Cannot connect to kafka which is outside of network - docker

Question

I'm trying to connect my job inside a container which sends events to kafka cluster in another container.
No matter what i've tried, i can't send the event to kafka topic
I 've tried telnet and kafkacat to the address listener port of my kafka, everything works just fine:
Telnet output
Kafkacat output
This is my job compose file, "172.16.33.91" is my local ip address:
version: '3'
services:
events-processor:
build:
context: ./events-processor
extra_hosts:
- "host:172.16.33.91"
restart: unless-stopped
This is my job code, which sends data from 1 -> 1000 to a existed topic num-test:
from time import sleep
from json import dumps
from kafka import KafkaProducer
if __name__=="__main__":
producer = KafkaProducer(bootstrap_servers=['host:9093'],
value_serializer=lambda x: dumps(x).encode('utf-8'))
for e in range(1000):
data = {'number' : e}
producer.send('numtest', value=data)
print(data)
sleep(5)
This is my kafka-zookeeper compose file:
version: '3'
services:
zookeeper:
image: confluentinc/cp-zookeeper
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000
volumes:
- zk-data:/var/lib/zookeeper/data
- zk-logs:/var/lib/zookeeper/log
- secrets:/etc/zookeeper/secrets
restart: unless-stopped
kafka:
image: confluentinc/cp-kafka
depends_on:
- zookeeper
ports:
- "9093:9093"
environment:
KAFKA_BROKER_ID: 1
KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka:9092,EXTERNAL://:9093
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INTERNAL:PLAINTEXT,EXTERNAL:PLAINTEXT
KAFKA_LISTENERS: INTERNAL://:9092,EXTERNAL://:9093
KAFKA_ZOOKEEPER_CONNECT: 'zookeeper:2181'
KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
volumes:
- kafka-data:/var/lib/kafka/data
- secrets:/etc/kafka/secrets
restart: unless-stopped
volumes:
zk-logs: {}
zk-data: {}
kafka-data: {}
secrets: {}
Anyone have any idea what've i done wrong? Any help appreciated!!!

Answer 1

I remembering encountering a similar issue with connectivity. Turns out, for your container to be able to access the ports on your host machine, you may need to add additional rules to your firewall to open it up.
For example with iptables, you can add a rule like the below to allow your host machine to accept requests from your docker containers.
-A INPUT -i docker0 -j ACCEPT
Alternatively, you can put your job container on the same docker network as your kafka/zookeeper. Either by putting your application in the same docker-compose file, or using a common external docker network.

Answer 2

If there is a better place this information should be put, or keywords you're missing to find the solutions, let the community know
Multiple blogs are written on this already
KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka:9092,HOST://localhost:9093
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INTERNAL:PLAINTEXT,HOST:PLAINTEXT
KAFKA_LISTENERS: INTERNAL://0.0.0.0:9092,HOST://0.0.0.0:9093
Using ://:port address will only listen to the local hostname, container or not
You must listen to external connections by binding to all interfaces, 0.0.0.0
You must advertise internally and/or any external hostnames

Answer 3

Here is another Working Sample :
version: '2'
services:
zookeeper1:
image: confluentinc/cp-zookeeper:$CP_VERSION
container_name: zookeeper1
hostname: zookeeper1
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000
ZOOKEEPER_SERVER_ID: 1
ZOOKEEPER_SERVERS: "zookeeper1:22888:23888;zookeeper2:22888:23888;zookeeper3:22888:23888"
ports:
- 2181:2181
volumes:
- ./data/zoo-1/data:/var/lib/zookeeper/data
- ./data/zoo-1/log:/var/lib/zookeeper/log
zookeeper2:
image: confluentinc/cp-zookeeper:$CP_VERSION
container_name: zookeeper2
hostname: zookeeper2
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000
ZOOKEEPER_SERVER_ID: 2
ZOOKEEPER_SERVERS: "zookeeper1:22888:23888;zookeeper2:22888:23888;zookeeper3:22888:23888"
ports:
- 2182:2181
volumes:
- ./data/zoo-2/data:/var/lib/zookeeper/data
- ./data/zoo-2/log:/var/lib/zookeeper/log
zookeeper3:
image: confluentinc/cp-zookeeper:$CP_VERSION
container_name: zookeeper3
hostname: zookeeper3
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000
ZOOKEEPER_SERVER_ID: 3
ZOOKEEPER_SERVERS: "zookeeper1:22888:23888;zookeeper2:22888:23888;zookeeper3:22888:23888"
ports:
- 2183:2181
volumes:
- ./data/zoo-3/data:/var/lib/zookeeper/data
- ./data/zoo-3/log:/var/lib/zookeeper/log
kafka1:
image: confluentinc/cp-kafka:$CP_VERSION
container_name: kafka1
hostname: kafka1
depends_on:
- zookeeper1
- zookeeper2
- zookeeper3
ports:
- 9091:9091
environment:
KAFKA_BROKER_ID: 1
KAFKA_ZOOKEEPER_CONNECT: zookeeper1:2181,zookeeper2:2181,zookeeper3:2181
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INTERNAL:PLAINTEXT,OUTSIDE:PLAINTEXT
KAFKA_LISTENERS: INTERNAL://:29092,OUTSIDE://:9091
KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka1:29092,OUTSIDE://kafka1:9091
KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
KAFKA_LOG_DIRS: /var/lib/kafka/logs
kafka2:
image: confluentinc/cp-kafka:$CP_VERSION
container_name: kafka2
hostname: kafka2
depends_on:
- zookeeper1
- zookeeper2
- zookeeper3
ports:
- 9092:9092
environment:
KAFKA_BROKER_ID: 2
KAFKA_ZOOKEEPER_CONNECT: zookeeper1:2181,zookeeper2:2181,zookeeper3:2181
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INTERNAL:PLAINTEXT,OUTSIDE:PLAINTEXT
KAFKA_LISTENERS: INTERNAL://:29092,OUTSIDE://:9092
KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka2:29092,OUTSIDE://kafka2:9092
KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
KAFKA_LOG_DIRS: /var/lib/kafka/logs
kafka3:
image: confluentinc/cp-kafka:$CP_VERSION
container_name: kafka3
hostname: kafka3
depends_on:
- zookeeper1
- zookeeper2
- zookeeper3
ports:
- 9093:9093
environment:
KAFKA_BROKER_ID: 3
KAFKA_ZOOKEEPER_CONNECT: zookeeper1:2181,zookeeper2:2181,zookeeper3:2181
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INTERNAL:PLAINTEXT,OUTSIDE:PLAINTEXT
KAFKA_LISTENERS: INTERNAL://:29092,OUTSIDE://:9093
KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka3:29092,OUTSIDE://kafka3:9093
KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
KAFKA_LOG_DIRS: /var/lib/kafka/logs
dont forget to edit /etc/hosts and the proper hostnames to ba able to work with above kafka cluster outside the Docker.
my /etc/hosts file is shown below :
127.0.0.1 localhost
127.0.0.1 kafka1
127.0.0.1 kafka2
127.0.0.1 kafka3