First, you need to install Java because Kafka depends of it and then install Kafka:
brew install java
brew install kafka
Before of all we need to have runnig Kafka, to do that first start with Zookeeper with this command brew services start zookeeper and finally Kafka with brew services start kafka, at this point we have running Kafka in local.
In our Rails app console we need to run the Karafka server with this bundle exec karafka server.
Here we can do some tests:
> rails c
UsersResponder.call({ event_name: "user_created", payload: { id: 1 } })
# Output
[2021-02-16T22:47:53.200369 #12763] INFO -- : Sending 1 messages to 192.168.1.77:9092 (node_id=0)
D, [2021-02-16T22:47:53.200846 #12763] DEBUG -- : [produce] Opening connection to 192.168.1.77:9092 with client id delivery_boy...
D, [2021-02-16T22:47:53.201818 #12763] DEBUG -- : [produce] Sending produce API request 1 to 192.168.1.77:9092
D, [2021-02-16T22:47:53.443563 #12763] DEBUG -- : [produce] Waiting for response 1 from 192.168.1.77:9092
D, [2021-02-16T22:47:53.456032 #12763] DEBUG -- : [produce] Received response 1 from 192.168.1.77:9092
D, [2021-02-16T22:47:53.456735 #12763] DEBUG -- : Successfully appended 1 messages to users/0 on 192.168.1.77:9092 (node_id=0)
=> {"users"=>[["{\"event_name\":\"user_created\",\"payload\":{\"id\":1}}", {:topic=>"users"}]]}
> bundle exec karafka server
# Output
New [User] event: #<Karafka::Params::Params:0x00007fe1044d99b8>
Inline processing of topic users with 1 messages took 0 ms
1 message on users topic delegated to UsersConsumer
[[karafka_example_example] {}:] Marking users/0:0 as processed
[[karafka_example_example] {}:] Committing offsets with recommit: users/0:1
[[karafka_example_example] {}:] [offset_commit] Sending offset_commit API request 13 to 192.168.1.77:9092