[SOLVED] Kafka access inside and outside docker

Kafka access inside and outside docker

I'm trying to start a kafka service using docker-compose, and it should be able to be accessed inside and outside docker. So, it should be matter of setting the right advertisers inside and outside:

version: '3'
services:
  zookeeper:
    image: wurstmeister/zookeeper
    ports:
      - "2181:2181"
  kafka:
    image: wurstmeister/kafka
    ports:
      - "9094:9092"
    environment:
      KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INSIDE:PLAINTEXT,OUTSIDE:PLAINTEXT
      KAFKA_LISTENERS: INSIDE://:9092,OUTSIDE://127.0.0.1:9094
      KAFKA_ADVERTISED_LISTENERS: INSIDE://:9092,OUTSIDE://127.0.0.1:9094
      KAFKA_INTER_BROKER_LISTENER_NAME: INSIDE

The problem is that when I try to connect from outside the cluster, I don't get 127.0.0.1 as the name of the node, but the internal hostname:

$ kafkacat -L -b 127.0.0.1:9094
Metadata for all topics (from broker -1: 127.0.0.1:9092/bootstrap):
 1 brokers:
  broker 1001 at 91588ea968d4:9092
 28 topics:
 ...

Isn't the purpose of KAFKA_ADVERTISED_LISTENERS and KAFKA_LISTENERS to handle that situation? I tried setting KAFKA_ADVERTISED_HOST_NAME but it's ignored (one piece of documentation says it's deprecated, other one says that it's still active), but nevertheless that doesn't seem to be the answer, since I want two different advertised hostnames for two different networks.

I guess the old question remains: how to make kafka work inside and outside docker-compose?

Solution

Your config of the listeners looks correct, the problem is with your Docker Compose:

ports:
  - "9094:9092"

You’re mapping 9094 (‘Outside’) back to 9092 (‘Inside’) and thus when you connect you’re connecting to the ‘Inside’ listener. If you remove this line of config then your listener set up should work as intended.