Docker-Compose on Micha Kops' Tech Notes

Avro Schema Compatibility and the Confluent Schema Registry

Sun, 08 Jun 2025 00:00:00 +0200

What is Schema Compatibility?

Schema compatibility ensures that data serialized by a producer using one schema can be deserialized by a consumer using another. The Confluent Schema Registry provides several compatibility modes to enforce these rules when updating schemas.

There are two key directions of compatibility:

Backward Compatibility (Upward Compatibility): Old consumers can read data produced with a newer schema.
Forward Compatibility (Downward Compatibility): New consumers can read data produced with an older schema.

Postgres with docker-compose or Docker and pg_stat_statements enabled

Wed, 29 Mar 2023 00:00:00 +0200

pg_stat_statements is useful to gather performance information about queries so lets add it to our dockerized postgres database.

Using docker-compose

Using docker-compose we just need to add the following docker-compose.yaml:

docker-compose.yml

version: '3.5'

services:
  postgres:
    container_name: postgres_container
    image: postgres
    ports:
      - "5432:5432"
    volumes:
      - /var/lib/postgresql/data
    # used for query profiling, deactivate for enhanced performance
    command: postgres -c shared_preload_libraries=pg_stat_statements -c pg_stat_statements.track=all -c max_connections=200
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: thepassword

We simply start our Postgres database with docker-compose:

Setting up multiple Postgresql Instances with docker-compose

Tue, 08 Feb 2022 00:00:00 +0100

A simple setup when two Postgres databases prefilled with schema/data needed.

docker-compose.yml

version: '3.6'
services:
    postgres1:
        image: postgres
        restart: always
        environment:
            - DATABASE_HOST=127.0.0.1
            - POSTGRES_USER=root
            - POSTGRES_PASSWORD=root
            - POSTGRES_DB=root
        ports:
            - "15432:15432"
        volumes:
            - ./postgres1-init.sql:/docker-entrypoint-initdb.d/docker_postgres_init.sql

    postgres2:
        image: postgres
        restart: always
        environment:
            - DATABASE_HOST=127.0.0.1
            - POSTGRES_USER=root
            - POSTGRES_PASSWORD=root
            - POSTGRES_DB=root

        ports:
            - "25432:25432"
        volumes:
            - ./postgres2-init.sql:/docker-entrypoint-initdb.d/docker_postgres_init.sql

And our sample init scripts:

CREATE USER tester WITH PASSWORD 'tester' CREATEDB;
CREATE DATABASE testdb
    WITH
    OWNER = tester
    ENCODING = 'UTF8'
    LC_COLLATE = 'en_US.utf8'
    LC_CTYPE = 'en_US.utf8'
    TABLESPACE = pg_default
    CONNECTION LIMIT = -1;

Kafka Java Quickstart with Docker

Sat, 29 Jan 2022 00:00:00 +0100

Goals

Setup Kafka and Zookeeper with Docker and docker-compose
Create a message consumer and producer in Java

Kafka Setup

We’re using docker-compose to set up our message broker, zookeper and other stuff using confluent-platform.

This is our docker-compose.yaml config file from Confluent’s following GitHub repository.

docker-compose.yaml

---
version: '2'
services:
  zookeeper:
    image: confluentinc/cp-zookeeper:7.0.1
    hostname: zookeeper
    container_name: zookeeper
    ports:
      - "2181:2181"
    environment:
      ZOOKEEPER_CLIENT_PORT: 2181
      ZOOKEEPER_TICK_TIME: 2000

  broker:
    image: confluentinc/cp-kafka:7.0.1
    hostname: broker
    container_name: broker
    depends_on:
      - zookeeper
    ports:
      - "29092:29092"
      - "9092:9092"
      - "9101:9101"
    environment:
      KAFKA_BROKER_ID: 1
      KAFKA_ZOOKEEPER_CONNECT: 'zookeeper:2181'
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT
      KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://broker:29092,PLAINTEXT_HOST://localhost:9092
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
      KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
      KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0
      KAFKA_JMX_PORT: 9101
      KAFKA_JMX_HOSTNAME: localhost

