minimum number of journal nodes needed.

[#1]

I have a question. What is the minimum number of journal nodes that are required for a cluster which is in namenode HA mode? From what I understand what the role of journal node is, only one or two should also be enough (even though in your example you have 3 journal nodes and even when I created a manual namenode HA cluster of 3 nodes, each node had a journal node totally again to 3 journal nodes) or is it that each node must have a journal node for example if I have 10 node cluster where I want to have NN HA enabled, will I require 10 journal nodes to be installed (one on each node)?

[#2 · Accepted solution]

In production type cluster (with 10's-100+ nodes) with Namenode HA enabled, best practice is to have 2 Namenodes (1 active and 1 standby) and 3 Journal nodes.

[#3]

@Rahul Reddy. Thank you for the reply. So, these 3 journal nodes don't have to be installed on specific nodes with specific services installed or they can be installed on separate nodes altogether. Am I right? Also why do we need 3 zookeeper servers?