Source: Kafka on Rails: Using Kafka with Ruby on Rails — Part 2 — Getting started with Rails and Kafka

Before we combine Kafka with Ruby, it would be good to have a workable local Kafka process. The easiest way to do that is by using our docker-compose.yml present in Karafka:

git clone git@github.com:karafka/karafka.git
cd karafka
docker-compose up

To check that it works, you can just telnet to it:

telnet 127.0.0.1 9092
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.

The docker-compose.yml we provide with Karafka has a setting called KAFKA_ADVERTISED_HOST_NAME, and it is by default set to localhost.

Modify the KAFKA_ADVERTISED_HOST_NAME to match your docker host IP if you want to connect to Kafka from other docker containers:

# KAFKA_ADVERTISED_HOST_NAME: localhost
KAFKA_ADVERTISED_HOST_NAME: 192.168.0.5

Once you've changed that, you should be able to connect from other docker containers to your Kafka by using the host IP address:

# Run an example docker container to check it via telnet
docker run -it --rm --entrypoint=bash python:3.8-slim-buster

# And then from within
apt update && apt install telnet

telnet 192.168.0.5 9092
Trying 192.168.0.5...
Connected to 192.168.0.5.
Escape character is '^]'.