  schema-registry:
    image: confluentinc/cp-schema-registry:7.0.1
    hostname: schema-registry
    container_name: schema-registry
    depends_on:
      - broker
    ports:
      - "8081:8081"
    environment:
      SCHEMA_REGISTRY_HOST_NAME: schema-registry
      SCHEMA_REGISTRY_KAFKASTORE_BOOTSTRAP_SERVERS: 'broker:29092'
      SCHEMA_REGISTRY_LISTENERS: http://0.0.0.0:8081

  connect:
    image: cnfldemos/kafka-connect-datagen:0.5.0-6.2.0
    hostname: connect
    container_name: connect
    depends_on:
      - broker
      - schema-registry
    ports:
      - "8083:8083"
    environment:
      CONNECT_BOOTSTRAP_SERVERS: 'broker:29092'
      CONNECT_REST_ADVERTISED_HOST_NAME: connect
      CONNECT_GROUP_ID: compose-connect-group
      CONNECT_CONFIG_STORAGE_TOPIC: docker-connect-configs
      CONNECT_CONFIG_STORAGE_REPLICATION_FACTOR: 1
      CONNECT_OFFSET_FLUSH_INTERVAL_MS: 10000
      CONNECT_OFFSET_STORAGE_TOPIC: docker-connect-offsets
      CONNECT_OFFSET_STORAGE_REPLICATION_FACTOR: 1
      CONNECT_STATUS_STORAGE_TOPIC: docker-connect-status
      CONNECT_STATUS_STORAGE_REPLICATION_FACTOR: 1
      CONNECT_KEY_CONVERTER: org.apache.kafka.connect.storage.StringConverter
      CONNECT_VALUE_CONVERTER: io.confluent.connect.avro.AvroConverter
      CONNECT_VALUE_CONVERTER_SCHEMA_REGISTRY_URL: http://schema-registry:8081
      CONNECT_PLUGIN_PATH: "/usr/share/java,/usr/share/confluent-hub-components"
      CONNECT_LOG4J_LOGGERS: org.apache.zookeeper=ERROR,org.I0Itec.zkclient=ERROR,org.reflections=ERROR

  ksqldb-server:
    image: confluentinc/cp-ksqldb-server:7.0.1
    hostname: ksqldb-server
    container_name: ksqldb-server
    depends_on:
      - broker
      - connect
    ports:
      - "8088:8088"
    environment:
      KSQL_CONFIG_DIR: "/etc/ksql"
      KSQL_BOOTSTRAP_SERVERS: "broker:29092"
      KSQL_HOST_NAME: ksqldb-server
      KSQL_LISTENERS: "http://0.0.0.0:8088"
      KSQL_CACHE_MAX_BYTES_BUFFERING: 0
      KSQL_KSQL_SCHEMA_REGISTRY_URL: "http://schema-registry:8081"
      KSQL_PRODUCER_INTERCEPTOR_CLASSES: "io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor"
      KSQL_CONSUMER_INTERCEPTOR_CLASSES: "io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor"
      KSQL_KSQL_CONNECT_URL: "http://connect:8083"
      KSQL_KSQL_LOGGING_PROCESSING_TOPIC_REPLICATION_FACTOR: 1
      KSQL_KSQL_LOGGING_PROCESSING_TOPIC_AUTO_CREATE: 'true'
      KSQL_KSQL_LOGGING_PROCESSING_STREAM_AUTO_CREATE: 'true'

  ksqldb-cli:
    image: confluentinc/cp-ksqldb-cli:7.0.1
    container_name: ksqldb-cli
    depends_on:
      - broker
      - connect
      - ksqldb-server
    entrypoint: /bin/sh
    tty: true

  ksql-datagen:
    image: confluentinc/ksqldb-examples:7.0.1
    hostname: ksql-datagen
    container_name: ksql-datagen
    depends_on:
      - ksqldb-server
      - broker
      - schema-registry
      - connect
    command: "bash -c 'echo Waiting for Kafka to be ready... && \
                       cub kafka-ready -b broker:29092 1 40 && \
                       echo Waiting for Confluent Schema Registry to be ready... && \
                       cub sr-ready schema-registry 8081 40 && \
                       echo Waiting a few seconds for topic creation to finish... && \
                       sleep 11 && \
                       tail -f /dev/null'"
    environment:
      KSQL_CONFIG_DIR: "/etc/ksql"
      STREAMS_BOOTSTRAP_SERVERS: broker:29092
      STREAMS_SCHEMA_REGISTRY_HOST: schema-registry
      STREAMS_SCHEMA_REGISTRY_PORT: 8081

