Randall Hauch created KAFKA-8368:
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Summary: Errors when attempting to use connectors that are in
multiple Kafka Connect plugins
Key: KAFKA-8368
URL: https://issues.apache.org/jira/browse/KAFKA-8368
Project: Kafka
Issue Type: Bug
Components: KafkaConnect
Affects Versions: 0.11.0.0
Reporter: Randall Hauch
This problem was introduced with the classloader isolation in
[KIP-146|https://cwiki.apache.org/confluence/display/KAFKA/KIP-146+-+Classloading+Isolation+in+Connect].
It's not normally a problem since a known limitation is that Connect does not
support multiple versions of the same connector.
However, this problem can occur even when each connector is installed only
once, when one connector plugin is based on and specializes a different
connector plugin. This can lead to an ambiguity when instantiating one of the
connectors that appears in multiple plugins.
Consider an example where plugin "foo" contains the "com.acme.FooConnector"
class, and plugin "bar" contains a "org.other.BarConnector" class that depends
on the "com.acme.FooConnector" class and therefore includes the "foo" JARs in
the "bar" plugin. In this case, the "com.acme.FooConnector" appears in two
plugins, and when a user chooses to run a connector using the
"com.acme.FooConnector" class, Connect will choose (depending upon JVM) either
the "foo" plugin or the "bar" plugin. In some cases, this might be the wrong
one (e.g., the "bar" plugin contains an older version of "foo".
Arguably this is another manifestation of the version problem, but in this case
the "bar" plugin does not intend to expose the "com.acme.FooConnector" -- and
if it does then the "foo" plugin is installed and should take precedence.
One potential solution is to hide any concrete connector class in a plugin when
that class a) is subclassed in that same plugin, and b) not subclassed in a
different plugin.
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