator still makes progress
     cluster_tests::check_for_new_roots(
         16,
-        &[cluster.get_contact_info(&entry_point_id).unwrap().clone()],
+        &[cluster.get_contact_info(&node_to_restart).unwrap().clone()],
         &cluster.connection_cache,
         "test_optimistic_confirmation_violation",
     );