Testnet stability (#451)

* Change reduced tree for adding weightless node

* Add more comments for reduced tree fork choice

* Small refactor on reduced tree for readability

* Move test_harness forking logic into itself

* Add new `AncestorIter` trait to store

* Add unfinished tests to fork choice

* Make `beacon_state.genesis_block_root` public

* Add failing lmd_ghost fork choice tests

* Extend fork_choice tests, create failing test

* Implement Debug for generic ReducedTree

* Add lazy_static to fork choice tests

* Add verify_integrity fn to reduced tree

* Fix bugs in reduced tree

* Ensure all reduced tree tests verify integrity

* Slightly alter reduce tree test params

* Add (failing) reduced tree test

* Fix bug in fork choice

Iter ancestors was not working well with skip slots

* Put maximum depth for common ancestor search

Ensures that we don't search back past the finalized root.

* Add basic finalization tests for reduced tree

* Change fork choice to use beacon_block_root

Previously it was using target_root, which was wrong

* Change reduced tree for adding weightless node

* Add more comments for reduced tree fork choice

* Small refactor on reduced tree for readability

* Move test_harness forking logic into itself

* Add new `AncestorIter` trait to store

* Add unfinished tests to fork choice

* Make `beacon_state.genesis_block_root` public

* Add failing lmd_ghost fork choice tests

* Extend fork_choice tests, create failing test

* Implement Debug for generic ReducedTree

* Add lazy_static to fork choice tests

* Add verify_integrity fn to reduced tree

* Fix bugs in reduced tree

* Ensure all reduced tree tests verify integrity

* Slightly alter reduce tree test params

* Add (failing) reduced tree test

* Fix bug in fork choice

Iter ancestors was not working well with skip slots

* Put maximum depth for common ancestor search

Ensures that we don't search back past the finalized root.

* Add basic finalization tests for reduced tree

* Add network dir CLI flag

* Simplify "NewSlot" log message

* Rename network-dir CLI flag

* Change fork choice to use beacon_block_root

Previously it was using target_root, which was wrong

* Update db dir size for metrics

* Change slog to use `FullFormat` logging

* Update some comments and log formatting

* Add prom gauge for best block root

* Only add known target blocks to fork choice

* Add finalized and justified root prom metrics

* Add CLI flag for setting log level

* Add logger to beacon chain

* Add debug-level CLI flag to validator

* Allow block processing if fork choice fails

* Create warn log when there's low libp2p peer count

* Minor change to logging

* Make ancestor iter return option

* Disable fork choice test when !debug_assertions

* Fix type, removed code fragment

* Tidy some borrow-checker evading

* Lower reduced tree random test iterations

beacon_node/client/src/notifier.rs

@@ -2,7 +2,7 @@ use crate::Client;
 use beacon_chain::BeaconChainTypes;
 use exit_future::Exit;
 use futures::{Future, Stream};
-use slog::{debug, o};
+use slog::{debug, o, warn};
 use std::time::{Duration, Instant};
 use tokio::runtime::TaskExecutor;
 use tokio::timer::Interval;
@@ -10,6 +10,9 @@ use tokio::timer::Interval;
 /// The interval between heartbeat events.
 pub const HEARTBEAT_INTERVAL_SECONDS: u64 = 15;
 
+/// Create a warning log whenever the peer count is at or below this value.
+pub const WARN_PEER_COUNT: usize = 1;
+
 /// Spawns a thread that can be used to run code periodically, on `HEARTBEAT_INTERVAL_SECONDS`
 /// durations.
 ///
@@ -30,9 +33,16 @@ pub fn run<T: BeaconChainTypes + Send + Sync + 'static>(
     let libp2p = client.network.libp2p_service();
 
     let heartbeat = move |_| {
-        // Notify the number of connected nodes
-        // Panic if libp2p is poisoned
-        debug!(log, ""; "Connected Peers" => libp2p.lock().swarm.connected_peers());
+        // Number of libp2p (not discv5) peers connected.
+        //
+        // Panics if libp2p is poisoned.
+        let connected_peer_count = libp2p.lock().swarm.connected_peers();
+
+        debug!(log, "libp2p"; "peer_count" => connected_peer_count);
+
+        if connected_peer_count <= WARN_PEER_COUNT {
+            warn!(log, "Low libp2p peer count"; "peer_count" => connected_peer_count);
+        }
 
         Ok(())
     };