Why i can't access kafka from an external machine? - docker

Question

I am new to kafka, i tried to setup my first cluster on a vps with Docker-compose. But i still cannot access it from my local pc ( outside the host ).
here is my docker compose
version: '2'
services:
zookeeper-1:
image: confluentinc/cp-zookeeper:latest
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000
ports:
- 22181:2181
zookeeper-2:
image: confluentinc/cp-zookeeper:latest
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000
ports:
- 32181:2181
kafka-1:
image: confluentinc/cp-kafka:latest
depends_on:
- zookeeper-1
- zookeeper-2
ports:
- 29092:29092
environment:
KAFKA_BROKER_ID: 1
KAFKA_ZOOKEEPER_CONNECT: zookeeper-1:2181,zookeeper-2:2181
KAFKA_LISTENERS: EXTERNAL_SAME_HOST://:29092,EXTERNAL_DIFFERENT_HOST://:29093,INTERNAL://:9092
KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka:9092,EXTERNAL_SAME_HOST://localhost:29092,EXTERNAL_DIFFERENT_HOST://XXX.XXX.XXX.XXX:29093
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INTERNAL:PLAINTEXT,EXTERNAL_SAME_HOST:PLAINTEXT,EXTERNAL_DIFFERENT_HOST:PLAINTEXT
KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
kafka-2:
image: confluentinc/cp-kafka:latest
depends_on:
- zookeeper-1
- zookeeper-2
ports:
- 39092:39092
environment:
KAFKA_BROKER_ID: 2
KAFKA_ZOOKEEPER_CONNECT: zookeeper-1:2181,zookeeper-2:2181
KAFKA_LISTENERS: EXTERNAL_SAME_HOST://:39092,EXTERNAL_DIFFERENT_HOST://:39093,INTERNAL://:9093
KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka:9093,EXTERNAL_SAME_HOST://localhost:39092,EXTERNAL_DIFFERENT_HOST://XXX.XXX.XXX.XXX:39093
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INTERNAL:PLAINTEXT,EXTERNAL_SAME_HOST:PLAINTEXT,EXTERNAL_DIFFERENT_HOST:PLAINTEXT
KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
I searched in the logs and i found that there is no available brokers ( always 0 ) because the server couldn't connect to "kafka:9092" AND Zookeeper keep failing to connect to the brokers.
[2022-04-13 14:56:59,422] WARN Session 0x0 for sever My-vps-URL/XXX.XXX.XXX.XXX:2181, Closing socket connection. Attempting reconnect except
it is a SessionExpiredException. (org.apache.zookeeper.ClientCnxn)
org.apache.zookeeper.ClientCnxn$SessionTimeoutException: Client session timed out, have not
heard from server in 30006ms for session id 0x0
at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1258)
KeeperErrorCode = ConnectionLoss for /brokers/ids
How can i fix this ?
Note that i tried a similar config with a different docker image ( bitnami's ), and with different cluster config ( 1 zookeeper 1 broker ) and it still doesn't work.

Answer 1

You have a Zookeeper error because you are running an even number of them. The number of Zookeepers doesn't need to match the number of brokers, and it should be an odd number of them, only, up to 7 max. You also shouldn't need ports on the Zookeeper servers.
For your Kafka Connection,
KAFKA_LISTENERS needs to include the IP of 0.0.0.0 to allow for the server to bind on all interfaces
You need to expose port 29093 and 39093 since those are your "different host" settings. You currently only have ports to connect from the same machine.
your clients need to connect to the EXTERNAL_DIFFERENT_HOST address you've set, not kafka:9092
Further reading - Connect to Kafka running in Docker
tried a similar config with a different docker image ( bitnami's )
That image has different variables, but same basic answer as above.
different cluster config ( 1 zookeeper 1 broker )
There is little benefit of running multiple of each of those on the same machine, so I suggest trying to get that configuration working, first.