带有 Python 消费者的 Docker Kafka

Question

I am using dockerized Kafka and written one Kafka consumer program. It works perfectly when I run Kafka in docker and application at my local machine. But when I configured the local application in docker I am facing issues. The issue may be due to a topic not created until time application started.

docker-compose.yml

version: '3'
services:
  zookeeper:
    image: wurstmeister/zookeeper
    ports:
      - "2181:2181"
  kafka:
    image: wurstmeister/kafka
    ports:
      - "9092:9092"
    environment:
      KAFKA_ADVERTISED_HOST_NAME: localhost
      KAFKA_CREATE_TOPICS: "test:1:1"
      KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
  parse-engine:
    build: .
    depends_on:
      - "kafka"
    command: python parse-engine.py
    ports:
     - "5000:5000"

parse-engine.py

from kafka import KafkaConsumer
import json

try:
    print('Welcome to parse engine')
    consumer = KafkaConsumer('test', bootstrap_servers='localhost:9092')
    for message in consumer:
        print(message)
except Exception as e:
    print(e)
    # Logs the error appropriately. 
    pass

Error log

kafka_1         | [2018-09-21 06:27:17,400] INFO [SocketServer brokerId=1001] Started processors for 1 acceptors (kafka.network.SocketServer)
kafka_1         | [2018-09-21 06:27:17,404] INFO Kafka version : 2.0.0 (org.apache.kafka.common.utils.AppInfoParser)
kafka_1         | [2018-09-21 06:27:17,404] INFO Kafka commitId : 3402a8361b734732 (org.apache.kafka.common.utils.AppInfoParser)
kafka_1         | [2018-09-21 06:27:17,431] INFO [KafkaServer id=1001] started (kafka.server.KafkaServer)
**parse-engine_1  | Welcome to parse engine
parse-engine_1  | NoBrokersAvailable 
parseengine_parse-engine_1 exited with code 0**
kafka_1         | creating topics: test:1:1

As I already added depends_on property in docker-compose but before starting topic application connecting so error occurred.

I read that I can possible to add the script in the docker-compose file but I am looking for some easy way.

Thanks for help

Answer 1

Your problem is the networking. In your Kafka config you're setting

KAFKA_ADVERTISED_HOST_NAME: localhost

but this means that any client (including your python app) will connect to the broker, and then be told by the broker to use localhost for any connections. Since localhost from your client machine (eg your python container) is not where the broker is, requests will fail.

You can read more about fixing problems with your Kafka listeners in detail here

• Kafka Listeners - Explained
• My Python/Java/Spring/Go/Whatever Client Won't Connect to My Apache Kafka Cluster in Docker/AWS/My Brother's Laptop. Please Help!

So to fix your issue, you can do one of two things:

1. Simply change your compose to use the internal hostname for Kafka ( KAFKA_ADVERTISED_HOST_NAME: kafka ). This means any clients within the docker network will be able to access it fine, but no external clients will be able to (eg from your host machine):

    version: '3' services: zookeeper: image: wurstmeister/zookeeper ports: - "2181:2181" kafka: image: wurstmeister/kafka ports: - "9092:9092" environment: KAFKA_ADVERTISED_HOST_NAME: kafka KAFKA_CREATE_TOPICS: "test:1:1" KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181 volumes: - /var/run/docker.sock:/var/run/docker.sock parse-engine: build: . depends_on: - "kafka" command: python parse-engine.py ports: - "5000:5000"

   Your clients would then access the broker at kafka:9092, so your python app would change to

    consumer = KafkaConsumer('test', bootstrap_servers='kafka:9092')

2. Add a new listener to Kafka. This enables it to be accessed both internally and externally to the docker network. Port 29092 would be for access external to the docker network (eg from your host), and 9092 for internal access.

   You would still need to change your python program to access Kafka at the correct address. In this case since it's internal to the Docker network, you'd use:

    consumer = KafkaConsumer('test', bootstrap_servers='kafka:9092')

   Since I'm not familiar with the wurstmeister images, this docker-compose is based on the Confluent images which I do know:

   (editor has mangled my yaml, you can find it here )

