[Epoch Sync] Enable epoch sync by default in configs.

chain/client/src/sync/epoch.rs

@@ -590,7 +590,7 @@ impl EpochSync {
         highest_height: BlockHeight,
         highest_height_peers: &[HighestHeightPeerInfo],
     ) -> Result<(), Error> {
-        if !self.config.enabled {
+        if self.config.disable_epoch_sync_for_bootstrapping {
             return Ok(());
         }
         let tip_height = chain.chain_store().header_head()?.height;
@@ -966,9 +966,8 @@ impl EpochSync {
 impl Handler<EpochSyncRequestMessage> for ClientActorInner {
     #[perf]
     fn handle(&mut self, msg: EpochSyncRequestMessage) {
-        if !self.client.epoch_sync.config.enabled {
-            // TODO(#11937): before we have rate limiting, don't respond to epoch sync requests
-            // unless config is enabled.
+        if self.client.epoch_sync.config.ignore_epoch_sync_network_requests {
+            // Temporary killswitch for the rare case there were issues with this network request.
             return;
         }
         let store = self.client.chain.chain_store.store().clone();

core/chain-configs/src/client_config.rs

@@ -188,16 +188,35 @@ impl SyncConfig {
 
 #[derive(serde::Serialize, serde::Deserialize, Clone, Debug)]
 pub struct EpochSyncConfig {
-    pub enabled: bool,
+    /// If true, even if the node started from genesis, it will not perform epoch sync.
+    /// There should be no reason to set this flag in production, because on both mainnet
+    /// and testnet it would be infeasible to catch up from genesis without epoch sync.
+    #[serde(default)]
+    pub disable_epoch_sync_for_bootstrapping: bool,
+    /// If true, the node will ignore epoch sync requests from the network. It is strongly
+    /// recommended not to set this flag, because it will prevent other nodes from
+    /// bootstrapping. This flag is only included as a kill-switch and may be removed in a
+    /// future release. Please note that epoch sync requests are heavily rate limited and
+    /// cached, and therefore should not affect the performance of the node or introduce
+    /// any non-negligible increase in network traffic.
+    #[serde(default)]
+    pub ignore_epoch_sync_network_requests: bool,
+    /// This serves as two purposes: (1) the node will not epoch sync and instead resort to
+    /// header sync, if the genesis block is within this many blocks from the current block;
+    /// (2) the node will reject an epoch sync proof if the provided proof is for an epoch
+    /// that is more than this many blocks behind the current block.
     pub epoch_sync_horizon: BlockHeightDelta,
+    /// Timeout for epoch sync requests. The node will continue retrying indefinitely even
+    /// if this timeout is exceeded.
     #[serde(with = "near_time::serde_duration_as_std")]
     pub timeout_for_epoch_sync: Duration,
 }
 
 impl Default for EpochSyncConfig {
     fn default() -> Self {
         Self {
-            enabled: false,
+            disable_epoch_sync_for_bootstrapping: false,
+            ignore_epoch_sync_network_requests: false,
             // Mainnet is 43200 blocks per epoch, so let's default to epoch sync if
             // we're more than 5 epochs behind, and we accept proofs up to 2 epochs old.
             // (Epoch sync should not be picking a target epoch more than 2 epochs old.)

integration-tests/src/test_loop/tests/epoch_sync.rs

@@ -141,7 +141,6 @@ fn bootstrap_node_via_epoch_sync(setup: TestNetworkSetup, source_node: usize) ->
         .test_loop_data_dir(tempdir)
         .config_modifier(|config, _| {
             // Enable epoch sync, and make the horizon small enough to trigger it.
-            config.epoch_sync.enabled = true;
             config.epoch_sync.epoch_sync_horizon = 30;
             // Make header sync horizon small enough to trigger it.
             config.block_header_fetch_horizon = 8;