Kafka Binder does not work with multiple bindings

[sadanyoyo]

I use this version of the package: org.springframework.cloud:spring-cloud-stream-binder-kafka:4.3.1, when using the Kafka Binder to consume messages from two different Kafka Cluster the app start fails.

I have a similar application.yml file like the following:

spring:
  application:
    name: xxx
  cloud:
    stream:
      default-binder: outbox
      binders:
        outbox:
          type: kafka
          environment:
            spring:
              kafka:
                bootstrap-servers: broker-0:9092,broker-1:9092,broker-2:9092
                consumer:
                  ack.mode: MANUAL
                  allow.auto.create.topics: false
        eventbus:
          type: kafka
          environment:
            spring:
              kafka:
                bootstrap-servers:eventbus-broker-0:9092,eventbus-broker-1:9092,eventbus-broker-2:9092
        default:
          consumer:
            ack-mode: MANUAL

Localhost is used every time when the connection is established, and the bootstrap-servers configuration does not seem to take effect. It seems that the KafkaBinderConfigurationProperties.mergedProducerConfiguration method overwrites the ProducerConfig.BOOTSTRAP_SERVERS_CONFIG configuration with the kafkaConnectionDetails configuration every time. Since I did not define spring.kafka properties, the default value localhost was used during the KafkaProperties class initialization.