Bad KAFKA_ADVERTISED_LISTENERS when exposing host ports to the container

This issue relates to the Kafka module.

When using the testcontainers utility to expose host ports to all containers (see https://www.testcontainers.org/features/networking/#exposing-host-ports-to-the-container), KafkaContainer faills to start Kafka due to an internal misconfiguration.

The error seen from the Kafka container logs is the following:

java.lang.IllegalArgumentException: requirement failed: Each listener must have a different port, listeners: PLAINTEXT://localhost:32889,BROKER://192.168.0.2:9092,BROKER://172.17.0.4:9092

From my analysis, it seems that, when using the feature, testcontainers adds the additional bridge network to each container which messes up with the setup of the KAFKA_ADVERTISED_LISTENERS environment variable of the KafkaContainer class (see https://github.com/testcontainers/testcontainers-java/blob/master/modules/kafka/src/main/java/org/testcontainers/containers/KafkaContainer.java#L115-L121).

We change the affected part to use different ports when multiple networks are present, but I'm not sure of the implications. Any thoughts on the subject?

Start with modules/kafka/src/main/java/org/testcontainers/containers/KafkaContainer.java around lines 115-121 and review the networking documentation for exposing host ports to containers. Reproduce the failure with an additional bridge network and check how KAFKA_ADVERTISED_LISTENERS is assembled. Done means KafkaContainer starts successfully with distinct listener ports in this configuration.