with this docker-compose configuration, why is 8080 considered used? - docker

Question

to set the context, i have a very basic kafka server setup through a docker-compose.yml file, and then i spin up a ui app for kafka.
depending on the config, the ui app will/wont work becuase of port 8080 being used/free.
my question is how does 8080 tie into this, when the difference between working and non working configs is the host ip.
btw this is done in wsl (with the wsl ip being the ip in question 172.20.123.69.)
ui app:
podman run \
--name kafka_ui \
-p 8080:8080 \
-e KAFKA_CLUSTERS_0_NAME=local \
-e KAFKA_CLUSTERS_0_BOOTSTRAPSERVERS=172.20.123.69:9092 \
-d provectuslabs/kafka-ui:latest
ui works with this kafka server config:
version: "2"
services:
zookeeper:
container_name: zookeeper-server
image: docker.io/bitnami/zookeeper:3.8
ports:
- "2181:2181"
volumes:
- "/home/rndom/volumes/zookeeper:/bitnami/zookeeper"
environment:
- ALLOW_ANONYMOUS_LOGIN=yes
kafka:
container_name: kafka-server
image: docker.io/bitnami/kafka:3.3
ports:
- "9092:9092"
volumes:
- "/home/rndom/volumes/kafka:/bitnami/kafka"
environment:
- KAFKA_BROKER_ID=1
- KAFKA_CFG_LISTENERS=PLAINTEXT://:9092
- KAFKA_CFG_ADVERTISED_LISTENERS=PLAINTEXT://172.20.123.69:9092
- KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181
- ALLOW_PLAINTEXT_LISTENER=yes
depends_on:
- zookeeper
volumes:
zookeeper_data:
driver: bridge
kafka_data:
driver: bridge
networks:
downloads_default:
driver: bridge
notice the environment variable KAFKA_CFG_ADVERTISED_LISTENERS has the wsl ip.
ui doesn't work with the following:
version: "2"
services:
zookeeper:
container_name: zookeeper-server
image: docker.io/bitnami/zookeeper:3.8
ports:
- "2181:2181"
volumes:
- "/home/rndom/volumes/zookeeper:/bitnami/zookeeper"
environment:
- ALLOW_ANONYMOUS_LOGIN=yes
kafka:
container_name: kafka-server
image: docker.io/bitnami/kafka:3.3
ports:
- "9092:9092"
volumes:
- "/home/rndom/volumes/kafka:/bitnami/kafka"
environment:
- KAFKA_BROKER_ID=1
- KAFKA_CFG_LISTENERS=PLAINTEXT://:9092
- KAFKA_CFG_ADVERTISED_LISTENERS=PLAINTEXT://:9092
- KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181
- ALLOW_PLAINTEXT_LISTENER=yes
depends_on:
- zookeeper
volumes:
zookeeper_data:
driver: bridge
kafka_data:
driver: bridge
networks:
downloads_default:
driver: bridge
the latter i got from the official bitnami docker hub repo.
the error i get when i use it:
*************************
APPLICATION FAILED TO START
*************************
etc etc.
Web server failed to start Port 8080 was already in use
Since i got it to work, this is really just for my own understanding.

Answer 1

Do use KAFKA_CFG_ADVERTISED_LISTENERS=PLAINTEXT://kafka:9092
Don't use podman run for one container. Put the UI container in the same compose file
Use KAFKA_CLUSTERS_0_BOOTSTRAPSERVERS=kafka:9092
If you still get errors, then as the error says, the port is occupied, so use a different one like 8081:8080. That has nothing to do with the Kafka setup.
This Compose file works fine for me
version: "2"
services:
zookeeper:
image: docker.io/bitnami/zookeeper:3.8
environment:
- ALLOW_ANONYMOUS_LOGIN=yes
kafka:
image: docker.io/bitnami/kafka:3.3
environment:
- KAFKA_BROKER_ID=1
- KAFKA_CFG_LISTENERS=PLAINTEXT://0.0.0.0:9092
- KAFKA_CFG_ADVERTISED_LISTENERS=PLAINTEXT://kafka:9092
- KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181
- ALLOW_PLAINTEXT_LISTENER=yes
depends_on:
- zookeeper
kafka_ui:
image: docker.io/provectuslabs/kafka-ui:latest
ports:
- 8080:8080
environment:
- KAFKA_CLUSTERS_0_NAME=local
- KAFKA_CLUSTERS_0_BOOTSTRAPSERVERS=kafka:9092

Answer 2

try the command "netstat -tupan" and check if 8080 is not used by any other process.