Sagar Rao created KAFKA-16592:
---------------------------------

             Summary: ConfigKey constructor update can break clients using it
                 Key: KAFKA-16592
                 URL: https://issues.apache.org/jira/browse/KAFKA-16592
             Project: Kafka
          Issue Type: Bug
            Reporter: Sagar Rao
            Assignee: Sagar Rao


In [KAFKA-14957|https://issues.apache.org/jira/browse/KAFKA-14957], the 
constructor of ConfigDef.ConfigKey was updated to add a new argument called 
{*}alternativeString{*}. As part of the PR, new *define* methods were also 
added which makes sense. However, since the constructor of 
*ConfigDef.ConfigKey* itself can be used directly by other clients which import 
the dependency, this can break all clients who were using the older constructor 
w/o the *alternativeString* argument. 

I bumped into this when I was testing 
the[kafka-connect-redis|[https://github.com/jcustenborder/kafka-connect-redis/tree/master]]
 connector. It starts up correctly against the official 3.7 release, but fails 
with the following error when run against a 3.8 snapshot

 

 
{code:java}
Caused by: java.lang.NoSuchMethodError: 
org.apache.kafka.common.config.ConfigDef$ConfigKey.<init>(Ljava/lang/String;Lorg/apache/kafka/common/config/ConfigDef$Type;Ljava/lang/Object;Lorg/apache/kafka/common/config/ConfigDef$Validator;Lorg/apache/kafka/common/config/ConfigDef$Importance;Ljava/lang/String;Ljava/lang/String;ILorg/apache/kafka/common/config/ConfigDef$Width;Ljava/lang/String;Ljava/util/List;Lorg/apache/kafka/common/config/ConfigDef$Recommender;Z)V
 at 
com.github.jcustenborder.kafka.connect.utils.config.ConfigKeyBuilder.build(ConfigKeyBuilder.java:62)
 at 
com.github.jcustenborder.kafka.connect.redis.RedisConnectorConfig.config(RedisConnectorConfig.java:133)
 at 
com.github.jcustenborder.kafka.connect.redis.RedisSinkConnectorConfig.config(RedisSinkConnectorConfig.java:46)
 at 
com.github.jcustenborder.kafka.connect.redis.RedisSinkConnector.config(RedisSinkConnector.java:73)
 at 
org.apache.kafka.connect.runtime.AbstractHerder.validateConnectorConfig(AbstractHerder.java:538)
 at 
org.apache.kafka.connect.runtime.AbstractHerder.lambda$validateConnectorConfig$3(AbstractHerder.java:412)
 at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
 at java.util.concurrent.FutureTask.run(FutureTask.java:266)
 at 
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
 at 
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 ... 1 more
 
{code}
 

The reason for that is that the connector uses another library called 
connect-utils which invokes the old constructor 
[directly|https://github.com/jcustenborder/connect-utils/blob/master/connect-utils/src/main/java/com/github/jcustenborder/kafka/connect/utils/config/ConfigKeyBuilder.java#L62]

It is not expected for connector invocations to fail across versions so this 
would cause confusion.

We could argue that why is the constructor being invoked directly instead of 
using the *define* method, but there might be other clients doing the same. We 
should add the old constructor back which calls the new one by setting the 
*alternativeString* to null.



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