Can the kafka connectors be configured via env variables passed when launching docker? Or curl is the only way?

Question

This is the docker image we use to host docker-connect with the plugins

FROM confluentinc/cp-kafka-connect:5.3.1

ENV CONNECT_PLUGIN_PATH=/usr/share/java

# JDBC-MariaDB
RUN wget -nv -P /usr/share/java/kafka-connect-jdbc/ https://downloads.mariadb.com/Connectors/java/connector-java-2.4.4/mariadb-java-client-2.4.4.jar

# SNMP Source
RUN wget -nv -P /tmp/ https://github.com/name/kafka-connect-snmp/releases/download/0.0.1.11/kafka-connect-snmp-0.0.1.11.tar.gz
RUN mkdir /tmp/kafka-connect-snmp && tar -xf /tmp/kafka-connect-snmp-0.0.1.11.tar.gz -C /tmp/kafka-connect-snmp/
RUN mv /tmp/kafka-connect-snmp/usr/share/kafka-connect/kafka-connect-snmp /usr/share/java/

I run this docker via docker-compose and then I have specified some common env variables defined here https://docs.confluent.io/current/installation/docker/config-reference.html#kafka-connect-configuration

But I also would like to specify connector related config from the env variable also, example I have done this

 - CONNECT_NAME=snmp-connector
 - CONNECT_CONNECTOR_CLASS=com.github.jcustenborder.kafka.connect.snmp.SnmpTrapSourceConnector
 - CONNECT_TOPIC=fm_snmp

What I am trying to do it, instead of calling

curl -X POST -H "Content-Type: application/json" --data '{"name":"","config":{"connector.class":"com.github.jcustenborder.kafka.connect.snmp.SnmpTrapSourceConnector","topic":"fm_snmp"}}' http://localhost:8083/connectors

I want to just specify it via env variables, BUT!! unfortunately its not working. So when I try seeing list of active connectors curl -localhost:8083/connectors/ , then I dont see it listed there.

So finally, my question can I configure it via env variables or only curl is the way?

Answer 1

You can't pass it as environment variables, but you can specify it as part of your Docker startup by passing in a custom command. Here's an example of doing it with Docker Compose. If you're calling docker run itself you'd need to rework this into an appropriate structure:

kafka-connect:
  image: confluentinc/cp-kafka-connect:5.3.1
  environment:
    CONNECT_REST_PORT: 18083
    CONNECT_REST_ADVERTISED_HOST_NAME: "kafka-connect"
    […]
  volumes:
    - $PWD/scripts:/scripts
  command: 
    - bash 
    - -c 
    - |
      /etc/confluent/docker/run & 
      echo "Waiting for Kafka Connect to start listening on kafka-connect ⏳"
      while [ $$(curl -s -o /dev/null -w %{http_code} http://kafka-connect:8083/connectors) -eq 000 ] ; do 
        echo -e $$(date) " Kafka Connect listener HTTP state: " $$(curl -s -o /dev/null -w %{http_code} http://kafka-connect:8083/connectors) " (waiting for 200)"
        sleep 5 
      done
      nc -vz kafka-connect 8083
      echo -e "\n--\n+> Creating Kafka Connect Elasticsearch sink"
      /scripts/create-es-sink.sh 
      sleep infinity

This calls a connector script, but if you want to embed it directly you can do it like this.