Unable to create topic with underscore "_"

[shreyasarani23]

Following is my topic configuration

apiVersion: kafka.strimzi.io/v1beta2
kind: KafkaTopic
metadata:
  name: app_launch
spec:
  partitions: 3
  replicas: 3
  config:
    min.insync.replicas: 2

when I try to create the topic I get the following error. Does strimzi doesn't allow to have underscore in topic name?

 kubectl apply -f t1.yaml -n kafka
The KafkaTopic "app_launch" is invalid: metadata.name: Invalid value: "app_launch": a DNS-1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')

while I am able to create same topic on kafka CLI but with warning

[kafka@my-kafka-cluster-kafka-0 kafka]$ bin/kafka-topics.sh --create --topic app_launch --bootstrap-server my-kafka-cluster-kafka-bootstrap:9092
WARNING: Due to limitations in metric names, topics with a period ('.') or underscore ('_') could collide. To avoid issues it is best to use either, but not both.
Created topic app_launch.

[scholzj]

Please read the documentation: https://strimzi.io/docs/operators/latest/full/using.html#kafka_topic_naming_conventions

[shreyasarani23]

well the topic is in ready state by decreasing replica and min.insync.replia.

~/kafka-deployment/teplay-times2$ kubectl get KafkaTopic -n kafka
NAME                                                                                               CLUSTER            PARTITIONS   REPLICATION FACTOR   READY
app-launch---4d30c079b7634594a874ab17cf99fb76eb8091ee                                              my-kafka-cluster   1            1                    True
consumer-offsets---84e7a678d08f4bd226872e5cdd4eb527fadc1c6a                                        my-kafka-cluster   50           1                    True
demo-topic-1                                                                                       my-kafka-cluster   3            2                    True
demo-topic-2                                                                                       my-kafka-cluster   3            2                    True
my-topic                                                                                           my-kafka-cluster   3            2                    True
strimzi-store-topic---effb8e3e057afce1ecf67c3f5d8e4e3ff177fc55                                     my-kafka-cluster   1            2                    True
strimzi-topic-operator-kstreams-topic-store-changelog---b75e702040b99be8a9263134de3507fc0cc4017b   my-kafka-cluster   1            1                    True
test-topic                                                                                         my-kafka-cluster   4            2                    True
topic-name-1                                                                                       my-kafka-cluster   2            2                    True
shreyas@Azure:~/kafka-deployment/teplay-times2$ kubectl exec -it my-kafka-cluster-kafka-1 -n kafka -- /bin/bash
[kafka@my-kafka-cluster-kafka-1 kafka]$ bin/kafka-topics.sh --list --bootstrap-server my-kafka-cluster-kafka-bootstrap:9092
__consumer_offsets
__strimzi-topic-operator-kstreams-topic-store-changelog
__strimzi_store_topic
app_launch
demo-topic-1
demo-topic-2
my-topic
test-topic
topicName-1

Sorry I am asking you again but I am getting confused with the topic name. when I do kubectl get KafkaTopic -n kafka it shows the topic name as topic-name-1.

But when I list the topics on kafka CLI it shows topicName-1. so what is the actual topic name is it topic-name-1 or topicName-1 . metadata.name and spec.topicName how are they different can you please explain?

[scholzj]

kubectl get KafkaTopic -n kafka shows the KafkaTopic resources. So the name column is the name of the resource (.metadata.name).

[shreyasarani23]

So the actual name of the topic is topicName-1 in this case right?

[scholzj]

Yes ... you can also see it in your list of Kafka topics directly from Kafka.

[shreyasarani23]

Thanks @scholzj for clarifying my doubt. It's really great you are helping so many people. keep up the good work.