  rest-proxy:
    image: confluentinc/cp-kafka-rest:7.0.1
    depends_on:
      - broker
      - schema-registry
    ports:
      - 8082:8082
    hostname: rest-proxy
    container_name: rest-proxy
    environment:
      KAFKA_REST_HOST_NAME: rest-proxy
      KAFKA_REST_BOOTSTRAP_SERVERS: 'broker:29092'
      KAFKA_REST_LISTENERS: "http://0.0.0.0:8082"
      KAFKA_REST_SCHEMA_REGISTRY_URL: 'http://schema-registry:8081'

MySQL and phpMyAdmin Setup with Docker-Compose

Fri, 14 May 2021 00:00:00 +0200

Goals

Setup mySQL with phpMyAdmin connected using docker-compose (for development purpose)

Prerequisites

docker-compose installed

Setup

This is our docker-compose.yml:

version: '3.2'

services:
   db:
      image: mysql:8.0
      container_name: mysql-container
      restart: always
      ports:
       - '6603:3306'
      environment:
        MYSQL_ROOT_PASSWORD: 12345678

   app:
      depends_on:
       - db
      image: phpmyadmin/phpmyadmin
      container_name: phpmyadmin
      restart: always
      ports:
       - '8080:80'
      environment:
        PMA_HOST: db

Running

docker-compose up
Starting mysql-container ... done
Starting phpmyadmin      ... done
Attaching to mysql-container, phpmyadmin
[..]

We may now login using the following ultra-secure credentials ;) User: root, Password: 12345678

WordPress Docker Setup

Fri, 14 May 2021 00:00:00 +0200

Goals

Run WordPress via Docker / Docker-Compose
Increase the Upload Filesize Limit

Create Docker Compose Configuration

Create a docker-compose.yml:

version: '3.1'

services:

  wordpress:
    image: wordpress
    restart: always
    ports:
      - 8080:80
    environment:
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_USER: exampleuser
      WORDPRESS_DB_PASSWORD: examplepass
      WORDPRESS_DB_NAME: exampledb
    volumes:
      - wordpress:/var/www/html

  db:
    image: mysql:5.7
    restart: always
    environment:
      MYSQL_DATABASE: exampledb
      MYSQL_USER: exampleuser
      MYSQL_PASSWORD: examplepass
      MYSQL_RANDOM_ROOT_PASSWORD: '1'
    volumes:
      - db:/var/lib/mysql

volumes:
  wordpress:
  db:

Run Docker Compose / Start Containers

docker-compose up
WARNING: Found orphan containers (wordpress-docker_phpmyadmin_1) for this project. If you removed or renamed this service in your compose file, you can run this command with the --remove-orphans flag to clean it up.
Starting wordpress-docker_db_1        ... done
Starting wordpress-docker_wordpress_1 ... done
Attaching to wordpress-docker_db_1, wordpress-docker_wordpress_1
[..]
db_1         | 2021-04-03T18:58:17.247963Z 0 [Note] mysqld: ready for connections.
db_1         | Version: '5.7.33'  socket: '/var/run/mysqld/mysqld.sock'  port: 3306  MySQL Community Server (GPL)

Docker Snippets

Mon, 01 Mar 2010 00:00:00 +0100

Restrict Network

Can be useful when using a third-party image that we do not trust

Run with no network

docker run --network none <image>

Run with private isolated network

At least containers attached to this network can talk with another

docker network create --internal my_isolated_network
docker run --network my_isolated_network <image>

Block using firewall

e.g. using iptables or ipfw

# Get container's IP
docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' <container_name>

# Block all outbound connections from that IP
sudo iptables -I DOCKER-USER -s <container_ip> -j DROP