Hierarchical quorums in Zookeeper - apache-zookeeper

Question

I am trying to understand hierarchical quorums in Zookeeper. The documentation here
gives an example but I am still not quiet sure I understand it. My question is, if I have a two node Zookeeper cluster (I know it is not recommended but let's consider it for the sake of this example)
server.1 and
server.2,
can I have hierarchical quorums as follows:
group.1=1:2
weight.1=2
weight.2=2
With the above configuration:
Even if one node goes down I still have enough votes (?) to
maintain a quorum ? is this a correct statement ?
What is the zookeeper quorum value here (2 - for two nodes or 3 -
for 4 votes)
In a second example, say I have:
group.1=1:2
weight.1=2
weight.2=1
In this case if server.2 goes down,
Should I still have sufficient votes (2) to maintain a quorum ?

Answer 1

As far as I understand from the documentation, When we give weight to a node, then the majority varies from being the number of nodes. For example, if there are 10 nodes and 3 of the nodes have been given 70 percent of weightage, then it is enough to have those three nodes active in the network. Hence,
You don't have enough majority since both nodes have equal weight of 2. So, if one node goes down, we have only 50 percent of the network being active. Hence quorum is not achieved.
Since total weight is 4. we require 70 percent of 4 which would be 2.8 so closely 3, since we have only two nodes, both needs to be active to meet the quorum.
In the second example, it is clear from the weights given that 2/3 of the network would be enough (depends on the configuration set by us, I would assume 70 percent always,) if 65 percent is enough to say that network is alive, then the quorum is reached with one node which has weightage 2.