    --- version: '2' services: zookeeper: image: confluentinc/cp-zookeeper:latest environment: ZOOKEEPER_CLIENT_PORT: 2181 ZOOKEEPER_TICK_TIME: 2000 kafka: # "`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,- # An important note about accessing Kafka from clients on other machines: # ----------------------------------------------------------------------- # # The config used here exposes port 29092 for _external_ connections to the broker # ie those from _outside_ the docker network. This could be from the host machine # running docker, or maybe further afield if you've got a more complicated setup. # If the latter is true, you will need to change the value 'localhost' in # KAFKA_ADVERTISED_LISTENERS to one that is resolvable to the docker host from those # remote clients # # For connections _internal_ to the docker network, such as from other services # and components, use kafka:9092. # # See https://rmoff.net/2018/08/02/kafka-listeners-explained/ for details # "`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,-'"`-._,- # image: confluentinc/cp-kafka:latest depends_on: - zookeeper ports: - 29092:29092 environment: KAFKA_BROKER_ID: 1 KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181 KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://kafka:9092,PLAINTEXT_HOST://localhost:29092 KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT KAFKA_INTER_BROKER_LISTENER_NAME: PLAINTEXT KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1

---

Disclaimer: I work for Confluent

Answer 2

This line

KAFKA_ADVERTISED_HOST_NAME: localhost

Says the broker is advertising itself as being available only on localhost , which means all Kafka clients would only get back itself, not the actual list of real broker addresses. This would be fine if your clients are only located on your host - requests always go to localhost, which is forwarded to the container .

But, for apps in other containers, they need to point at the Kafka container, so it should say KAFKA_ADVERTISED_HOST_NAME: kafka , where kafka here is the name of the Docker Compose Service. Then clients in other containers would try to connect to that one

---

That being said, then, this line

consumer = KafkaConsumer('test', bootstrap_servers='localhost:9092')

You are pointing the Python container at itself , not the kafka container.

It should say kafka:9092 instead

Answer 3

In my case I wanted to access the Kafka Container from an external python client running locally (as a producer) and here is the combination of containers and python code that worked for me (Platform MAC OS and docker version 2.4.0):

zookeeper container:

docker run -d \
-p 2181:2181 \
--name=zookeeper \
-e ZOOKEEPER_CLIENT_PORT=2181 \
confluentinc/cp-zookeeper:5.2.3

kafka container:

docker run -d \ 
-p 29092:29092 \ 
-p 9092:9092 \ 
--name=kafka \ 
-e KAFKA_ZOOKEEPER_CONNECT=host.docker.internal:2181 \ 
-e KAFKA_LISTENER_SECURITY_PROTOCOL_MAP=BROKER:PLAINTEXT,PLAINTEXT:PLAINTEXT \ 
-e KAFKA_ADVERTISED_LISTENERS=PLAINTEXT://kafka:29092,BROKER://localhost:9092 \ 
-e KAFKA_INTER_BROKER_LISTENER_NAME=BROKER \ 
-e KAFKA_BROKER_ID=1 \ 
-e KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR=1 \ 
-e KAFKA_CREATE_TOPICS="test:1:1" \ 
confluentinc/cp-enterprise-kafka:5.2.3

python client:

from kafka import KafkaProducer
import json
producer = KafkaProducer(bootstrap_servers=['localhost:29092'],
value_serializer=lambda v: json.dumps(v).encode('utf-8'),
security_protocol='PLAINTEXT')
acc_ini = 523416
print("Sending message")
producer.send('test', {'model_id': '1','acc':str(acc_ini), 'content':'test'})
producer.flush()

Answer 4

In my local setup, I had the same issue where all the containers were working fine inside the docker but the connectors were unable to connect to the Kafka.

My Kafka configuration inside docker-compose.yml :

  broker:
    image: confluentinc/cp-server:7.0.1
    hostname: broker
    container_name: broker
    depends_on:
      - zookeeper
    ports:
      - "29092:29092"
      - "9092:9092"
    environment:
      KAFKA_BROKER_ID: 1
      KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
      KAFKA_LISTENERS: INTERNAL://:29092,EXTERNAL://:9092
      KAFKA_ADVERTISED_LISTENERS: INTERNAL://:29092,EXTERNAL://:9092
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INTERNAL:PLAINTEXT,EXTERNAL:PLAINTEXT
      KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL

Based on google responses I tried localhost:port , 127.0.0.1:port , and 0.0.0.0:port as the URL in my connector config but nothing worked.

Eventually, I had to pass the actual IP address of my local system and it worked. I'm using Docker on Windows 10.

ActiveMQ Connector congif:

{
  "connector.class": "io.confluent.connect.activemq.ActiveMQSourceConnector",
  "activemq.url": "tcp://<my-system-ip>:61616", <-- my system's IP address
  "max.poll.duration": "60000",
  "tasks.max": "1",
  "batch.size": "1",
  "name": "activemq-jms-connector",
  "jms.destination.name": "jms-test",
  "kafka.topic": "topic-1",
  "activemq.password": "password",
  "jms.destination.type": "topic",
  "use.permissive.schema": "false",
  "activemq.username": "username"
}

I hope this will help anyone struggling with the Kafka-connect setup on Windows and Docker.