Preserve Kafka Connectors on `docker-compose down`?

Question

I followed Confluent's guides and made both the broker and zookeeper services use named volumes. Apparently, all of the connect service's data are on broker, so I don't need to make connect use a named volume.

However, when I run docker-compose down, then docker-compose up, none of the Kafka Connectors get restored. The topics get restored, so the named volumes are working for broker.

How can I make docker-compose down not delete the Kafka Connectors? Here's part of my docker-compose.yml:

---
version: '3.8'
services:
  zookeeper:
    image: confluentinc/cp-zookeeper:7.0.1
    container_name: zookeeper
    ports:
      - "2181:2181"
    restart: on-failure:3
    environment:
      ZOOKEEPER_CLIENT_PORT: 2181
      ZOOKEEPER_TICK_TIME: 2000
    volumes:
      - volume_zookeeper:/var/lib/zookeeper

  broker:
    image: confluentinc/cp-server:7.0.1
    container_name: broker
    depends_on:
      - zookeeper
    ports:
      - "9092:9092"
      - "9101:9101"
    restart: on-failure:3
    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_METRIC_REPORTERS: io.confluent.metrics.reporter.ConfluentMetricsReporter
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0
      KAFKA_CONFLUENT_LICENSE_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_CONFLUENT_BALANCER_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
      KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
      KAFKA_JMX_PORT: 9101
      KAFKA_JMX_HOSTNAME: localhost
      KAFKA_CONFLUENT_SCHEMA_REGISTRY_URL: http://schema-registry:8081
      CONFLUENT_METRICS_REPORTER_BOOTSTRAP_SERVERS: broker:29092
      CONFLUENT_METRICS_REPORTER_TOPIC_REPLICAS: 1
      CONFLUENT_METRICS_ENABLE: 'false'
      CONFLUENT_SUPPORT_CUSTOMER_ID: 'anonymous'
      CONFLUENT_REPORTERS_TELEMETRY_AUTO_ENABLE: 'false'
    volumes:
      - volume_kafka:/var/lib/kafka

  schema-registry:
    image: confluentinc/cp-schema-registry:7.0.1
    container_name: schema-registry
    depends_on:
      - broker
    ports:
      - "8081:8081"
    restart: on-failure:3
    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: kafka-connect-dockerfile:latest
    build:
      context: ./framework/infra
      dockerfile: ./kafka-connect-dockerfile
    container_name: connect
    depends_on:
      - broker
      - schema-registry
    ports:
      - "8083:8083"
    restart: on-failure:3
    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
      # CLASSPATH required due to CC-2422
      CLASSPATH: /usr/share/java/monitoring-interceptors/monitoring-interceptors-7.0.1.jar
      CONNECT_PRODUCER_INTERCEPTOR_CLASSES: "io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor"
      CONNECT_CONSUMER_INTERCEPTOR_CLASSES: "io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor"
      CONNECT_PLUGIN_PATH: "/usr/share/java,/usr/share/confluent-hub-components,/opt/kafka-connectors"
      CONNECT_LOG4J_LOGGERS: org.apache.zookeeper=ERROR,org.I0Itec.zkclient=ERROR,org.reflections=ERROR
      CONNECT_LOG4J_ROOT_LOGLEVEL: 'WARN'
      CONNECT_TOOLS_LOG4J_LOGLEVEL: 'WARN'
      CONNECT_REST_PORT: 8083
    volumes:
      - ./framework/infra/kafka-connectors/jars:/opt/kafka-connectors

volumes:
  volume_zookeeper:
    driver: local
    driver_opts:
      type: none
      o: bind
      device: /var/lib/zookeeper

  volume_kafka:
    driver: local
    driver_opts:
      type: none
      o: bind
      device: /var/lib/kafka

Answer 1

Kafka Connect connectors are stateless. All their data is stored in Kafka, in the 3 topics defined in the container environment variables

Therefore, you'll need to ensure your mounted volumes for Kafka and Zookeeper are not deleted upon restarts