feat: add support for debug logging (#501)

README.md

@@ -54,6 +54,16 @@ for more information.
 [set-adc]: https://cloud.google.com/docs/authentication/provide-credentials-adc
 [iam-docs]: https://cloud.google.com/alloydb/docs/reference/iam-roles-permissions#roles
 
+### Debug Logging
+
+The Java Connector supports optional debug logging to help diagnose problems with
+the background certificate refresh. To enable it, add the following to the file
+`/src/main/resources/application.yml`:
+
+```
+logging.level.root=DEBUG
+```
+
 ## Support policy
 
 ### Major version lifecycle

alloydb-jdbc-connector/src/main/java/com/google/cloud/alloydb/ConnectionSocket.java

@@ -115,6 +115,8 @@ Socket connect() throws IOException {
       serverName = connectionInfo.getIpAddress();
     }
 
+    logger.debug(String.format("[%s] Connecting to instance.", address));
+
     SSLParameters sslParameters = socket.getSSLParameters();
     // Set HTTPS as the the endpoint identification algorithm
     // in order to verify the identity of the certificate as
@@ -126,12 +128,20 @@ Socket connect() throws IOException {
     socket.setKeepAlive(true);
     socket.setTcpNoDelay(true);
     socket.connect(new InetSocketAddress(address, SERVER_SIDE_PROXY_PORT));
-    socket.startHandshake();
+
+    try {
+      socket.startHandshake();
+    } catch (IOException e) {
+      logger.debug("TLS handshake failed!");
+      throw e;
+    }
 
     // The metadata exchange must occur after the TLS connection is established
     // to avoid leaking sensitive information.
     metadataExchange(socket);
 
+    logger.debug(String.format("[%s] Connected to instance successfully.", address));
+
     return socket;
   }
 

alloydb-jdbc-connector/src/main/java/com/google/cloud/alloydb/Connector.java

@@ -21,9 +21,12 @@
 import java.net.Socket;
 import java.security.KeyPair;
 import java.util.concurrent.ConcurrentHashMap;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 class Connector {
 
+  private static final Logger logger = LoggerFactory.getLogger(Connector.class);
   private static final long MIN_RATE_LIMIT_MS = 30000;
 
   private final ListeningScheduledExecutorService executor;
@@ -56,6 +59,7 @@ public ConnectorConfig getConfig() {
   }
 
   public void close() {
+    logger.debug("Close all connections and remove them from cache.");
     this.instances.forEach((key, c) -> c.close());
     this.instances.clear();
   }
@@ -69,6 +73,9 @@ Socket connect(ConnectionConfig config) throws IOException {
           new ConnectionSocket(connectionInfo, config, clientConnectorKeyPair, accessTokenSupplier);
       return socket.connect();
     } catch (IOException e) {
+      logger.debug(
+          String.format(
+              "[%s] Socket connection failed! Trigger a refresh.", config.getInstanceName()));
       connectionInfoCache.forceRefresh();
       // The Socket methods above will throw an IOException or a SocketException (subclass of
       // IOException). Catch that exception, trigger a refresh, and then throw it again so
@@ -93,6 +100,7 @@ ConnectionInfoCache getConnection(ConnectionConfig config) {
   }
 
   private ConnectionInfoCache createConnectionInfo(ConnectionConfig config) {
+    logger.debug(String.format("[%s] Connection info added to cache.", config.getInstanceName()));
     return connectionInfoCacheFactory.create(
         this.executor,
         this.connectionInfoRepo,

alloydb-jdbc-connector/src/main/java/com/google/cloud/alloydb/Refresher.java

@@ -177,6 +177,10 @@ void forceRefresh() {
   /** Force a new refresh of the instance data if the client certificate has expired. */
   void refreshIfExpired() {
     ConnectionInfo info = getConnectionInfo(DEFAULT_CONNECT_TIMEOUT_MS);
+    logger.debug(
+        String.format(
+            "[%s] Now = %s, Current client certificate expiration = %s",
+            name, Instant.now().toString(), info.getExpiration()));
     if (Instant.now().isAfter(info.getExpiration())) {
       logger.debug(
           String.format(
@@ -261,11 +265,11 @@ private ListenableFuture<ConnectionInfo> handleRefreshResult(
       // No refresh retry when the TerminalException is raised.
       final Throwable cause = e.getCause();
       if (cause instanceof TerminalException) {
-        logger.info(String.format("[%s] Refresh Operation: Failed! No retry.", name), e);
+        logger.debug(String.format("[%s] Refresh Operation: Failed! No retry.", name), e);
         throw (TerminalException) cause;
       }
 
-      logger.info(
+      logger.debug(
           String.format(
               "[%s] Refresh Operation: Failed! Starting next refresh operation immediately.", name),
           e);