[Databricks][DatabricksJDBCDriver](500593) Communication link failure. Failed to connect to server.

[violar]

I am using databricks jdbc driver to run a certain app. It runs fine for a few mins to hours and then I get the error 
[Databricks][DatabricksJDBCDriver](500593) Communication link failure. Failed to connect to server. Reason: HTTP Response code: 502, Error message: Unknown. Any suggestions to resolve this issue?

Here is the stack trace

```
java.sql.SQLException: [Databricks][DatabricksJDBCDriver](500593) Communication link failure. Failed to connect to server. Reason: HTTP Response code: 502, Error message: Unknown.
at com.databricks.client.hivecommon.api.HS2Client.handleTTransportException(Unknown Source)
at com.databricks.client.spark.jdbc.DowloadableFetchClient.handleTTransportException(Unknown Source)
at com.databricks.client.hivecommon.api.HS2Client.openSession(Unknown Source)
at com.databricks.client.hivecommon.api.HS2Client.<init>(Unknown Source)
at com.databricks.client.spark.jdbc.DowloadableFetchClient.<init>(Unknown Source)
at com.databricks.client.spark.jdbc.DownloadableFetchClientFactory.createClient(Unknown Source)
at com.databricks.client.hivecommon.core.HiveJDBCCommonConnection.connectToServer(Unknown Source)
at com.databricks.client.spark.core.SparkJDBCConnection.connectToServer(Unknown Source)
at com.databricks.client.hivecommon.core.HiveJDBCCommonConnection.establishConnection(Unknown Source)
at com.databricks.client.spark.core.SparkJDBCConnection.establishConnection(Unknown Source)
at com.databricks.client.jdbc.core.LoginTimeoutConnection.connect(Unknown Source)
at com.databricks.client.jdbc.common.BaseConnectionFactory.doConnect(Unknown Source)
at com.databricks.client.jdbc.common.AbstractDriver.connect(Unknown Source)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at world.data.external.jdbc.sandbox.ContextClassLoaderProxy.invoke(ContextClassLoaderProxy.java:82)
at jdk.proxy3/jdk.proxy3.$Proxy15.connect(Unknown Source)
Caused by: com.databricks.client.support.exceptions.ErrorException: [Databricks][DatabricksJDBCDriver](500593) Communication link failure. Failed to connect to server. Reason: HTTP Response code: 502, Error message: Unknown.
... 58 common frames omitted
Caused by: com.databricks.client.jdbc42.internal.apache.thrift.transport.TTransportException: HTTP Response code: 502, Error message: Unknown
at com.databricks.client.hivecommon.api.TETHttpClient.handleHeaderErrorMessage(Unknown Source)
at com.databricks.client.hivecommon.api.TETHttpClient.handleErrorResponse(Unknown Source)
at com.databricks.client.hivecommon.api.TETHttpClient.flushUsingHttpClient(Unknown Source)
at com.databricks.client.hivecommon.api.TETHttpClient.flush(Unknown Source)
at com.databricks.client.jdbc42.internal.apache.thrift.TServiceClient.sendBase(TServiceClient.java:73)
at com.databricks.client.jdbc42.internal.apache.thrift.TServiceClient.sendBase(TServiceClient.java:62)
at com.databricks.client.jdbc42.internal.apache.hive.service.rpc.thrift.TCLIService$Client.send_OpenSession(TCLIService.java:147)
at com.databricks.client.hivecommon.api.HS2ClientWrapper.send_OpenSession(Unknown Source)
at com.databricks.client.jdbc42.internal.apache.hive.service.rpc.thrift.TCLIService$Client.OpenSession(TCLIService.java:139)
at com.databricks.client.hivecommon.api.HS2ClientWrapper.callOpenSession(Unknown Source)
at com.databricks.client.hivecommon.api.HS2ClientWrapper.access$1700(Unknown Source)
at com.databricks.client.hivecommon.api.HS2ClientWrapper$18.clientCall(Unknown Source)
at com.databricks.client.hivecommon.api.HS2ClientWrapper$18.clientCall(Unknown Source)
at com.databricks.client.hivecommon.api.HS2ClientWrapper.executeWithRetry(Unknown Source)
at com.databricks.client.hivecommon.api.HS2ClientWrapper.OpenSession(Unknown Source)
... 56 common frames omitted

```

[Kaniz_Fatma]

Hi @violar, The error you’re encountering with the Databricks JDBC driver can be quite frustrating, but let’s troubleshoot it together.

Here are a few suggestions to resolve this issue:

1. Check Your Authentication Mechanism:

   • The error message indicates a communication link failure. One common cause is incorrect authentication. Ensure that you’re using the correct authentication method.
   • In your Java code, you’re explicitly passing the username and password to DriverManager.getConnection(url, username, password). However, Databricks typically uses tokens for authentication.
   • Try connecting without specifying the username and password:

     Connection connection = DriverManager.getConnection(url);
     

   • Make sure your token is valid and hasn’t expired.

2. Verify Token and URL:

   • Double-check that the token in your URL is correct. Regenerate the token if needed.
   • Ensure that the URL is accurate and points to the correct Databricks cluster.

3. HTTP Response Code 502:

   • A 502 Bad Gateway error typically indicates an issue with the gateway server (e.g., reverse proxy or load balancer) between your client and the Databricks service.
   • Check for any network issues or if the Databricks service is experiencing problems.

4. Network and Firewall Settings:

   • Ensure that your network allows outbound connections to the Databricks service.
   • Check if any firewall rules are blocking the communication.

5. Driver Version Compatibility:

   • Verify that your Databricks JDBC driver version (com.databricks:databricks-jdbc) is compatible with your Databricks cluster version.
   • Consider updating the driver to a more recent version if needed.

6. Thread Leakage (Advanced):

   • If you suspect thread leakage, ensure you close connections and resources appropriately.
   • Review your code to see if there are any unclosed connections or resources.

Remember to test each step after making changes. Hopefully, one of these suggestions will help you resolve the issue. If you continue to face problems, consider reaching out for further assistance. Good luck! 🚀