Fix channel open trace logging (#81308)

Today we log `Tcp transport channel opened` when the channel is created,
before it is connected, which means its addresses are not configured so
it appears as `Netty4TcpChannel{localAddress=null, remoteAddress=null}`
which is pretty useless. This commit defers the logging until the
channel is actually open at which point its addresses are available.

server/src/main/java/org/elasticsearch/transport/TcpTransport.java

@@ -352,8 +352,10 @@ public abstract class TcpTransport extends AbstractLifecycleComponent implements
 
         for (int i = 0; i < numConnections; ++i) {
             try {
-                TcpChannel channel = initiateChannel(node);
-                logger.trace(() -> new ParameterizedMessage("Tcp transport channel opened: {}", channel));
+                final TcpChannel channel = initiateChannel(node);
+                if (logger.isTraceEnabled()) {
+                    channel.addConnectListener(new ChannelOpenTraceLogger(channel));
+                }
                 channels.add(channel);
             } catch (ConnectTransportException e) {
                 CloseableChannel.closeChannels(channels, false);
@@ -1112,4 +1114,25 @@ public abstract class TcpTransport extends AbstractLifecycleComponent implements
         }
     }
 
+    private static final class ChannelOpenTraceLogger implements ActionListener<Void> {
+        private final TcpChannel channel;
+
+        ChannelOpenTraceLogger(TcpChannel channel) {
+            this.channel = channel;
+        }
+
+        @Override
+        public void onResponse(Void unused) {
+            logger.trace("Tcp transport channel opened: {}", channel);
+        }
+
+        @Override
+        public void onFailure(Exception e) {
+            // Connection failures are generally logged elsewhere, but go via the ChannelsConnectedListener which only captures the first
+            // exception for each bundle of channels. If the ChannelOpenTraceLogger is installed then trace-logging is enabled so we can log
+            // every failure.
+            logger.trace(new ParameterizedMessage("failed to open transport channel: {}", channel), e);
+        }
+    }
+
 }