Multiple processes in one container (like Kafka+Zookeeper)
Often, I need an instance of Kafka for development purpose - if you develop services in a microservice architecture you know my problem! - but the latest versions of Kafka need an instance of Zookeeper to start. It’s very frustrating that you need a docker-compose only to make a test!
In most cases you don’t need a cluster to test your work but only a single broker, so I have created a docker image containing Zookeeper and Kafka (version 2.12-2.3.0) together, the container starts one instance of supervisor http://supervisord.org/ that manage the processes life. I’ll show you how to do step by step:
Download a stable version of Kafka from https://kafka.apache.org/, then:
FROM adoptopenjdk/openjdk11-openj9
LABEL maintainer="pasquale.paola@gmail.com"
COPY start.sh /
RUN apt update && apt install -y supervisor && chmod a+x /start.sh
ADD kafka_2.12-2.3.0 kafka_2.12-2.3.0
COPY supervisord.conf /etc/supervisor/conf.d/supervisord.conf
EXPOSE 2181 9092
CMD ["/start.sh"]
- In the first line I want to use adoptopenjdk as base image because it is debian based (I want to use apt) and it has a valid openjdk already installed
- COPY the start.sh file in the root (details below)
- An apt update it’s needed to synchronize the package manager repositories
- Then install supervisor and add a copy of Kafka as is and copy the following supervisor.conf file
The start.sh manages the environment variable KAFKA_ADVERTISED_LISTNERS used to configure the Kafka advertise url.
#!/bin/bash -e
if [[ -z "$KAFKA_ADVERTISED_LISTNERS" ]]; then
echo "ERROR: missing mandatory config: KAFKA_ADVERTISED_LISTNERS"
exit 1
fi
echo "advertised.listeners=PLAINTEXT://$KAFKA_ADVERTISED_LISTNERS:9092" >> /kafka_2.12-2.3.0/config/server.properties
exec "/usr/bin/supervisord" "-c" "/etc/supervisor/conf.d/supervisord.conf"
At the end of start.sh, it starts the supervisor daemon with the following configuration:
[supervisord]
nodaemon=true
[program:zookeeper]
directory=/
user=root
command=/kafka_2.12-2.3.0/bin/zookeeper-server-start.sh /kafka_2.12-2.3.0/config/zookeeper.properties
stdout_logfile=/dev/fd/1
stdout_logfile_maxbytes=0
redirect_stderr=true
[program:kafka]
directory=/
user=root
command=/kafka_2.12-2.3.0/bin/kafka-server-start.sh /kafka_2.12-2.3.0/config/server.properties
stdout_logfile=/dev/fd/1
stdout_logfile_maxbytes=0
redirect_stderr=true
starters=5
Supervisor starts Zookeeper and one Kafka broker: that’s all. The container is now running with a valid instance of Zookeeper and Kafka, you can bind the standard ports to interact with Kafka and Zookeeper.
Build
docker build -t paspaola/kafka-one-container .
Run
docker run -it -p2181:2181 -p9092:9092 -e "KAFKA_ADVERTISED_LISTNERS={your-host-address}" paspaola/kafka-one-container