Java Kafka Client fails to connect to docker image

[loopingrage]

I spun up an instance of vectorized/redpanda:latest and tried connecting from the my Docker host using the standard Java client. This is what I see in my application log:

Connection to node 1 (/0.0.0.0:9092) could not be established.

I believe this is due to the fact that the Java client connects to redpanda as a bootsrtap and as part of the Kafka protocol handshake it is give the address to the actual broker which in this case seems to resolve to 0.0.0.0.

This is from the docker logs:

kafka                  | INFO  2020-11-18 05:31:30,439 [shard 0] redpanda::main - application.cc:162 - advertised_kafka_api:{nullopt}	- Address of Kafka API published to the clients
....
kafka                  | INFO  2020-11-18 05:31:30,440 [shard 0] redpanda::main - application.cc:162 - kafka_api:{host: 0.0.0.0, port: 9092}	- Address and port of an interface to listen for Kafka API requests

I'm migrating my app from Apache Kafka and for my existing config I had to specify some environment variables to get the bootstrap process to work including:

KAFKA_CFG_LISTENER_SECURITY_PROTOCOL_MAP=CLIENT:PLAINTEXT,EXTERNAL:PLAINTEXT
KAFKA_CFG_LISTENERS=CLIENT://:9092,EXTERNAL://:9093
KAFKA_CFG_ADVERTISED_LISTENERS=CLIENT://kafka:9092,EXTERNAL://localhost:9093

Note the support for multiple ports mapping to different host names. This was needed to work in both docker compose where the host name for the kafka container was literally kafka and when connecting from the host using an exposed port.

Does your Docker image have support for similar ENV configs? The redpanda docker image on Docker Hub doesn't have a README yet (I know you're working on one).

[BenPope]

advertised_kafka_api needs to be set. Instead of using the docker standalone, it might be easier to use rpk container start -n 3, which will set things up properly: https://vectorized.io/rpk-container/

[dotnwat]

we should probably consider exposing similar configurations via environment variable, perhaps even 1-1 with the kafka environment variables if there is a strong connection between configurations. it would seem to make sense for this sort of network configuration.

[dotnwat]

@loopingrage we're working on the issue related to advertised host in #125. in the meantime, i was able to get the java client to connect successfully to redpanda running in docker using host networking, if that is an option for you:

docker run --network=host vectorized/redpanda:latest
bin/kafka-topics.sh --bootstrap-server 127.0.0.1:9092 --list

[loopingrage]

I'm running within a Docker Compose environment so host networking unfortunately does not work in my case. The rpk container option won't work for the same reason.

Just a thought. Is there a way to mount my own redpanda config file into the container? If you place the config file in its own directory that would be it pretty easy for me to do using a a Docker Compose volume that mounts a config on the Docker host. We do this for our own software where environment variables are not flexible enough to express the multitude of config options.

[dotnwat]

@loopingrage yes, @0x5d i think has some instructions to make this volume mount + config trick work until #125 lands.

[loopingrage]

Any thoughts @0x5d?

[0x5d]

Hi @loopingrage. You can put the config file (redpanda.yaml) in a directory and mount it into /etc/redpanda/ on the container.

You can use this as a template (complete reference: https://vectorized.io/documentation/advanced-configuration/):

config_file: /etc/redpanda/redpanda.yaml
redpanda:
  admin:
    address: 0.0.0.0
    port: 9644
  advertised_kafka_api:
    address: 127.0.0.1
    port: 45677
  advertised_rpc_api:
    address: <container hostname>
    port: 33145
  data_directory: /var/lib/redpanda/data
  developer_mode: true
  kafka_api:
    address: <container hostname>
    port: 9092
  kafka_api_tls:
    cert_file: ""
    enabled: false
    key_file: ""
    truststore_file: ""
  node_id: <node id>
  rpc_server:
    address: <container hostname>
    port: 33145
  seed_servers: []
  auto_create_topics_enabled: true

rpk:
  enable_usage_stats: true
  tune_network: false
  tune_disk_scheduler: false
  tune_disk_nomerges: false
  tune_disk_irq: false
  tune_fstrim: false
  tune_cpu: false
  tune_aio_events: false
  tune_clocksource: false
  tune_swappiness: false
  enable_memory_locking: false
  tune_coredump: false

[rk3rn3r]

I start a single node Redpanda container with docker compose like that:

version: '2'
services:
  kafka:
    image: vectorized/redpanda:latest
    hostname: kafka
    ports:
     - 9092:9092
    command: ["start", "--advertise-kafka-addr", "kafka:9092"]

And it works well with Kafka Connect Distributed.
FYI @senior7515 ;)

[dotnwat]

excellent @rk3rn3r @loopingrage multi-network support just landed in the core so we now supported named listeners like you expect in kafka. that's being wired up right now through rpk tooling #529

[BenPope]

Closing this as multi-listener is now configurable from config file and command line args. Please open a new issue if there are still issues.

[rk3rn3r]

@BenPope @dotnwat nice! I will test soon 🤞