feat: add support for debug logging (#1935)

Author: ttosta-google

README.md

@@ -39,6 +39,16 @@ mysql-socket-factory-connector-j-8–1.8.0-jar-with-dependencies.jar
 postgres-socket-factory-1.8.0-jar-with-dependencies.jar
 ```
 
+### 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
+```
+
 ---
 
 ### Firewall configuration

core/src/main/java/com/google/cloud/sql/core/Connector.java

@@ -110,18 +110,28 @@ Socket connect(ConnectionConfig config, long timeoutMs) throws IOException {
     DefaultConnectionInfoCache instance = getConnection(config);
     try {
 
-      SSLSocket socket = instance.createSslSocket(timeoutMs);
+      String instanceIp = instance.getConnectionMetadata(timeoutMs).getPreferredIpAddress();
+      logger.debug(String.format("[%s] Connecting to instance.", instanceIp));
 
+      SSLSocket socket = instance.createSslSocket(timeoutMs);
       socket.setKeepAlive(true);
       socket.setTcpNoDelay(true);
+      socket.connect(new InetSocketAddress(instanceIp, serverProxyPort));
 
-      String instanceIp = instance.getConnectionMetadata(timeoutMs).getPreferredIpAddress();
+      try {
+        socket.startHandshake();
+      } catch (IOException e) {
+        logger.debug("TLS handshake failed!");
+        throw e;
+      }
 
-      socket.connect(new InetSocketAddress(instanceIp, serverProxyPort));
-      socket.startHandshake();
+      logger.debug(String.format("[%s] Connected to instance successfully.", instanceIp));
 
       return socket;
     } catch (IOException e) {
+      logger.debug(
+          String.format(
+              "[%s] Socket connection failed! Trigger a refresh.", config.getCloudSqlInstance()));
       instance.forceRefresh();
       throw e;
     }
@@ -142,11 +152,14 @@ DefaultConnectionInfoCache getConnection(ConnectionConfig config) {
   }
 
   private DefaultConnectionInfoCache createConnectionInfo(ConnectionConfig config) {
+    logger.debug(
+        String.format("[%s] Connection info added to cache.", config.getCloudSqlInstance()));
     return new DefaultConnectionInfoCache(
         config, adminApi, instanceCredentialFactory, executor, localKeyPair, minRefreshDelayMs);
   }
 
   public void close() {
+    logger.debug("Close all connections and remove them from cache.");
     this.instances.forEach((key, c) -> c.close());
     this.instances.clear();
   }

core/src/main/java/com/google/cloud/sql/core/Refresher.java

@@ -182,6 +182,10 @@ 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(
@@ -268,11 +272,11 @@ 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);