Other BookNest containers reach Kafka 129 on the shared network as l3-kafka:9092; host programs use localhost:33092. A few habits keep the workstation stack manageable:
One named network, so later Compose projects (Connect, a schema registry, a UI) join without edits.
Bounded heaps (KAFKA_HEAP_OPTS, 1 GB by default): Kafka's speed comes from the page cache, not the heap.
One heavy service at a time on four cores: stop the six-node cluster before Spark 129 or Airflow 129 runs.