Strimzi kafka connect cannot find my custom transformer but finds connector

Question

I am running a Strimzi KafkaConnect cluster which loads a custom transformer to apply a SMT to our messages. The .jar is within the image and loaded by Strimzi KafkaConnect cluster (appears in logs):

Dockerfile line:

FROM quay.io/strimzi/kafka:0.29.0-kafka-3.0.1
USER root:root
RUN mkdir -p /opt/kafka/plugins
COPY --from=unpacker /unpack/kafka-connect-aws-s3 /opt/kafka/plugins #this is the lenses.io connector and works fine
COPY ./<FILE>.jar /opt/kafka/plugins #<FILE>.jar is downloaded locally by pipeline.
USER 1001

(I have a connector also within the /opt/kafka/plugins directory and that is picked up by KafkaConnect fine)

The error I see is:

Message:               PUT /connectors/<NAME>/config returned 400 (Bad Request): Connector configuration is invalid and contains the following 2 error(s):
Invalid value <CLASS> for configuration transforms.<NAME>.type: Class <CLASS> could not be found.
Invalid value null for configuration transforms.<NAME>.type: Not a Transformation

However when I check within the image itself the file is there and the class appears to be there:

unzip -l /opt/kafka/plugins/<FILE>.jar | grep <CLASS>
     1333  07-31-2023 09:49   <CLASS>$Companion.class
     7990  07-31-2023 09:49   <CLASS>.class

Strimzi KafkaConnect logs:

k logs kafka-topics-backup-aws-connect-9f564bdcb-5qnp6 | grep <FILE>.jar
2023-08-30 13:51:49,301 INFO Loading plugin from: /opt/kafka/plugins/<FILE>.jar (org.apache.kafka.connect.runtime.isolation.DelegatingClassLoader) [main]
2023-08-30 13:51:49,973 INFO Registered loader: PluginClassLoader{pluginLocation=file:/opt/kafka/plugins/<FILE>.jar} (org.apache.kafka.connect.runtime.isolation.DelegatingClassLoader) [main]

The relevant parts of YAML for the KafkaConnectors:

spec:
  class: io.lenses.streamreactor.connect.aws.s3.sink.S3SinkConnector
  tasksMax: 1 
  config:
    topics: "<NAME>"
    connect.s3.kcql: <KCQL_STRING>
    connect.s3.padding.strategy: LeftPad
    connect.s3.padding.length: 8
    connect.s3.vhost.bucket: true
    transforms: "<NAME>"
    transforms.<NAME>.type: "<CLASS>"

I was expecting that when I create KafkaConnectors using the above transform that they would load the class and work.

Answer 1

The issue I had was that I was using Strimzi 0.29.0 (with Kafka 3.0.1) and the Transformer was being built in Java17. Once I changed the Transformer to Java11 it was located by KafkaConnect and used