This Docker images provides the confluentinc/cp-schema-registry image as base with the mDNS/ZeroConf stack on top. So you can enjoy the app while it is accessible by default as schema-registry.local. (Port 80)

• Requirements
• Getting starting
• docker-compose usage example
• Host configs
• Configure a different mDNS hostname
• Other top level domains
• Further reading

Requirements

• Host enabled Avahi daemon
• Host enabled mDNS NSS lookup

Getting starting

To get a Schema Registry service up and running create a docker-compose.yml and insert the following snippet:

services:
  schema-registry:
    image: hausgold/schema-registry
    environment:
      # Mind the .local suffix
      MDNS_HOSTNAME: schema-registry.local
      # Defaults to http://0.0.0.0:8081
      SCHEMA_REGISTRY_LISTENERS: http://0.0.0.0:8081
      # Defaults to kafka.local:9092
      SCHEMA_REGISTRY_KAFKASTORE_BOOTSTRAP_SERVERS: kafka.local:9092
      # Set the default Apache Avro schema compatibility
      #
      # See: http://bit.ly/2TcpoY1
      # See: http://bit.ly/2Hfo4wj
      SCHEMA_REGISTRY_AVRO_COMPATIBILITY_LEVEL: full
    ports:
      # The ports are just for you to know when configure your
      # container links, on depended containers
      - "80" # CORS-enabled nginx proxy to the schema-registry
      - "8081" # direct access to the schema-registry (no CORS)

  schema-registry-ui:
    image: hausgold/schema-registry-ui:0.9.5
    network_mode: bridge
    environment:
      MDNS_HOSTNAME: schema-registry-ui.local
      SCHEMAREGISTRY_URL: http://schema-registry.local

  kafka:
    image: hausgold/kafka
    environment:
      MDNS_HOSTNAME: kafka.local
      # See: http://bit.ly/2UDzgqI for Kafka downscaling
      KAFKA_HEAP_OPTS: -Xmx256M -Xms32M
    ulimits:
      # Due to systemd/pam RLIMIT_NOFILE settings (max int inside the
      # container), the Java process seams to allocate huge limits which result
      # in a +unable to allocate file descriptor table - out of memory+ error.
      # Lowering this value fixes the issue for now.
      #
      # See: http://bit.ly/2U62A80
      # See: http://bit.ly/2T2Izit
      nofile:
        soft: 100000
        hard: 100000

Afterwards start the service with the following command:

$ docker-compose up

Host configs

Install the nss-mdns package, enable and start the avahi-daemon.service. Then, edit the file /etc/nsswitch.conf and change the hosts line like this:

hosts: ... mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns ...

Configure a different mDNS hostname

The magic environment variable is MDNS_HOSTNAME. Just pass it like that to your docker run command:

$ docker run --rm -e MDNS_HOSTNAME=something.else.local hausgold/schema-registry

This will result in something.else.local.

You can also configure multiple aliases (CNAME's) for your container by passing the MDNS_CNAMES environment variable. It will register all the comma separated domains as aliases for the container, next to the regular mDNS hostname.

$ docker run --rm \
  -e MDNS_HOSTNAME=something.else.local \
  -e MDNS_CNAMES=nothing.else.local,special.local \
  hausgold/schema-registry

This will result in something.else.local, nothing.else.local and special.local.

Other top level domains

By default .local is the default mDNS top level domain. This images does not force you to use it. But if you do not use the default .local top level domain, you need to configure your host avahi to accept it.

Further reading

• Docker/mDNS demo: https://github.com/Jack12816/docker-mdns
• Archlinux howto: https://wiki.archlinux.org/index.php/avahi
• Ubuntu/Debian howto: https://wiki.ubuntuusers.de/Avahi/