Fix Kafka Client List Topics Method

[nasark]

This method uses the rdkafka admin API to retrieve metadata from the kafka server. This is a good way to perform health checks since if the kafka server is down, this will return an error instead.

@miq-bot assign @agrare
@miq-bot add_reviewer @agrare
@miq-bot add_label enhancement

[nasark]

We will need a new release of this gem once this is merged

[agrare]

You should be able to use ::Rdkafka::Config#admin method here rather than having to use instance_variable_get, https://github.com/karafka/rdkafka-ruby/blob/main/lib/rdkafka/config.rb#L263-L286

Suggested change

	native_kafka = producer.instance_variable_get(:@native_kafka)
	Rdkafka::Admin.new(native_kafka).metadata
	@kafka_client.admin.metadata

[agrare]

@nasark I think we can use this method if we use:

Suggested change

	Rdkafka::Metadata.new(native_kafka).topics.collect { |topic| topic[:topic_name] }
	kafka_client.admin.metadata.topics.map { |topic| topic[:topic_name] }

[agrare]

I think "metadata" is a little vague and would be hard to implement for the other messaging types, where listing queues/topics could likely be done.

I think we'd be better off fixing the "topics" method above, possibly implement an alive? method that catches Local: Broker transport failure (transport) (Rdkafka::RdkafkaError) and returns false and we could use that for the health-check, wdyt?

[nasark]

So we catch errors in the top level health check method which basically does the same thing https://github.com/ManageIQ/manageiq/blob/master/app/models/miq_server.rb#L632, or is it better to catch here?

[nasark]

also in manageiq-messaging-ready https://github.com/ManageIQ/manageiq-appliance/blob/master/COPY/usr/bin/manageiq-messaging-ready#L35

[agrare]

So we catch errors in the top level health check method which basically does the same thing

Yeah that's fine for now, I don't like exposing "internal" exception classes like RdkafkaError to the caller but we already do that elsewhere in this class. Ideally we'd catch RdkafkaError and wrap it in a ManageIQ::Messaging::Error class but that's a larger effort.

[agrare]

Released v1.4.2 https://github.com/ManageIQ/manageiq-messaging/releases/tag/v1.4.2 with this change

[nasark]

Follow up #89