Why do I require fabric-kafka and fabric-order containers in same network

Question

I have read the following doc to understand the Ordering Service: https://github.com/hyperledger/fabric/blob/master/orderer/README.md

What I don't understand is why fabric-kafka and fabric-orderer docker images are present in the network. Please explain.

Answer 1

There are three ordering services, as you might have already read in the doc - 

• 1. SOLO 
• 2. Kafka-based 
• 3. PBFT (pending)

The orderer interfaces are implemented in the orderer executable which is packaged as the fabric-orderer Docker image. So there are two configuration modes for the orderer - SOLO is a standalone process orderer for usage during development and testing. And Kafka-based service leverages Kafka as the "consensus" mechanism to make multiple orderer processes crash fault tolerant and order transactions. In this case, multiple orderer processes communicate with a Kafka cluster which ensures that each orderer process receives transactions and generates blocks in the same order. The orderer process (or fabric-orderer containers) communicate with a Kafka cluster.

Hope this helps :)