Q:

KAFKA and SSL : java.lang.OutOfMemoryError: Java heap space when using kafka-topics command on KAFKA SSL cluster

this is my first post on Stackoverflow, i hope i didnt choose the wrong section.
Context : 
Kafka HEAP size is configured on following file :
/etc/systemd/system/kafka.service

With following parameter : 
Environment="KAFKA_HEAP_OPTS=-Xms6g -Xmx6g"

OS is "CentOS Linux release 7.7.1908".
Kafka is "confluent-kafka-2.12-5.3.1-1.noarch", installed from the following repository :
# Confluent REPO
[Confluent.dist]
name=Confluent repository (dist)
baseurl=http://packages.confluent.io/rpm/5.3/7
gpgcheck=1
gpgkey=http://packages.confluent.io/rpm/5.3/archive.key
enabled=1

[Confluent]
name=Confluent repository
baseurl=http://packages.confluent.io/rpm/5.3
gpgcheck=1
gpgkey=http://packages.confluent.io/rpm/5.3/archive.key
enabled=1

I activated SSL on a 3-machine KAFKA cluster few days ago, and suddently, the following command stopped working :
kafka-topics --bootstrap-server <the.fqdn.of.server>:9093 --describe --topic <TOPIC-NAME>

Which return me the following error :
[2019-10-03 11:38:52,790] ERROR Uncaught exception in thread 'kafka-admin-client-thread | adminclient-1':(org.apache.kafka.common.utils.KafkaThread) 
java.lang.OutOfMemoryError: Java heap space
    at java.nio.HeapByteBuffer.<init>(HeapByteBuffer.java:57)
    at java.nio.ByteBuffer.allocate(ByteBuffer.java:335)
    at org.apache.kafka.common.memory.MemoryPool$1.tryAllocate(MemoryPool.java:30)
    at org.apache.kafka.common.network.NetworkReceive.readFrom(NetworkReceive.java:112)
    at org.apache.kafka.common.network.KafkaChannel.receive(KafkaChannel.java:424)
    at org.apache.kafka.common.network.KafkaChannel.read(KafkaChannel.java:385)
    at org.apache.kafka.common.network.Selector.attemptRead(Selector.java:651)
    at org.apache.kafka.common.network.Selector.pollSelectionKeys(Selector.java:572)
    at org.apache.kafka.common.network.Selector.poll(Selector.java:483)
    at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:539)
    at org.apache.kafka.clients.admin.KafkaAdminClient$AdminClientRunnable.run(KafkaAdminClient.java:1152)
    at java.lang.Thread.run(Thread.java:748)

On the server's log, the following line appears when i try to request it via "kafka-topics" :
/var/log/kafka/server.log :
[2019-10-03 11:41:11,913] INFO [SocketServer brokerId=<ID>] Failed authentication with /<ip.of.the.server> (SSL handshake failed) (org.apache.kafka.common.network.Selector)

I was able to use this command properly BEFORE implementing SSL on the cluster. Here is the configuration i'm using.
All functionnality work properly (consumers, producers...) except "kafka-topics" :
# SSL Configuration
ssl.truststore.location=<truststore-path>
ssl.truststore.password=<truststore-password>
ssl.keystore.type=<keystore-type>
ssl.keystore.location=<keystore-path>
ssl.keystore.password=<keystore-password>

# Enable SSL between brokers
security.inter.broker.protocol=SSL

# Listeners
listeners=SSL://<fqdn.of.the.server>:9093
advertised.listeners=SSL://<fqdn.of.the.server>:9093

There is no problem with the certificate (which is signed by internal CA, internal CA which i added to the truststore specified on the configuration). OpenSSL show no errors : 
openssl s_client -connect <fqdn.of.the.server>:9093 -tls1
>> Verify return code: 0 (ok)

The following command is working pretty well with SSL, thanks to parameter "-consumer.config client-ssl.properties"
kafka-console-consumer --bootstrap-server <fqdn.of.the.server>:9093 --topic <TOPIC-NAME> -consumer.config client-ssl.properties

"client-ssl.properties" content is :
security.protocol=SSL
ssl.truststore.location=<truststore-path>
ssl.truststore.password=<truststore-password>

Right now, i'm forced to use "--zookeeper", which according to the documentation, is deprecated :
--zookeeper <String: hosts>              DEPRECATED, The connection string for  
                                       the zookeeper connection in the form 
                                       host:port. Multiple hosts can be     
                                       given to allow fail-over. 

And of course, it's working pretty well :
kafka-topics --zookeeper <fqdn.of.the.server>:2181 --describe --topic <TOPIC-NAME>
Topic:<TOPIC-NAME>  PartitionCount:3    ReplicationFactor:2 
Configs:
Topic: <TOPIC-NAME> Partition: 0    Leader: <ID-3>      Replicas: <ID-3>,<ID-1> Tsr: <ID-1>,<ID-3>
Topic: <TOPIC-NAME> Partition: 1    Leader: <ID-1>      Replicas: <ID-1>,<ID-2> Isr: <ID-2>,<ID-1>
Topic: <TOPIC-NAME> Partition: 2    Leader: <ID-2>      Replicas: <ID-2>,<ID-3> Isr: <ID-2>,<ID-3>

So, my question is : why am i unable to use "--bootstrap-server" atm ? Because of the "zookeeper" deprecation, i'm worried about not to be able to consult my topics, and their details...
I believe that kafka-topics needs the same option than kafka-console-consumer, aka "-consumer.config"...
Ask if any additionnal precision needed.
Thanks a lot, hope my question is clear and readable.
Blyyyn

A:

I finally found a way to deal with this SSL error. The key is to use the following setting :
--command-config client-ssl.properties

This is working with the most part of KAFKA commands, like kafka-consumer-groups, and of course kafka-topics. See examples below :
kafka-consumer-groups --bootstrap-server <kafka-hostname>:<kafka-port> --group <consumer-group> --topic <topic> --reset-offsets --to-offset <offset> --execute --command-config <ssl-config>

kafka-topics --list --bootstrap-server <kafka-hostname>:<kafka-port> --command-config client-ssl.properties

ssl-config was "client-ssl.properties",see initial post for content.
Beware, by using IP address on , you'll have an error if the machine certificate doesnt have alternative name with that IP address. Try to have correct DNS resolution and use FQDN if possible.
Hope this solution will help, cheers!
Blyyyn

