It seems clients can't use a dns alias in front of a secured Kafka cluster.
So applications can only specify a list of hosts or IPs in bootstrap.servers instead of an alias encompassing all cluster nodes.
Using an alias in bootstrap.servers results in the following error :
javax.security.sasl.SaslException: An error: (java.security.PrivilegedActionException: javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: No valid credentials provided (Mechanism level: Fail to create credential. (63) - No service creds)]) occurred when evaluating SASL token received from the Kafka Broker. Kafka Client will go to AUTH_FAILED state. [Caused by javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: No valid credentials provided (Mechanism level: Fail to create credential. (63) - No service creds)]]
When using SASL/Kerberos authentication, the kafka server principal is of the form kafka@kafka/broker1.hostname.com@EXAMPLE.COM
Kerberos requires that the hosts can be resolved by their FQDNs.
During SASL handshake, the client will create a SASL token and then send it to kafka for auth.
But to create a SASL token the client first needs to be able to validate that the broker's kerberos is a valid one.
There are 3 potential options :
1. Creating a single kerberos principal not linked to a host but to an alias and reference it in the broker jaas file.
But I think the kerberos infrastructure would refuse to validate it, so the SASL handshake would still fail
2. Modify the client bootstrap mechanism to detect whether bootstrap.servers contains a dns alias. If it does, resolve and expand the alias to retrieve all hostnames behind it and add them to the list of nodes.
This could be done by modifying parseAndValidateAddresses() in ClientUtils
3. Add a cluster.alias parameter that would be handled by the logic above. Having another parameter to avoid confusion on how bootstrap.servers works behind the scene.
I would be happy to contribute the change for any of the options.
I believe the ability to use a dns alias instead of static lists of brokers would bring good deployment flexibility.